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Abstract
This study delves into the dynamic modulation of photodetection characteristics in Al/NaSrLa(BO3)2/n-Si devices, focusing on their structural, electrical, and photoresponse properties. The research highlights the synthesis and characterization of the compound, including its phase purity, vibrational modes, and thermal stability. The fabricated photodiode demonstrates robust rectifying behavior and minimal leakage current, confirming the efficacy of the orthoborate interlayer. Key diode parameters, such as saturation current, barrier height, and ideality factor, are systematically evaluated under various illumination conditions. The device exhibits a near-linear photocurrent scaling with incident power density, achieving peak responsivity and detectivity under low illumination. Time-resolved measurements validate the photodiode's switching dynamics, with no observable hysteresis or signal degradation. The study concludes by establishing the potential of rare-earth orthoborates as promising interlayer materials for silicon-based photodetectors, paving the way for future optimization efforts in interfacial passivation and defect engineering.
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Abstract
This study presents the fabrication and characterization of a silicon-based heterojunction photodiode featuring a rare-earth orthoborate interlayer, aimed at enhancing high-sensitivity photodetection. The orthoborate compound was synthesized by the solid-state reaction method and confirmed to have high phase purity and thermal stability up to 800 C. Structural and spectroscopic analyses (PXRD, FTIR, and SEM/EDS) verified a uniform microstructure and well-defined borate framework. The device showed clear rectifying behavior with very low dark current, indicating good junction quality and effective carrier separation. Illumination induced systematic changes in ideality factor, barrier height, and saturation current, consistent with photon-assisted transport. The photodiode achieved high photosensitivity and stable responsivity across different illumination levels, particularly under low-light conditions. Under 100 \(mW\,cm^{ - 1}\) illumination, the responsivity reached \(0.43{ }A/W\) and specific detectivity exceeded \(2.5{ } \times 10^{10} {\text{ Jones}}\). Time-resolved measurements demonstrated rapid and repeatable switching with no hysteresis, confirming operational stability. These results demonstrate that the \(Al/NaSrLa\left( {BO_{3} } \right)_{2} /n - Si\) heterojunction is a promising platform for sensitive and stable photodetection in optoelectronic applications.
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1 Introduction
The rapid expansion of optoelectronic technologies, particularly in the domains of high-speed communications, biomedical sensing, and environmental monitoring, has intensified the demand for photodetectors with superior sensitivity, stability, and spectral versatility. Silicon, owing to its abundance, mature fabrication infrastructure, and well-established electronic properties, remains the cornerstone of modern optoelectronics [1‐3]. Nevertheless, the restricted spectral range and susceptibility to interface defects inherent to silicon highlight the need for functional material integration to extend and strengthen its photodetection capabilities. To this end, hybrid heterostructures that couple silicon with novel wide-bandgap, nanocomposites, polymers or 2D materials have emerged as a promising strategy for achieving broadband, efficient, and low-noise photodetectors [4‐6].
Among functional oxides, rare-earth borates have recently gained attention for their combination of wide bandgap, structural stability, and tunable optical transitions arising from the flexible coordination of boron–oxygen polyhedra (such as planar triangular (\(BO_{3}^{3 - }\)) and tetrahedral (\(BO_{4}^{4 - }\)) groups) [7‐9]. Their ability to incorporate trivalent rare-earth ions provides a powerful means to engineer the electronic band structure and local field environment, both of which are critical for charge transport at semiconductor interfaces. While borates have long been explored in nonlinear optics and luminescent systems, their application as active interfacial layers in silicon photodiodes has received minimal attention [10‐13]. Rare-earth orthoborates constitute a complementary materials platform for interface engineering. These compounds combine large optical bandgaps, strong chemical and thermal robustness, and low parasitic optical loss, while permitting compositional control through lanthanide substitution [14‐18]. When incorporated at a silicon junction, they offer distinct interfacial advantages: (i) chemical passivation that mitigates surface-state recombination, (ii) field-effect passivation through fixed charge or interfacial dipoles, and (iii) favorable band offsets that promote carrier selectivity without compromising transparency across the visible to near-infrared spectrum [19‐21]. Despite extensive research on oxide-based interlayers in silicon photodiodes, the functional integration of rare-earth orthoborates—particularly mixed alkali–lanthanide systems—remains largely unexplored. Prior studies have predominantly focused on conventional oxides such as \(ZnO\), \(TiO_{2}\), or \(Al_{2} O_{3}\), which serve primarily as passive dielectric barriers or electron transport layers [22‐25]. In contrast, orthoborate frameworks with trivalent lanthanide substitution can actively modulate interfacial charge dynamics, providing an avenue for the design of photodiodes with improved rectification and photoresponse characteristics [26]. Within this context, the \(NaSrLa\left( {BO_{3} } \right)_{2}\) orthoborate system emerges as an innovative candidate for integration with silicon. The incorporation of La3⁺ ions enhances lattice stability and introduces defect-tolerant energy levels favorable for charge transfer [27‐29]. When employed as an interlayer in Si-based photodiodes, this compound can suppress interface recombination, improve rectification behavior, and enhance photocurrent generation. The present work addresses this knowledge gap by synthesizing and evaluating a novel \(NaSrLa\left( {BO_{3} } \right)_{2}\) orthoborate compound as a functional interfacial layer in photodiode architectures. Through comprehensive electrical and photoresponse measurements, the study systematically evaluates the rectifying behavior, dark current suppression, photocurrent generation, and interfacial charge transport dynamics. By employing analytical models such as Cheung’s method, key diode parameters—namely the ideality factor, barrier height, and series resistance—are quantitatively determined with high accuracy. The findings not only highlight the potential of \(NaSrLa\left( {BO_{3} } \right)_{2}\) as an interfacial layer for enhancing silicon-based photodetectors but also clarifies the underlying principles that govern its functional performance properties.
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2 Experimental section
2.1 The synthesis of \(NaSrLa\left( {BO_{3} } \right)_{2}\) mixed-metal cation borate structure
The synthesis of \(NaSrLa\left( {BO_{3} } \right)_{2}\) was carried out by a multi-stage thermal protocol designed to ensure phase purity and compositional homogeneity. High purity starting materials were selected and weighed in stoichiometric ratios according to the target reaction procedure. The synthesis procedure is summarized in Scheme 1. The precursors were first ground in a mortar to ensure homogenization. After pre-annealing in a tube furnace at 150 °C for 3 h, the intermediate product was subjected to re-grinding to disrupt the sintered regions and ensure homogeneity before high-temperature synthesis. The dehydrated intermediate product was calcined at 400 °C for 4 h, then ground in a mortar again, and then annealed at 700 °C for 14 h for the synthesis reaction. In the final stage, the material underwent a final calcination step at 800 °C for 4 h to ensure complete crystallization of the \(NaSrLa\left( {BO_{3} } \right)_{2}\) phase. A detailed account of the multistep solid-state synthesis protocol, encompassing intermediate thermal treatments, repeated milling stages, and crystallization dynamics, is available in our earlier study on rare-earth orthoborate materials, which describes an analogous synthesis pathway comprehensively [30].
