Size- and composition-induced band-gap change of nanostructured compound of II–VI semiconductors

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Abstract

We have investigated the joint effect of size- and composition-induced band-gap change of semiconductive nanocompounds from the recently developed bond-order-length-strength (BOLS) correlation mechanism using the approach of local bond average (LBA). An analytical solution has been developed to connect the band-gap energy with the bonding identities of the nanocompounds. Agreement between the model predictions with the available experimental measurements of band-gap change of II–VI semiconductor nanocompounds showed that both the particle size and the composition with alloying effect can be used as factors tuning the band-gap energy, suggesting an effective way to realize the desirable properties of semiconductive nanocompounds.

Graphical abstract

Size dependence of composition-induced band-gap energy of ZnxCd1−xSe.

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Introduction

The semiconductive nanocompounds have been attracted considerable attention for decades due to their unique physical and chemical properties, which make them as the ideal advanced functional materials for nanodevices [1], [2], [3]. Due to the band-gap of semiconductor materials playing a fundamental role in electrical and optical properties, it is important and necessary to study on the band-gap change in order to gain a better understanding for their relevant properties. Up to date, the band-gap of pure nanoparticles has been extensively explored with size in detail [4], [5], [6], [7], [8]. It can be observed that the band-gap displays blue shift with decreasing the size because of surface skin quantum trapping. In most cases, just tuning the size can obtain the demanded band-gap energy. However, to meet wider band-gap, it costs thermal stability and luminescence efficiency of nanometer scale system with decreasing the size, especially the size is less than 2–3 nm [9], [10], [11]. Fortunately, nanosemiconductor alloys not only have the basic optical properties as pure semiconductor nanoparticles but also have their own superiorities such as high luminescence, much more stability and a single system with multiple characteristic. That is why the study of alloy is beginning to rise from experimentally [12], [13], [14], [15], [16], [17], [18], [19], [20], [21] to theoretically. A large number of experiments have been reported that the band-gap of homogeneous alloy Eg(x, D) express the nonlinear function with composition x (the molar ratio). Several models with regard to composition-induced band-gap change of homogeneous nanostructure alloys have been developed, such as [10], [11], [19], [20]:Eg(x,D)=xEg(1,D)+(1-x)Eg(0,D)-bx(1-x)(empirical)xEg(1,D)+(1-x)Eg(0,D)(Vegard et al.)1/(xEg(1,D)+1-xEg(0,D))(Fox)xEg(1,D)+(1-x)Eg(0,D)+Ω(x,D)x(1-x)(Zhu et al.)where the coefficient b represents the nonlinear effect resulting from the anisotropic nature of binding, which is difficult to measure in experiment. Although no adjustable parameters are used in Vegard’s law and Fox’s model, the former does not describe well the relationship between the band-gap and the composition, and the latter could not reproduce the measured data reasonably if the atomic interaction energy of the alloy components is strong. Strikingly, Zhu et al. [10] recently proposed the model based on Vegard’s law which performs better than the others as mentioned above because they have considered the size-dependent atomic interaction bond energy Ω(x, ). However, among these theoretical methods above, the atomistic origin between the band-gap and the bonding identities of nanocompounds is not properly addressed. Therefore, for this reason, in this contribution, we present an atomistic insight into the size dependence of the composition-induced band-gap change of II–VI semiconductor nanocompound based on the recently developed bond-order-length-strength (BOLS) correlation mechanism using the approach of local bond average (LBA) [6], [22]. Our theoretical results revealed the composition-dependence band-gap yields a downward bowing behavior arising from inter-atomic interaction of alloy components and the size-dependent band-gap expansion displays a rising trend because of the broken bond-induced lattice strain and quantum trapping in the relaxed surface region. It is also found that the size and composition with alloy effect can tune the band-gap energy, which suggests an effective way to reach the desirable electrical and optical properties.

Section snippets

Principle

The BOLS correlation mechanism [6], extending from the Goldschmidt’s and Pauling’s considerations [23], [24] to energy domain, indicates the physical origin of the shape- and size-dependence of bond length, bond nature and bond strength of nanosolids. It elucidates well that band-gap expansion originates from the coordination-imperfect-induced bond contraction spontaneously and the associated with bond energy rising at the curved surface of a nanosolid. According to the nearly-free-electron

Results and discussion

To investigate the impacts of size and composition on band-gap energy of bulk and nanosemiconductor compounds, we have compared with the band-gap of them among the theoretical methods in terms of Eq. (3) or Eq. (4) and the available experimental results. The calculation parameters are given in Table 1. Fig. 1 shows the theoretical predictions and the experimental measurements for the Eg(x, ∞) function of bulk semiconductor alloys (CdSxSe1−x, ZnxCd1−xSe, ZnxCd1−xS and CdTexSe1−x). Clearly, the

Conclusion

In summary, the band-gap energy change of nanocompounds is well addressed based on the BOLS correlation mechanism, which enable us to understand the composition- and size-dependent band-gap energy in nanostructure alloy involving CN-imperfection-enhanced bond strength at a surface with no assumption or freely adjustable variables. The results reveal the variable trend of band-gap of both the bulk and the nanometer scale with the size and the composition are similar, such as a downward bowing

Acknowledgements

Project supported by the Major Research plan of the National Natural Science Foundation of China (Grant Nos. 10747129, 10772157 and 90606001), the National Fundamental Research Program of China (Grant No. 2007CB925204), the Natural Science Foundation of Hunan Province, China (Grant No. 07JJ3114) and Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20050532013).

References (37)

  • C.Q. Sun

    Prog. Solid State Chem.

    (2007)
  • D.S. Sutrave et al.

    Mater. Chem. Phys.

    (2000)
  • A.H. Ammar

    Vacuum

    (2001)
  • A.R. Clapp et al.

    J. Am. Chem. Soc.

    (2004)
  • M.J. Bowers et al.

    J. Am. Chem. Soc.

    (2005)
  • A. Rizzo

    Appl. Phys. Lett.

    (2007)
  • S. Kan et al.

    Nature

    (2003)
  • G. Ouyang et al.

    Appl. Phys. Lett.

    (2006)
  • R. Koole et al.

    Small

    (2008)
  • X.Y. Lang et al.

    Nanotechnology

    (2008)
  • X. Zhong et al.

    J. Am. Chem. Soc.

    (2003)
  • Y.F. Zhu et al.

    Adv. Funct. Mater.

    (2008)
  • C.C. Yang et al.

    J. Phys. Chem. C

    (2008)
  • D.V. Petrov et al.

    J. Phys. Chem. B

    (2002)
  • R.E. Bailey et al.

    J. Am. Chem. Soc.

    (2003)
  • C.X. Shan et al.

    Appl. Phys. Lett.

    (2005)
  • Y. Liang et al.

    J. Phys. Chem. B

    (2005)
  • Y. Li et al.

    Adv. Funct. Mater.

    (2006)
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