HEMT Technology and Applications

This chapter reviews the recent progress in ultrawide bandgap AlGaN-channel-based high electron mobility transistors. AlGaN channel is the alternate substitute for the conventional GaN channel. In order to enhance the power handling capability of III-nitride-based heterostructure devices, improving the breakdown performance of the device without reduction in the current density is one of the simplest techniques. AlGaN-channel-based HEMTs favorably increase the critical electric field of the device. For the next-generation RF application, further improving the power handling capabilities of RF modules, AlGaN channel HEMT is the most optimistic applicant and it delivers four times larger GaN HEMT’s power performance and thus becoming the possible substitute to the GaN channel for the next generation power as well as RF devices and circuits. This chapter describes the polarization details of Al_xGa_1−xN/Al_yGa_1−yN heterostructure, and various device structure of AlGaN channel HEMTs and their static and dynamic characteristics.

Breakdown mechanisms play a significant role in determining the performance of AlGaN/GaN HEMTs in high-power circuit applications. This chapter presents a brief overview of various factors, which cause an early breakdown in AlGaN/GaN HEMT at high drain voltage. The chapter also covers technological advancements proposed so far by various research groups to enhance the breakdown voltage of the device. Further, scaling technologies are discussed to improve the high-frequency performance of the device.

The dielectric oxide Al₂O₃ induced gate recessed PZT ferroelectric Al_0.3Ga_0.7N/AlN/GaN MOSHEMT device behavior with different oxide thicknesses is analyzed in this work. The stack of different layers Al₂O₃/Al_0.3Ga_0.7N/AlN/GaN is grown on a silicon (Si) substrate. Gate recessed technique is used for achieving the normally off operation in the MOSHEMT. Normally off devices provide better control in gate leakage current and stability of threshold voltage (V_th). The ferroelectric material of lead zirconate titanate Pb(Zr,Ti)O₃ (PZT) is induced between the gate and oxide layer to obtain the enhancement type (E-Mode) operation to improve the device performance due to the strong polarization effect. The AlN spacer layer is introduced between the Al_0.3Ga_0.7N barrier and GaN Channel to increase mobility and 2-DEG confinement. For controlling the GaN channel layer, the AlN nucleation layer is inserted between GaN/Si–substrate interfaces by producing better surface morphology. Furthermore, silicon-based substrates are used to achieve excellent thermal characteristics. Due to the polarization effect, a two-dimensional electron gas (2-DEG) is created at the Al_0.3Ga_0.7N/GaN interface. The analog performance parameters like drain current (I_d), output characteristics (I_d − V_d), transconductance (gm), cutoff frequency (f_T), and gate-to-source capacitance (C_gs) except maximum frequency of oscillation (F_max) show an improvement for 3 nm oxide layer thickness of Al₂O₃. The results of the proposed device Al_0.3Ga_0.7N/AlN/GaN PZT GR-MOSHEMT shows an impact on high power and RF-based devices. All the simulations are done by the commercial Silvaco Atlas Technology Computer-Aided Design (TCAD) tool.

ZnO material exhibits superior properties required for several electronic applications. It has been noticed that the different temperature-based models of conventional AlGaN/GaN HEMTs have been widely studied; however, physics-based analytical models including the effect of temperature for MgZnO/ZnO HEMT are not sufficiently explored much as of now in the literature. Accordingly, in this brief, the different transport properties and Fermi energy levels of AlGaN/GaN and MgZnO/ZnO HEMT are studied with respect to different temperatures. Further, we have also comparatively reviewed the important transport properties including 2DEG density, internal electric field, and optical gain of AlGaN/GaN and MgZnO/ZnO quantum well structures having identical dimensions.

An analytical modeling of electric field and breakdown voltage characteristics of AlInN/GaN HEMT with field plate at drain and gate regions is presented. In the model development, GaN buffer and Si substrate regions are treated as depletion regions. The developed model gives a deep physical understanding of the electric field and breakdown voltage characteristics of AlInN/GaN HEMT devices. The avalanche breakdown of a device appears in the vertical interface or edges of lateral field-plate structures. The relationship between vertical and lateral breakdown with respect to analytical modeling is presented. The breakdown characteristics are analyzed with device parameters including the thickness of regions, the length of field plate, and the distance between gate and drain. These analytical model characteristics are verified by matching with numerical simulations and are found in good agreement. The developed model can be used as an effective direction for the optimization of the device to accomplish better performance.