Scheme 1
Reaction scheme for the solid-state synthesis of \(NaSrLa\left( {BO_{3} } \right)_{2}\) compound
This high-temperature treatment ensured the elimination of residual volatiles and unreacted precursors, while stabilizing the desired orthoborate structure. After calcination, the furnace was allowed to cool naturally to room temperature to prevent thermal shock and preserve lattice integrity. The resulting reaction products were then cooled to room temperature in a dehumidified desiccator and finally ground in a mortar to ensure homogenization. Formulation verification was achieved by analyzing the chemical composition of the resulting product using ICP-MS (Table 1), Fig. 1.
Table 1
Comparison of experimental and theoretical elemental composition percentages of \(NaSrLa\left( {BO_{3} } \right)_{2}\)
The compositional study of the \(NaSrLa\left( {BO_{3} } \right)_{2}\) borate structure reveals strong consistency between the experimentally obtained data and the calculated theoretical values, as summarized in Table 1. The experimentally obtained elemental contents of Na (6.45%), Sr (24.08%), La (38.51%), and B (6.22%) closely match the theoretical values of Na (6.26%), Sr (23.87%), La (37.84%), and B (5.89%), with only minor deviations in the range of \(0.2 - 0.7\%\). Such a high level of agreement confirms that the synthesized compound exhibits the intended stoichiometry with remarkable accuracy, indicating the reliability and reproducibility of the synthesis method. A closer examination of the individual elements reveals that Sr shows nearly perfect correspondence with its theoretical ratio, while Na and B exhibit slightly higher experimental values, which may be attributed to minor surface effects or instrumental sensitivity. The La content also shows a marginally higher experimental percentage, yet this deviation remains within acceptable analytical error.
2.2 Fabrication procedure of \(NaSrLa\left( {BO_{3} } \right)_{2}\) based devices
To prepare the silicon substrates for thin-film integration, a sequenced surface treatment was implemented to ensure chemical cleanliness and interfacial reliability. The process commenced with immersion in acetone under ultrasonic agitation for 10 min, effectively dislodging organic residues and surface-bound contaminants. Subsequently, the sample was rinsed with high-resistivity DI water and dried using a directed N2 flow to eliminate any residual solvent. The Si substrate was treated by immersion in buffered hydrofluoric acid for 2 min, a step designed to dissolve the native \(SiO_{2}\) layer and generate a reactive silicon surface. Rapid transfer to a deionized water bath and subsequent nitrogen drying minimized the risk of reoxidation, yielding a pristine substrate surface suitable for subsequent film deposition.
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Subsequently, a rear-side aluminum layer was thermally evaporated to form a stable ohmic contact, ensuring low-resistance electrical contact in subsequent device fabrication. Post-deposition annealing was performed at 450 °C for 3 min under nitrogen ambient to enhance interfacial alloying and reduce contact resistance. The \(NaSrLa\left( {BO_{3} } \right)_{2}\) layer was deposited onto the preconditioned Si substrates using a spin-coating technique optimized for uniformity and adhesion. Precursor solutions were dispensed onto the Si front surface and spun at 3000 rpm for 30 s, yielding a continuous and homogeneous \(NaSrLa\left( {BO_{3} } \right)_{2}\) thin film. Production steps for \(Al/NaSrLa\left( {BO_{3} } \right)_{2} /n - Si\) photodiode was illustrated Fig. 2a. Following deposition, the Si bearing the functional coating was thermally conditioned at 100 °C for 10 min. The post-coating annealing treatment was employed to facilitate the efficient removal of residual solvent and to strengthen the interfacial adhesion between the deposited film and the underlying Si substrate. The intermediate treatment was applied to maintain film integrity during subsequent thermal processing and for minimizing interfacial defects. Following film deposition, top Al contacts were fabricated via thermal evaporation under high vacuum conditions. The deposition rate was maintained at 0.5 Å/s, resulting in a metallic layer with an approximate thickness of 150 nm. Contacts were achieved via a high-precision shadow masking technique, facilitating consistent fabrication of circular contact profiles with excellent reproducibility across samples. Following fabrication, the \(Al/NaSrLa\left( {BO_{3} } \right)_{2} /n - Si/Al\) device structure (as presented in Fig. 2b) was analyzed through I–V and I–t measurements under a range of illumination conditions, using the Fytronix Solar Simulator to assess its optoelectronic response.
Fig. 2
a Production steps for \(Al/NaSrLa\left( {BO_{3} } \right)_{2} /n - Si\) photodiode and b Schematic device structure
3.1 Structural properties of \(NaSrLa\left( {BO_{3} } \right)_{2}\) compound
The \(NaSrLa\left( {BO_{3} } \right)_{2}\) compound was structurally characterized through powder X-ray diffraction (P-XRD), and the diffraction patterns recorded in the 2θ range of 5°–70° are displayed in Fig. 3. Comparison with the reference pattern (PDF card No. 01–080-2890) reveals a strong match, supporting the conclusion that the synthesized material shares structural features with reported mixed-metal borates [31, 32]. The observed correlation confirms the reliability of the proposed chemical formulation. A comparative summary of the diffraction peak positions between our synthesized structure and the reference data is presented in Table 2, further validating the crystallographic integrity of the \(NaSrLa\left( {BO_{3} } \right)_{2}\) framework.
