Pressure dependence of elastic constants in wurtzite and zinc-blende nitrides and their influence on the optical pressur
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Pressure dependence of elastic constants in wurtzite and zinc-blende nitrides and their influence on the optical pressure coefficients in nitride heterostructures Sławomir P. Łepkowski1 and Jacek A. Majewski2 1 Unipress, Institute of High Pressure Physics, Polish Academy of Sciences, ul. Sokołowska 29, 01-142 Warszawa, Poland 2 Institute of Theoretical Physics, Warsaw University, ul. Hoża 69, 00-681 Warszawa, Poland ABSTRACT We have studied the nonlinear elasticity effects in III-N compounds. Particularly, we have determined the pressure dependences of elastic constants in wurtzite and zinc-blende InN, GaN, and AlN by performing ab-initio calculations in the framework of plane-wave pseudopotential implementation of the density-functional theory. We have found that C11, C12 in zinc-blende phase and C11, C12, C13, C33 in wurtzite phase depend significantly and almost linearly on hydrostatic pressure, for all considered nitrides. Much weaker dependences on pressure have been observed for C44 in both wurtzite and zinc-blende phases. Further, we have examined the influence of pressure dependence of elastic constant on the pressure coefficient of light emission, dE E / dP , in wurtzite and cubic, InGaN/GaN and GaN/AlGaN quantum wells. We show that the pressure dependence of elastic constants results in significant reduction of dE E / dP in nitride quantum wells and essentially improves the agreement between experimental and theoretical values. INTRODUCTION The electronic and optical properties of semiconductor heterostructures depend crucially on the strain arising from the lattice mismatch. Commonly, the strain effects in quantum structures, i.e. quantum wells (QWs), wires or dots (QDs), are described using the standard elasticity theory with elastic constants independent on the strain (so-called linear theory). Nevertheless, there are circumstances where this simple approach is insufficient. Nonlinear elastic properties of GaAs and InAs have recently attracted significant attention. Frogley et al. proposed that pressure dependences of elastic constants in GaAs and InAs are required to explain anomalously small pressure coefficient of band-gap in strained InGaAs layers [1]. Ellaway et al. calculated pressure dependences of elastic constants for InAs and discussed their influence on the properties of InAs/GaAs QDs [2]. They noticed that hydrostatic strain component in the InAs/GaAs QDs is significantly overestimated by calculations based on linear theory of elasticity. For the case of III-N compounds, the nonlinear elasticity effects have not been systematically studied yet. A pioneering paper in this field was published by Kato and Hama who calculated the pressure dependence of elastic compliances for wurtzite AlN [3]. Recently, Vaschenko et al. have used results of these calculations to estimate the influence of the nonlinear elasticity on pressure coefficients of the light emission ( dE E / dP ) in hexagonal GaN/AlGaN QWs [4]. In this work we study the nonlinear elasticity effects in nitride binary compounds.
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