β-Ga₂O₃ HEMT with 10 nm AlN as a barrier layer is designed in this paper. The dielectric layer of Si₃N₄ and HfO₂ is introduced beneath the gate as a passivation layer. HfO₂ shows high thermal stability and high reliability while Si₃N₄ shows good interface attribute. The double gate of 0.2 µm and 0.5 µm with a gap of 50 nm aids in enhancing the 2DEG. The relation between dielectric constant and bandgap shows the interdependence on diametric size of the material. The passivation layer controls the gate leakage current and improves the pinch-off characteristics of the device. The transfer characteristic, transconductance, and output conductance demonstrate the device tunability for application in power radio frequency and microwave.

In this work, we present the effect of buried gate dimensions on electron mobility in a laterally gated AlN/β-Ga₂O₃ high-electron-mobility-transistor (HEMT) using 3D numerical simulations. The recessed parts of the gate laterally control the two-dimensional-electron-gas (2DEG) density in the channel as opposed to vertical control in the conventional planar HEMT. The constant low-field mobility model accounting for lattice temperature and field-dependent mobility model accounting for negative differential carrier mobility are evoked to analyze the electric field and carrier concentration by varying the channel width (W_C). A maximum drain current density of 0.8 and ~1 A/mm is obtained using a constant low-field and field-dependent mobility model, respectively, in the device with a gate length (L_G) of 0.1 µm and channel width of 100 nm. It is found that with increasing bias voltage, electron mobility starts decreasing due to rising lattice temperature in the constant low-field mobility model, whereas higher electric field-led carrier velocity saturation is attributed to lower mobility in the field-dependent mobility model.

Nowadays, the development of wide bandgap-based devices in power electronics has become more prominent to ameliorate the energy capability of devices. Furthermore, it can help reduce the total energy wastage in the world. Presently, AlGaN/GaN high-electron-mobility transistors (HEMTs) have shown excellent performance on the back of their extraordinary attributes like higher carrier density, and higher channel mobility over traditional wide bandgap devices like AlGaAs/GaAs. Because of the outstanding characteristics of the GaN HEMTs and their composited materials, they are becoming promising devices for the upcoming generation of more power and highest frequency-based implements. This chapter will provide a complete overview of the “Operation Principle of AlGaN/GaN HEMT.”

Gallium nitride (GaN) based High-Electron-Mobility Transistors (HEMTs), and in particular, aluminum gallium nitride (AlGaN)/GaN devices have become a popular choice due to their ability to produce higher power densities at higher frequencies as compared to their silicon (Si) and gallium arsenide (GaAs) based counterparts. GaN-based HEMTs have also proven to be excellent candidates for amplifiers operating at higher power levels, high temperatures, and in robust environments. This chapter discusses how the performance of such GaN-based HEMTs can be enhanced by introducing a gate oxide and an underlapped structure. The chapter also delves into the advantages of multigate structures and the use of quaternary indium aluminum gallium nitride (InAlGaN) compound to deliver higher breakdown voltage.

In recent days, wide bandgap semiconductor materials constructed with GaN are exhibiting incredible performances in developing devices that are handling applications like high power, high frequency, high reliability in switching speeds, etc. This device became most promising due to its matchless properties over the conventional technologies which use Si-based materials, specifically with their impressive electrical management features demonstrating in HEMT (High Electron Mobility Transistor) based on GaN material. This review reports the detailed study on performance analysis of GaN-based HEMTs, preferably in RF and Microwave Nanoelectronics applications, along with various aspects of the issues related to the device function.

High Electron Mobility Transistor (HEMT) attained great interest because of its superior electron transport making it suitable for applications in high-speed circuits and high power requirements. These devices are finding special interest to replace conventional field-effect transistors having outstanding performance in the domain of high-frequency applications. In HEMT, the high mobility of electrons and highly confined characteristics of the two-dimensional electron gas made sure that modulation doping could be utilized to have high-speed field-effect transistors having brilliant “Short Channel Effects” (SCEs) and excessive scope of scaling. However, lack of existing experimental results of such a device, designers require a dependable tool for simulation and analysis of the device characteristics in less time and low cost before device is fabricated for commercial use. Therefore, physics-based device simulator for design and performance prediction of the semiconductor device are very important. This book chapter describes an overview of the HEMT device and its physics-based simulation for performance analysis.