Fig. 3
Powder XRD pattern of \(NaSrLa\left( {BO_{3} } \right)_{2}\) compound
To validate the structural integrity and confirm the successful formation of the \(NaSrLa\left( {BO_{3} } \right)_{2}\) compound, Fourier Transform Infrared (FTIR) spectroscopy was employed as a complementary characterization technique. FTIR analysis is particularly suitable for elucidating the vibrational modes of functional groups and thereby contributing meaningful knowledge regarding the structural configuration of borate systems. The obtained spectrum exhibited well-defined absorption bands that can be systematically correlated with the characteristic vibrations of the borate framework. Strong absorption peaks located in the 1446–1071 \(cm^{ - 1}\) region were assigned to the asymmetric stretching vibrations of trigonal \(BO_{3}^{3 - }\) units, which clearly indicate the presence of ordered borate groups within the lattice. Additional bands observed between 940–817 cm−1 correspond to B–O stretching vibrations, further substantiating the integrity of the borate units. The spectral features detected in the 785–606 cm−1 range were attributed to the bending vibrations of B–O–B linkages, reflecting the connectivity of the borate network. Moreover, distinct absorption bands in the lower-frequency region (600–400 cm−1) were associated with Sr–O, Na–O, and La–O stretching vibrations, providing compelling evidence for the coordination of alkali and rare-earth cations within the crystal lattice. Collectively, these results confirm the formation of a stable borate framework in \(NaSrLa\left( {BO_{3} } \right)_{2}\), and Table 3 contains the assignment of the observed vibrational bands Fig. 4.
Table 3
A summary of the FTIR peak values for \(NaSrLa\left( {BO_{3} } \right)_{2}\) compound
Compound
BO33− asymmetric vibration (\(cm^{ - 1}\))
BO33− B-O bond stretching vibration (\(cm^{ - 1}\))
Bending vibration of the B-O-B bond (\(cm^{ - 1}\))
Sr–O bond stretching vibration (\(cm^{ - 1}\))
Na–O bond stretching vibration (\(cm^{ - 1}\))
La–O bond stretching vibration (\(cm^{ - 1}\))
\(NaSrLa\left( {BO_{3} } \right)_{2}\)
1446–1071
940–817
785–606
606–592
565v547
522–404
Fig. 4
FTIR spectrum of the \(NaSrLa\left( {BO_{3} } \right)_{2}\) compound
These spectral assignments are further corroborated by comparative analysis with structurally analogous rare-earth borates reported in the literature. Notably, the asymmetric stretching vibrations of \(BO_{3}^{3 - }\) units observed in the 1446–1071 \(cm^{ - 1}\) region are in close agreement with those reported for \(Lu_{2} Ba_{3} B_{6} O_{15}\) and \(NaSrNd\left( {BO_{3} } \right)_{2}\), both of which exhibit similar trigonal borate coordination geometries and crystallographic environments [30, 33]. Likewise, the B–O stretching and B–O–B bending modes spanning 940–606 \(cm^{ - 1}\) are consistent with vibrational features reported for mixed-metal orthoborates and pyroborates, indicating the preservation of a robust and interconnected borate substructure [34]. Furthermore, the low-frequency bands vibrations align well with those observed in alkali-earth and lanthanide borate systems, reinforcing the successful incorporation of these cations into the lattice framework [35, 36]. These comparative observations not only validate the structural interpretation but also affirm the fidelity of the synthesis protocol and the crystallographic coherence of the resulting compound.
The structural and vibrational analyses of the \(NaSrLa\left( {BO_{3} } \right)_{2}\) compound were complemented by thermal characterization to evaluate its thermal stability and decomposition behavior. The thermal behavior of the synthesized \(NaSrLa\left( {BO_{3} } \right)_{2}\) structure was examined by simultaneous DTA analysis, and three distinct endothermic peaks were observed in the DTA curves, appearing in the temperature intervals of approximately 100–200, 400–600, and 600–800 °C. These thermal events were not accompanied by significant mass changes in the TG curves, with the overall weight loss being limited to ~ 1%, which can reasonably be attributed to residual acetate species not fully decomposed during the synthesis process. The negligible mass change across these regions indicates that the compound retains high structural stability under thermal stress. Furthermore, a noticeable weight loss of about 3% was detected near 850 °C, which is in good agreement with previous reports [27, 37]. This high-temperature mass reduction is generally associated with the evaporation of unreacted boron-containing species in the form of volatile oxides. On this basis, 800 °C was identified as the appropriate upper synthesis temperature limit, beyond which partial decomposition processes become significant. On this basis, 800 °C was identified as the appropriate upper synthesis temperature limit, beyond which partial decomposition processes become significant. Building upon the thermal characterization results, the thermal stability profile of \(NaSrLa\left( {BO_{3} } \right)_{2}\), as revealed by DTA measurements, is in strong agreement with literature-reported decomposition behavior of rare-earth borate systems. The negligible mass loss below 800 °C and the onset of decomposition near 850 °C are consistent with the volatilization thresholds of boron-containing species observed in Lu-based borates and \(NaSrR\left( {BO_{3} } \right)_{2}\), analogs [33, 35]. The observed stability up to 800 °C confirms the suitability of \(NaSrLa\left( {BO_{3} } \right)_{2}\) for high-temperature device integration and supports the reliability of the solid-state synthesis protocol. This comparative validation reinforces the conclusion that the synthesized compound maintains structural coherence under thermal stress Fig. 5
Fig. 5
Thermal analysis curves of the \(NaSrLa\left( {BO_{3} } \right)_{2}\) compound
3.2 Surface morphology and compositional characterization of \(NaSrLa\left( {BO_{3} } \right)_{2}\) compound
As illustrated in Fig. 6, the morphology and elemental composition of the \(NaSrLa\left( {BO_{3} } \right)_{2}\) compound were investigated by SEM and EDS analyses techniques. The SEM micrograph reveals a relatively homogeneous surface morphology with densely packed grains and well‑defined grain boundaries, indicative of controlled crystal growth and good structural integrity. EDS elemental mapping confirms the uniform spatial distribution of Na, Sr, La, B, and O across the examined area, with no evidence of phase segregation or compositional inhomogeneity. In the EDS analyses of mixed‑metal borates exhibiting a homogeneous, single‑phase surface structure, and detection of all metal cations specified in the molecular composition confirms the formation of the target phase. It should be noted, however, that SEM‑EDS provides instantaneous compositional data from localized regions of the surface; therefore, slight deviations from bulk composition values obtained by techniques such as ICP‑MS are expected. The SEM images and EDS results corroborate the homogeneous phase distribution of the constituent elements across the surface, supporting the conclusion that the \(NaSrLa\left( {BO_{3} } \right)_{2}\) compound was synthesized with high phase purity, uniform microstructural and compositional characteristics, consistent with the targeted crystal chemistry.
Fig. 6
SEM image and EDS analysis of \(NaSrLa\left( {BO_{3} } \right)_{2}\) compound
3.3 Photodiode performance and electrical characterization of \(NaSrLa\left( {BO_{3} } \right)_{2}\) compound
The performance of photodiode structures is fundamentally governed by their ability to convert incident photons into measurable electrical signals with high fidelity and stability. In this context, the \(Al/NaSrLa\left( {BO_{3} } \right)_{2} /n - Si\) heterojunction presents a compelling platform for optoelectronic applications, owing to its favorable material properties and compatibility with silicon-based device structures. The analysis of the current–voltage characteristics, it is essential to establish the operational framework under which the device was evaluated, including the influence of illumination intensity on carrier dynamics and junction behavior [38, 39]. The following discussion systematically examines the electrical response of the photodiode under various illumination conditions with emphasis on its rectification performance, photosensitivity, and suitability for light detection applications.
