Elasticity, band structure, and piezoelectricity of BexZn1−xO alloys

doi:10.1016/j.physleta.2008.01.011

Physics Letters A

Volume 372, Issue 16, 14 April 2008, Pages 2930-2933

https://doi.org/10.1016/j.physleta.2008.01.011 Get rights and content

Abstract

Lattice constants, elasticity, band structure and piezoelectricity of hexagonal wide band gap Be_xZn_1−xO ternary alloys are calculated using first-principles methods. The alloys' lattice constants obey Vegard's law well. As Be concentration increases, the bulk modulus and Young's modulus of the alloys increase, whereas the piezoelectricity decreases. We predict that Be_xZn_1−xO/GaN/substrate ( $x = 0.022$ ) multilayer structure can be suitable for high-frequency surface acoustic wave device applications. Our calculated results are in good agreement with experimental data and other theoretical calculations.

Introduction

In recent years, ternary Be_xZn_1−xO alloys have attracted much attention because their band gaps cover a wide range from 3.4 eV (ZnO) to 10.6 eV (BeO) [1], indicating the potential for development of ZnO-based ultraviolet (UV) LEDs for applications such as solid state lighting and antimicrobial lamps. UV laser diodes based on ZnO/BeZnO films and ZnO/BeZnO-based UV light emitting diodes (LEDs) with an active layer region composed of ZnO/BeZnO quantum wells (QWs) have been fabricated [2], [3]. In addition, ZnO and its ternary alloys, as piezoelectric semiconductors, have been used for high-frequency surface acoustic wave (SAW) devices in wireless communication systems due to their high acoustic velocities and large electromechanical coupling [4], [5]. However, many important parameters such as elastic constants, bulk modulus, Young's modulus, band-gap bowing and piezoelectric coefficients of the alloys are still not available from current experimental data.

BeZnO alloys have advantages over MgZnO alloys [1], [6], [7]. Since BeO and ZnO share the same hexagonal symmetry, phase segregation is not detected in BeZnO alloys. For MgZnO alloys, the band gap will increase to 3.99 eV at room temperature as Mg concentration x increases upward to 0.33, and phase segregation is observed at $x ⩾ 0.36$ , due to different crystal structures and large lattice mismatch between wurtzite ZnO and cubic MgO.

In this work, using first-principles band-structure methods and linear response theory, we have studied equilibrium lattice constants, elasticity, band structure, and piezoelectricity of hexagonal Be_xZn_1−xO ternary alloys. We show that the alloys' lattice constants obey Vegard's law well, and that our calculated lattice constants of the c-axis are in good agreement with experimental data. We also find that the bulk modulus and Young's modulus of the alloys increase and the piezoelectricity decreases with increasing Be concentration. By comparison with the case of wurtzite GaN, we predict that Be_xZn_1−xO/GaN/substrate ( $x = 0.022$ ) multilayer structure can be suitable for high-frequency surface acoustic wave (SAW) device applications.

Section snippets

Computational methods

Our calculations are performed within the local density approximation (LDA) to density functional theory (DFT) as implemented in the plane-wave pseudopotential ABINIT package [8]. The norm-conserving Troullier–Martins pseudopotentials [9] are used and the Zn 3d electrons are explicitly treated as valence electrons. To obtain good convergence, the plane-wave energy cutoff is set to 50 Hartree and the Brillouin zone integration is performed with $6 \times 6 \times 6$ k-mesh points. Dynamical matrices and Born

Results

Table 1 presents our calculated equilibrium lattice constants, elastic constants, bulk modulus, Young's modulus, energy band gap, piezoelectric stress and strain coefficients for pure ZnO and BeO in the wurtzite structure. These results are compared with experimental and other theoretical values [13], [14], [15], [16], [17], [18], [19], [20], [21]. The LDA calculated band gaps are smaller than experimental data due to the well-known LDA band-gap error. All the calculated parameters are in good

Summary

We have studied equilibrium lattice constants, elasticity, band structure and piezoelectricity of hexagonal Be_xZn_1−xO alloys using first-principles methods. We show that the lattice constants of the alloys obey Vegard's law well. We also find that as Be concentration increases, the bulk modulus and Young's modulus increase, whereas the piezoelectricity decreases. The calculated parameters can be useful for band-structure engineering when the alloys are considered for optoelectronic devices and

Acknowledgements

The work is supported by the National Natural Science Foundation of China under Grant Nos. 60325416, 60521001, and 90301007, and by the Foundation of the Chinese Academy of Science.

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Elasticity, band structure, and piezoelectricity of BexZn1−xO alloys

Abstract

Introduction

Section snippets

Computational methods

Results

Summary

Acknowledgements

Comput. Mater. Sci.

Solid State Commun.

J. Phys.: Chem. Solids

Appl. Phys. Lett.

Appl. Phys. Lett.

Appl. Phys. Lett.

IEEE Trans. Ultrason. Ferroelect. Freq. Contr.

IEEE Trans. Ultrason. Ferroelect. Freq. Contr.

Appl. Phys. Lett.

J. Appl. Phys.

Phys. Rev. B

Phys. Rev. B

Rev. Mod. Phys.

Phys. Rev. B

Elasticity, band structure, and piezoelectricity of Be_xZn_1−xO alloys