Gallium Nitride HEMT technology has been in focus for several decades due to its exemplary intrinsic properties. It provides a viable solution for the RF and high power Applications. The strong bonding nature of such III–V binary and ternary compounds ensures robustness to ionizing radiations for Space Electronics. In this regard, GaN has established itself as the dominating material for fulfilling the needs of future RF and high power applications. This article brings a brief overview of the current technology trends in HEMTs for next-generation Space Electronics with a deliberate focus toward TCAD-based studies.

On the back of the large energy bandgap, ultrawide bandgap (UWBG) materials have shown superior figures of merit for device performance in high-power and high-frequency applications. Among emerging UWBG semiconductors of interest, gallium oxide (Ga₂O₃) has a distinctive advantage over its peers mainly due to the availability of high-quality bulk crystals grown using cost-effective melt-based techniques. Furthermore, bandgap energy of ~5 eV makes Ga₂O₃ highly suitable for high-voltage devices. Related to high-speed device technologies, high-electron-mobility-transistors (HEMTs) have shown capabilities beyond existing lightly doped metal–oxide–semiconductor (LDMOS) for high-power applications, and GaN-based power devices ~600 V are currently commercially available. However, emerging areas like charging stations for electric vehicles (EVs) and electric power trains demand ultra-high-power switching >1 kW. Going by what Ga₂O₃ promises, it can be considered as a viable candidate for these emerging as well as existing power electronics areas. Large bandgap-led high critical field of β-Ga₂O₃ ensures superior performance in high voltage rectifiers and E-mode MOSFETs over GaN and SiC. Furthermore, β-Ga₂O₃ HEMTs also outperform GaN HEMTs in terms of X-band RF output power. However, low electron mobility coupled with poor thermal conductivity of β-Ga₂O₃ limits its dc power switching performance and demand device level thermal management. In this paper, we present the evolution of β-Ga₂O₃ HEMTs and overview the high power RF and dc switching performance of the latest reported β-(Al_xGa_1−x)₂O₃/β-Ga₂O₃ MODFETs and AlN/β-Ga₂O₃ HEMTs. These results have been discussed to gauge the capabilities of β-Ga₂O₃ technology and potential applications in RF and high power electronics applications.

In this work, the different figures-of-merit for AlN/β-Ga₂O₃ High Electron Mobility Transistor (HEMT) are computed using TCAD. The first and second-order derivatives of transconductance, output-conductance (g_d), intrinsic-gain (dB), gate-source capacitance (C_gs), gate-drain capacitance (C_gd), transconductance-generation factor (TGF), transconductance-frequency product (TFP), 1-dB compression-point, extrapolated input voltages (VIP₂ and VIP₃), third-order input intercept point (IIP₃), third-order intermodulation distortion (IMD₃), and gain-transconductance frequency product (GTFP) are computed to predict the linearity performance and minimize intermodulation distortion. The present analysis is beneficial for optimizing the device bias point required for RFIC design.

Among various types of biological sensors, the semiconductor biosensors gathered attraction due to their superior advantage in the process of integration, multifunction, and miniaturization. ISFET’s based sensor has been processed for the very same as they deliver faster response, higher sensitivity, higher resolution, and label-free detection. The major drawback of these types of sensors it lacks because of its material degradation of the gate insulators and longer-term drift performance which possess instability in solution. Field-Effect Transistors (FET) based biosensors provide easy signal read-out capabilities, lower detection limit, and higher sensitivity. At the same time, the occurrence of Debye or Charge screening when exposed in high salt concentration suchlike as physiological fluids restrict in ground of clinical applications as assay requirements that includes expansive sample pre-treatment process steps, this technology suffer from noise signals which restrict their detection limit. Upon the introduction of a few external change around surface conditions, i.e., linking of biomolecules in the underlap area of gate region results in significant variation in the piezoelectric-induced carrier density inside channel region of the device results in variation in drain current. Henceforth, comparatively HEMT-based biosensor facilitates higher sensitivity upon immobilization of biomolecules. Therefore these demerits could be overcome by implementation of GaN HEMT biosensor that bears the built-in properties like stability in aqueous solutions, biocompatibility, and are more sensitive to surrounding surface charge as the 2DEG channel concentration at the heterointerface layer which changes due to its existing surface charge variations by capacitive coupling.