Figure 7-a. depicts the I–V characteristics of the \(Al/NaSrLa\left( {BO_{3} } \right)_{2} /n - Si\) photodiode on a linear scale within the voltage range of − 5 to + 5 V, measured under both dark and illuminated conditions. The device exhibits a clear rectifying behavior. In the absence of illumination (dark condition), the current remains very low in reverse bias, confirming efficient suppression of majority carrier transport and minimal leakage current. This low dark current is particularly advantageous for photodetection applications, as it directly contributes to a high signal-to-noise ratio and improved device sensitivity [40, 41]. Under forward bias, the current displays the expected exponential rise beyond the turn-on voltage, indicative of thermally activated carrier injection across the junction [42‐44]. The smooth increase in forward current further reflects efficient charge transport with negligible series resistance effects. This confirms that the \(Al/NaSrLa\left( {BO_{3} } \right)_{2} /n - Si\) interface behaves as a stable photodiode structure capable of reliable rectification. Upon illumination, a pronounced enhancement in current is observed throughout the entire voltage range. An increase in light intensity from 20 to 100 \(mW\,cm^{ - 1}\) leads to a gradual rise in both forward and reverse current values. Under reverse bias conditions, as the photocurrent grows in a nearly linear manner with increasing illumination power density. Such a linear dependence shows the predictable and stable photoresponse of the device, which is essential for quantitative light sensing and photodetection [45, 46]. The contrast between the dark and illuminated characteristics underscores the strong photosensitivity of the photodiode. Notably, no evidence of photocurrent saturation or anomalous response is detected within the studied intensity range, suggesting that the material system can operate effectively under varying illumination conditions without performance degradation. Figure 7-b. displays the semi-logarithmic current–voltage (I–V) characteristics of the \(Al/NaSrLa\left( {BO_{3} } \right)_{2} /n - Si\) photodiode at various illumination densities. The logarithmic scale provides a more detailed insight into the current behavior across several orders of magnitude, thereby enabling a clearer evaluation of leakage current, rectification ratio, and photoresponse efficiency [47, 48]. Under dark conditions, the device exhibits an relatively low reverse bias current, reaching the order of \(10^{ - 9} - 10^{ - 10} A\). Such minimal leakage current reflects the high quality of the junction interface and the suppression of defect-assisted conduction pathways [49, 50]. This characteristic is particularly advantageous for photodiodes, as it reduces noise and directly improves device detectivity. In forward bias, the current increases exponentially, consistent with thermionic emission or diffusion-dominated transport, further validating the diode-like response of the heterojunction [51].
Fig. 7
a Linear and b semi-logarithmic I–V characteristics of the \(Al/NaSrLa\left( {BO_{3} } \right)_{2} /n - Si\) photodiode measured under dark and varying illumination intensities
Upon illumination, a significant photocurrent enhancement is observed across the entire voltage spectrum. The reverse bias region shows the most pronounced increase, with current rising several orders of magnitude as the light intensity gradually increases. This trend confirms efficient generation and separation of photogenerated carriers within the depletion region of the heterojunction [52, 53]. The nearly parallel shift of the curves with increasing power density suggests that the photocurrent scales proportionally with illumination intensity, reflecting stable and predictable device operation. This implies that the \(Al/NaSrLa\left( {BO_{3} } \right)_{2} /n - Si\) photodiode not only maintains its diode integrity under illumination excitation but also demonstrates robust charge-selective transport. Furthermore, the absence of abnormal leakage currents or instability under high-intensity illumination confirms the reliability of the heterojunction for sustained optoelectronic applications.
The Thermionic Emission (TE) model, which explains the motion of charge carriers across a barrier, is widely applied to analyze the I–V characteristics of photodiode structures. This model is particularly applicable under moderate electric fields and elevated temperatures, where carrier motion is dominated by thermal excitation rather than tunneling or diffusion. Thermionic Emission theory offers a well-established analytical basis for modeling carrier transport across metal–semiconductor interfaces for analyzing the electrical behavior of heterojunction photodiodes and extracting key device parameters. According to TE theory, the forward bias current of a photodiode is expressed as [54, 55]:
In the above relations, “\(I\)” refers to the diode current (A), A is the active area of the photodiode (cm2), “R” is the Richardson constant (\(AK^{ - 2} cm^{ - 2}\)), “T” the absolute temperature (K), \(\phi_{B}\) the barrier height (eV), V the applied forward bias (V), “n” the ideality factor, “k” Boltzmann’s constant (\(1.38 \times 10^{ - 23} J/K\)), and “q” the elementary charge (\(1.6 \times 10^{ - 19} C\)). The saturation current (\(I_{0}\)), representing the current in the absence of applied voltage, is expressed in Eq. 2. Equation. 1 and Eq. 2form the basis for evaluating the ideality factor and barrier height from experimental I–V data, with the parameters calculated using the expressions given below [56‐58]:
In this study, the Richardson constant (R) is taken as 112 \(AK^{ - 2} cm^{ - 2}\), appropriate for n-type Si substrates [59]. The fabricated photodiode possesses an effective area of approximately 0.0015 \(cm^{2}\). Using this value together with the measured saturation current \(\left( {I_{0} } \right)\), the barrier height (\(\phi_{B}\)) can be accurately determined, while the “n” is obtained from the slope of the semi-logarithmic I–V plot.
As summarized in Table 4. and illustrated in Fig. 8., the electrical parameters of the \(Al/NaSrLa\left( {BO_{3} } \right)_{2} /n - Si\) photodiode were extracted under illumination intensities ranging from 0 to 100 \(mW\,cm^{ - 1}\). The analysis, based on the thermionic emission model (Eqs. 1–4), yielded values for “\(I_{0}\)”, “n”, and \(\phi_{B}\). These parameters shed light on the transport mechanisms, junction integrity, and overall photoresponse of the fabricated device. Under dark conditions, the junction exhibits a relatively low saturation current (\(1.03{ } \times 10^{ - 10} { }A\)) and a barrier height of 0.889 eV, signifying a well-defined potential barrier with limited defect-assisted leakage [60]. The corresponding ideality factor (n ≈ 3.86) slightly exceeds unity, implying minor deviation from ideal thermionic behavior due to localized inhomogeneities or interface-state participation [61, 62]. When the structure is exposed to 20 \(mW\,cm^{ - 2}\) illumination, “n” increases sharply to 4.86, which suggests that photogenerated carriers preferentially occupy shallow interface traps, thereby enhancing trap-assisted tunneling and recombination. Such behavior is characteristic of early photoactivation stages, where defect-mediated conduction pathways momentarily dominate the current flow [63, 64]. As the optical excitation intensifies, the ideality factor gradually decreases and approaches 3.95 at 100 \(mW\,cm^{ - 2}\). This progressive reduction reflects the saturation of recombination centers and a transition toward more homogeneous charge transport dominated by diffusion and thermionic emission. Concurrently, “\(I_{0}\)” rises consistent with enhanced photocarrier generation under stronger illumination. The effective barrier height exhibits a slight reduction—from 0.889 eV in the dark to 0.839 eV at elevated illumination—indicative of mild photo-induced band bending or transient interface dipole formation. Beyond ≈ 60 \(mW\,cm^{ - 2}\), \(\phi_{B}\) stabilizes near 0.84 eV, implying that a quasi-steady electronic equilibrium has been established at the interface [65, 66]. Taken together, these results reveal that the \(Al/NaSrLa\left( {BO_{3} } \right)_{2} /n - Si\)
Table 4
Electrical parameters of the fabricated \(NaSrLa\left( {BO_{3} } \right)_{2}\) -based photodiode
\(P(mW \cdot cm^{ - 2} )\)
\(n\)
\(I_{0} \left( A \right)\)
\(\phi_{{\varvec{B}}} \left( {eV} \right)\)
0
\(3.857\)
\(1.03 \times 10^{ - 10}\)
\(0.889\)
20
\(4.861\)
\(2.68 \times 10^{ - 9}\)
\(0.804\)
40
\(4.333\)
\(9.25 \times 10^{ - 10}\)
\(0.832\)
60
\(4.249\)
\(6.50 \times 10^{ - 10}\)
\(0.841\)
80
\(3.982\)
\(5.68 \times 10^{ - 10}\)
\(0.844\)
100
\(3.952\)
\(6.89 \times 10^{ - 10}\)
\(0.839\)
Fig. 8
Extracted values of n and \(\phi_{B}\) for the \(Al/NaSrLa\left( {BO_{3} } \right)_{2} /n - Si\) photodiode under illuminated environments
heterojunction maintains structural integrity and reproducible photoresponse over the entire intensity range. The device operates predominantly under the thermionic-emission regime, with secondary contributions from trap-assisted recombination at low photon flux [67]. Hence, the semi-logarithmic I–V representation not only confirms the rectifying nature of the junction but also serves as a diagnostic tool for quantifying the fundamental transport mechanisms governing device performance. Building on these observations, the analysis of dynamic resistance (\(R_{i}\)) as a function of various illuminated conditions provides complementary information into the device behavior. \(R_{i}\) captures the differential response of the junction and directly reflects the ease of carrier extraction at different operating points. The dependence of the \(R_{i}\) on illuminated conditions density is presented in Fig. 9 for bias voltages ranging from \(0.2{ }V\) to \(1{ }V\). Dynamic resistance, defined as the differential resistance at a given operating point, provides crucial information about the junction quality, carrier transport dynamics, and the sensitivity of the photodiode under illumination. At low illumination levels, \(R_{i}\) exhibits significantly high values, particularly at low bias voltages (e.g., \(\sim 65{ }k\Omega { }at{ }0.2{ }V\)). This behavior reflects the dominance of junction resistance in the absence of a strong photocurrent. As shown in Fig. 10, the dynamic resistance (\(R_{i}\)) increases with illumination intensity from 20 to 40 \(mW\,cm^{ - 2}\) and then decreases at higher intensities. The observed increase of dynamic resistance from \(mW\,cm^{ - 2}\) to 40 \(mV\,cm^{ - 2}\) can be attributed to illumination-induced modifications at the metal–semiconductor interface [68, 69]. At low intensities, photogenerated carriers occupy shallow interface traps, slightly lowering the potential barrier and reducing \(R_{i}\). As the illumination increases, these traps become saturated and the built-in potential partially recovers, resulting in a higher differential resistance. Beyond this range, further illumination increases the carrier density in the neutral region, which enhances current flow and decreases \(R_{i}\) again. This behavior confirms that the transport mechanism transitions from a trap-assisted process to a barrier-limited conduction regime with increasing optical excitation [70, 71]. As the various illuminated conditions increases, \(R_{i}\) decreases systematically, indicating efficient carrier generation and separation within the depletion region. The sharp decline in resistance between dark and illuminated states shows the pronounced impact of light excitation on charge transport properties. Another important observation is the bias-dependent nature of \(R_{i}\). At higher applied voltages \(( \ge 0.8{ }V\)), the resistance drops to very low values (approaching \(\sim \,10^{2\,} \Omega \,at\,100\,mW\,cm^{ - 2}\)). This behavior indicates that the applied bias significantly enhances carrier extraction efficiency, suppresses recombination pathways, and lowers the effective resistance across the junction interface. The relatively stable resistance values at high illumination intensities and bias voltages also confirm the robustness of the device against saturation effects, ensuring consistent photocurrent response across a wide dynamic range [58]. Additionally, the non-linear dependence of \(R_{i}\) on various illuminated conditions at intermediate biases (\(0.4 - 0.6{ }V\)) reveals subtle variations that may be associated with trap-assisted recombination or space-charge-limited conduction mechanisms. These features point toward complex carrier dynamics within the heterostructure, which may be further optimized by interface engineering or doping control. The strong decrease of \(R_{i}\) with light intensity confirms the suitability of this device for photodetection applications, where high sensitivity and low noise operation are essential.
Fig. 9
Dependence of dynamic resistance (\(R_{i}\)) on illumination level and applied bias in the \(Al/NaSrLa\left( {BO_{3} } \right)_{2} /n - Si\) photodiode
Analysis of the Cheung’s functions \(dV/dlnI\) and \(H\left( I \right)\) under dark conditions for the \(Al/NaSrLa\left( {BO_{3} } \right)_{2} /n - Si\) photodiode
The decrease of dynamic resistance with illumination intensity discussed above can be further quantified through analytical formalisms that account for series resistance and barrier modification effects. In particular, Cheung’s method introduces two characteristic functions [72‐74];
$$\frac{dV}{{dlnI}} = n\frac{kT}{q} + IR_{s}$$
(5)
$$H\left( I \right) = V - n\frac{kT}{q}ln\left( {\frac{I}{{ART^{2} }}} \right) = n\phi_{B} + IR_{s}$$
(6)
The linearity of the \(dV/dlnI - I\) and \(H\left( I \right) - I\) plots in the forward bias region enables the extraction of \(R_{s}\) and provides a more rigorous basis for interpreting the resistive effects observed in Fig. 11. and Fig. 12. The electrical transport parameters of the \(Al/NaSrLa\left( {BO_{3} } \right)_{2} /n - Si\) photodiode, were further analyzed using Cheung’s method in order to account for the influence of series resistance and interfacial barrier modification. Figure 10 illustrates the variation of the two characteristic curves, \(dV/dlnI - I\) and \(H\left( I \right) - I\), with current under dark conditions. The \(dV/dlnI\) plot exhibits a nearly linear dependence on current in the forward bias regime, which is consistent with Eq. (5) and confirms the suitability of the formalism for extracting the series resistance (\(R_{s}\)) of the device. Extrapolation of the linear segment grants straightforward access to \(R_{s}\), ensuring greater accuracy compared with traditional I–V characterization. Similarly, the \(H\left( I \right)\) function demonstrates a well-defined linear response over the same current range, as expected from Eq. (6). The slope of this curve is also related to \(R_{s}\), while the intercept yields the product of the “\(n\)” and “\(\phi_{B}\)”. The consistency between the \(dV/dlnI\) and \(H\left( I \right)\) analyses highlights the reliability of this approach and confirms that the transport in the forward bias region is strongly influenced by resistive effects in series with the diode junction. Overall, the extracted values not only quantify the internal resistance but also provide insight into the quality of the metal–semiconductor contact and the degree of deviation from ideal thermionic emission. As shown in Fig. 11, the behavior of Cheung’s functions (\(dV/dlnI\) and \(H\left( I \right)\)) was analyzed as a function of current under 100 \(mW\,cm^{ - 2}\) illumination for the \(Al/NaSrLa\left( {BO_{3} } \right)_{2} /n - Si\) photodiode. The \(dV/dlnI\) function shows a gradual increase with current, indicating a non-constant ideality factor across the measured range. This variation suggests that recombination mechanisms and carrier transport are not strictly ideal and may involve contributions from interface states or trap-assisted processes, particularly under high injection conditions [75]. The \(H\left( I \right)\) function, which incorporates both the voltage drop and the influence of series resistance, exhibits higher values than \(dV/dlnI\) throughout the current range. This elevation reflects the additional voltage contribution from resistive elements within the device, such as contact resistance or bulk resistance in the \(Al/NaSrLa\left( {BO_{3} } \right)_{2} /n - Si\) layer. The increase in \(H\left( I \right)\) with current confirms that the series resistance remains relatively constant and does not dominate the device behavior at moderate injection levels. In photodiode architectures, the \(R_{s}\) acts as a parasitic element that introduces voltage drops across the contacts and bulk layers, thereby reducing the effective bias across the depletion region [76]. This attenuation weakens the internal electric field required for efficient carrier separation and becomes particularly limiting under low illumination, where the photogenerated carrier density is insufficient to overcome resistive losses. As a result, the photocurrent is suppressed and the responsivity declines, constraining the dynamic range and signal-to-noise ratio of the device. Although the linearity observed in the \(dV/dlnI - I\) and \(H\left( I \right) - I\) plots confirms that \(R_{s}\) remains relatively stable across the measured current range, its presence still distorts the internal field distribution and can lead to recombination-enhanced transport, especially under forward bias. These resistive effects, while not dominant, cumulatively degrade the photodiode’s performance ceiling and may obscure accurate extraction of intrinsic parameters such as barrier height and ideality factor. Moreover, the absence of inflection points or nonlinearities in the \(H\left( I \right)\) profile suggests that the barrier height remains spatially uniform and that the junction does not suffer from significant inhomogeneity under illumination. The consistency of both \(dV/dlnI\) and \(H\left( I \right)\) functions supports the reliability of the extracted parameters and reinforces the conclusion that the device operates within the thermionic emission regime with minimal influence from parasitic effects. This approach complements the conventional I–V analysis and provides validation of the photodiode’s suitability for high-sensitivity optoelectronic applications.
Fig. 11
Cheung’s function analysis (\(dV/dlnI\) and \(H\left( I \right)\)) of the \(Al/NaSrLa\left( {BO_{3} } \right)_{2} /n - Si\) photodiode, measured as a function of current under 100 mW·cm⁻2 illumination
The relationship between photocurrent generation and incident light intensity in photodiodes is commonly described by a power-law expression of the form [77, 78]:
$$I_{ph} \propto P^{\theta }$$
(7)
where \(I_{ph}\) denotes the photocurrent and \(P\) represents the incident illumination power density. The exponent \(\theta\) serves as a critical figure of merit, quantifying the device’s sensitivity to variations in illumination. A value of \(\theta = 1\) corresponds to an ideal linear response, indicating that the photocurrent scales proportionally with light intensity. Deviations from unity suggest the presence of non-idealities such as trap-assisted recombination, carrier saturation, or space-charge effects, particularly at elevated illumination levels. In the case of the \(Al/NaSrLa(BO_{3} )_{2} /n - Si\) photodiode, the experimental data reveal a near-linear dependence of photocurrent on incident power density under reverse bias conditions. This behavior is highly desirable for photodetection applications, as it ensures a predictable and stable photoresponse across a broad dynamic range. The lack of saturation or irregularities across the examined illumination range reinforces the structural integrity of the junction and affirms the effectiveness of the carrier extraction process [79].
From the photocurrent–power density plot (as shown in Fig. 12), the calculated power‑law exponent \(\theta = \,0.9001\) confirms that the photocurrent scales nearly linearly with illumination intensity. Log–log fitting yielded a high correlation coefficient, R2 = 0.994 indicating excellent agreement between the experimental data and the power-law model. This value, closely approaching unity, confirms that the \(Al/NaSrLa\left( {BO_{3} } \right)_{2} /n - Si\) heterojunction exhibits quasi-ideal photoconductive behavior under reverse bias. Such linearity is indicative of efficient photocarrier generation, minimal trap-assisted recombination, and effective charge separation across the interface [80, 81]. Additionally, the observed shift in the forward turn-on voltage under illumination suggests barrier lowering, likely due to the accumulation of photogenerated carriers at the interface. This effect facilitates charge injection and further amplifies the forward current response. Thereby preserving the linearity of the photoresponse. The resulting increase in forward current under illumination supports the presence of strong internal photoelectric field effects and efficient carrier transport dynamics. These attributes collectively validate the \(Al/NaSrLa\left( {BO_{3} } \right)_{2} /n - Si\) heterojunction as a promising candidate for high-performance photodetector applications requiring quantitative light sensing and reproducible response under variable illumination conditions.
To further elucidate the optoelectronic performance of the \(Al/NaSrLa\left( {BO_{3} } \right)_{2} /n - Si\) photodiode, a quantitative assessment of its photosensitivity (K) and responsivity (R) under varying illumination intensities was conducted. These parameters offer information about the device’s ability to convert incident power illumination intensity into measurable electrical signals and are essential for benchmarking photodetector efficiency. To support this analysis, the fundamental expressions governing photodiode performance metrics are outlined below. These equations form the basis for calculating the photocurrent, photosensitivity, responsivity, and specific detectivity, each of which contributes to a comprehensive understanding of the device’s operational characteristics [82‐84]:
In these expressions, the net photocurrent is expressed as \(I_{ph}\), with \(I_{illuminate}\) and \(I_{dark}\) indicating the recorded current values in light and dark conditions, respectively. In this context, “P” denotes the incident power density, “A” the active area of the photodiode, and “q” the elementary charge. These parameters collectively enable a rigorous evaluation of the photodiode’s sensitivity and detection capabilities, which are further explored in the context of spectral detectivity in the following section.
The graphical representation in Fig. 13 provides a comparative analysis of photosensitivity (K) and responsivity (R) as functions of incident power density for the \(Al/NaSrLa\left( {BO_{3} } \right)_{2} /n - Si\) photodiode. The photosensitivity curve demonstrates a clear increase across the measured intensity range, rising from 13.99 at 20 \(mW\,cm^{ - 2}\) to 59.51 at 100 \(mW\,cm^{ - 2}\). This behavior indicates a progressively stronger photocurrent response relative to the dark current, suggesting that the device maintains efficient carrier generation and extraction even under elevated illumination conditions [85]. The linearity of this increase further implies minimal saturation effects within the tested range, affirming the photodiode's suitability for technologies that rely on high differential sensitivity. Conversely, the responsivity curve shows a steady reduction as the power density increases, falling from \(0.51 A/W\) at 20 \(mW\,cm^{ - 2}\) to 0.43 \(A/W\) at 100 \(mW\,cm^{ - 2}\). This inverse trend reflects the diminishing marginal gain in photocurrent per unit incident power, which is characteristic of photodiodes approaching their dynamic range limits. The reduction in responsivity may be attributed to recombination losses, space-charge effects, or trap-mediated carrier dynamics that become more pronounced at higher carrier injection levels [86]. Notably, the responsivity remains above 0.40 \(A/W\) throughout the range, indicating that the device retains a substantial conversion efficiency despite the onset of saturation. The in Fig. 14, the lower-intensity region corresponds to the point of maximum responsivity and detectivity, where the signal-to-noise ratio is most favorable. This regime is particularly relevant for low-light detection scenarios. The higher-intensity region marks the onset of responsivity degradation, suggesting that further increases in illumination yield diminishing returns in electrical output. As summarized in Fig. 14 and Table 5, the device exhibits its maximum responsivity of 0.51 \(A/W\) and peak detectivity (\(D^{*}\)) of \(3.32 \times 10^{10} {\text{ Jones}}\) at an illumination intensity of 20 \(mW\,cm^{ - 2}\), demonstrating its superior photo-to-electrical conversion efficiency under low-light conditions. As the illumination level increases, both responsivity and detectivity show a gradual decline, reaching 0.43 \(A/W\) and \(2.83 \times 10^{10} {\text{ Jones}}\) at 100 \(mW\,cm^{ - 2}\). This decrease is mainly attributed to enhanced carrier recombination, trap filling, and space-charge accumulation, which reduce the effective collection of photogenerated carriers and slightly elevate the junction temperature, thereby lowering the conversion efficiency. Despite this reduction, the responsivity remains above 0.40 \(A/W\) across the entire range, confirming stable charge transport and high carrier extraction efficiency even at high photon flux.
Fig. 13
K–P and R–P plots of \(Al/NaSrLa\left( {BO_{3} } \right)_{2} /n - Si\) photodiode under illumination intensity
Complementary to the graphical trends in listed Table 5. confirming its high sensitivity under low illumination. As the power density increases to 40 and 60 \(mW\,cm^{ - 2}\), the photocurrent nearly doubles at each step, while responsivity remains stable and detectivity shows only marginal decline in Fig. 15. This stability suggests that the device operates within its optimal dynamic range up to approximately 60 \(mW\,cm^{2}\). Beyond this threshold, at 80 and 100 \(mW\,cm^{ - 2}\), the responsivity begins to decline more noticeably. These reductions are indicative of performance saturation, likely driven by increased recombination and thermal noise contributions. Nevertheless, the photosensitivity continues to rise, reaching 59.51 at 100 \(mW\,cm^{ - 2}\), which underscores the device’s capacity to maintain a strong differential response even as absolute efficiency diminishes. The \(Al/NaSrLa\left( {BO_{3} } \right)_{2} /n - Si\) photodiode device demonstrates high photosensitivity, stable responsivity, and competitive detectivity, particularly under low to moderate illumination conditions. The combination of these traits positions the device as an attractive platform for photodetection technologies requiring both sensitivity and dynamic range stability.
Fig. 15
a I-t measurement and b rise/fall time plots of the \(Al/NaSrLa\left( {BO_{3} } \right)_{2} /n - Si\) photodiode
To complement the steady-state electrical characterization of the \(Al/NaSrLa\left( {BO_{3} } \right)_{2} /n - Si\) photodiode, a time-resolved photocurrent analysis was conducted to evaluate the device’s dynamic response under periodic illumination. This measurement provides information about the temporal stability, reproducibility, and switching behavior of the photodiode, which are key parameters for real-time sensing and optoelectronic modulation applications [87, 88]. Figure 15-a presents the I–t profile of the device recorded over an extended duration under controlled illumination cycles. The I–t graph reveals a series of well-defined photocurrent peaks and troughs, corresponding to successive light-on and light-off intervals. The periodic nature of the response confirms that the device exhibits consistent and repeatable behavior across multiple illumination cycles. The sharp rise in photocurrent upon illumination and its rapid decay upon cessation of light exposure indicate fast carrier generation and recombination dynamics, suggesting minimal trapping or delay effects at the interface. This behavior is characteristic of photodiodes with low defect density and efficient carrier extraction pathways [89]. The amplitude of the photocurrent remains stable throughout the measurement window. This high on/off current ratio validates the device’s photosensitivity and its ability to distinguish between illuminated and non-illuminated states with high fidelity. The absence of drift, hysteresis, or degradation in signal amplitude over time shows the photodiode’s operational stability and its potential for long-term deployment in light-sensing environments. By combining a strong static photoresponse with dependable dynamic characteristics, the \(Al/NaSrLa\left( {BO_{3} } \right)_{2} /n - Si\) photodiode proves to be well-suited for applications that demand rapid and reproducible light detection, such as optical communication, imaging arrays, and environmental monitoring systems. The rise time of a detector is defined as the duration required for the current to increase from 10 to 90% of its maximum value, while the fall time corresponds to the time needed for the current to drop from 90 to 10% of its maximum value. Figure 15-b presents the rise and fall times measured at an intensity of 100 mW/cm2. The rise times were determined to be 389, 707, 773, 699, and 607 ms at incident intensities of 20, 40, 60, 80, and 100 mW/cm2, respectively. The corresponding fall times were calculated as 180, 436, 488, 540, and 882 ms for the same intensity levels. Overall, these response times are relatively slow compared with those of high-speed photodetectors.
To contextualize the performance of the \(Al/NaSrLa\left( {BO_{3} } \right)_{2} /n - Si\) photodiode within the broader family of rare-earth orthoborate interlayers, a comparative analysis was conducted using key figures of merit: “K”, “R”, and “D*”. Table 6 summarizes the reported values for various orthoborate-based heterojunctions interfaced with silicon substrates, enabling a direct evaluation of how compositional variations influence photodetector behavior. The data reveal that devices incorporating \(KCaSm\left( {BO_{3} } \right)_{2}\) exhibit the highest photosensitivity (\(K = 194.28\)), although this is accompanied by a relatively low responsivity of \(0.16 A/W\). This suggests that while the differential current response is strong, the absolute photocurrent per unit incident power is limited, potentially due to inefficient carrier extraction or recombination losses. In contrast, \(NaSrEr\left( {BO_{3} } \right)_{2} { }\) demonstrates the highest responsivity (\(2.38 A/W\)) and detectivity (\(7.82{ } \times 10^{10} {\text{ Jones}}\)), indicating superior photon-to-current conversion efficiency and noise suppression. The p-type configuration may contribute to enhanced carrier mobility or reduced interface recombination, accounting for the elevated performance. Devices based on \(KSrSm\left( {BO_{3} } \right)_{2}\) and \(NaSrLa\left( {BO_{3} } \right)_{2}\) show comparable photosensitivity values (\(60.34\) and \(59.51\), respectively), yet differ in responsivity and detectivity. The \(Al/NaSrLa\left( {BO_{3} } \right)_{2} /n - Si\) photodiode developed in this work achieves a balanced profile, with \(R = 0.43 A/W\) and \(D^{*} = 2.83 \times 10^{10} {\text{ Jones}}\), placing it among the more efficient n-type configurations. Its performance surpasses that of \(KCaLa\left( {BO_{3} } \right)_{2} /Si\) and \(KCaNd\left( {BO_{3} } \right)_{2} /Si\), both of which exhibit lower detectivity despite moderate responsivity values. The comparative trends show the importance of both cation selection and substrate type in tailoring photodetector performance. While high photosensitivity may indicate strong light–matter interaction, it must be complemented by efficient carrier transport to achieve high responsivity and detectivity. The \(Al/NaSrLa\left( {BO_{3} } \right)_{2} /n - Si\) device demonstrates competitive metrics across all categories, validating its potential for integration into silicon-based optoelectronic platforms.
Table 6
Comparative performance metrics of \(Al/NaSrLa\left( {BO_{3} } \right)_{2} /n - Si\) heterojunction and other orthoborate-based photodiodes reported in the literature
This work presents a comprehensive optoelectronic evaluation of a \(Al/NaSrLa\left( {BO_{3} } \right)_{2} /n - Si\) heterojunction photodiode, wherein the rare-earth orthoborate interlayer was employed to modulate interface properties and enhance device performance. The synthesized \(NaSrLa\left( {BO_{3} } \right)_{2}\) compound exhibited phase purity, distinct borate vibrational modes, and thermal stability up to ~ 800 °C, thereby confirming its reliability as a stable interfacial material for silicon-based architectures. SEM/EDX analyses showed homogeneous elemental distribution, supporting its suitability for uniform film formation on Si substrates. Through systematic electrical characterization, the fabricated structure demonstrated robust rectifying behavior and minimal leakage current, confirming the efficacy of \(NaSrLa\left( {BO_{3} } \right)_{2}\) as a functional interfacial material for silicon-based photodetectors. The optoelectronic performance of the \(Al/NaSrLa\left( {BO_{3} } \right)_{2} /n - Si\) heterojunction photodiode was quantitatively benchmarked across multiple illumination regimes, revealing a robust and tunable photoresponse. Key diode parameters—including a dark saturation current of \(1.03 \times 10^{ - 10} {\text{ A}}\), barrier height of 0.889 eV, and ideality factor modulation under illumination—confirmed efficient interfacial transport governed by photon-assisted energetics. The device exhibited a near-linear photocurrent scaling with incident power density, characterized by a power-law exponent of 0.90, indicative of quasi-ideal photoconductive behavior. Peak responsivity of 0.51 \(A/W\) and maximum detectivity of \(3.32{ } \times 10^{10} {\text{Jones}}\) were recorded under low illumination, with stable performance maintained up to 100 \(mW\,cm^{ - 2}\), demonstrating resilience against saturation effects. Time-resolved I–t measurements further validated the photodiode’s switching dynamics, with rise times ranging from 0.389 s to 0.773 s and decay times ranging from 0.180 s to 0.882 s, with no observable hysteresis or signal degradation. These results establish \(NaSrLa\left( {BO_{3} } \right)_{2}\) as a promising interlayer material for silicon-based photodetectors, combining high sensitivity, dynamic range stability, and temporal fidelity. Future optimization efforts may focus on interfacial passivation, spectral selectivity tuning, and defect engineering, which could further enhance carrier extraction, noise suppression, and wavelength-specific response. The methodological framework presented here offers a scalable pathway for integrating rare-earth orthoborates into advanced optoelectronic platforms.
Declarations
Conflict of interest
The authors declare no competing interests.
Declaration of generative AI in scientific writing
The writing process incorporated generative AI and AI-supported technologies, which were applied only to refine language and improve readability.
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