Abstract
The density functional perturbation theory (DFPT) is employed to study the structure, optical phonon modes and dielectric properties for wurtzite GaN and AlN under hydrostatic pressure. In order to calculate accurately the Born effective charges and high frequency dielectric tensors, we utilize two sum rules to monitor this calculation. The calculated optical phonon frequencies and longitudinal-transverse splitting show an increasing with pressure, whereas the Born effective charges and high frequency dielectric tensors are found to decrease with pressure. In particular, we analysed the reason for discrepancy between this calculation and previous experimental determination of pressure dependence of the LO-TO splitting in AlN. The different pressure behavior of the structural and lattice-dynamical properties of GaN and AlN is discussed in terms of the strengths of the covalent bonds and crystal anisotropy. Our results regarding dielectric Gruneisen parameter are predictions and may serve as a reference.
Highlights
The group-III nitrides GaN and AlN are currently being actively investigated in view of their promising potential for short-wavelength electroluminescence devices and high-temperature, high-power, and high-frequency electronics [1]-[5]
An important motivation for high-pressure investigations stems from the fact that group-IIInitride layers are commonly subjected to large built-in strain since they are often grown on different substrates
The splitting of the optical phonon modes is determined by two parameters, Born effective charge of the lattice ions and the screening of the Coulomb interaction, which depends on the electronic part of the dielectric constant in the phonon frequency regime
Summary
The group-III nitrides GaN and AlN are currently being actively investigated in view of their promising potential for short-wavelength electroluminescence devices and high-temperature, high-power, and high-frequency electronics [1]-[5]. Afterwards, Goñi et al [8] compared the pressure dependence of the Raman-active modes in GaN and AlN with ab initio calculations and found a small but increasing LO-TO (E1) splitting under pressure. Francisco et al studied the optical phonon modes and pressure dependences of AlN by means of ab initio lattice dynamical calculations, but being a increase of the LO-TO splitting for both A1 and E1 modes. It will study pressure dependence of zone-center optical phonon modes and the LO-TO splitting of both the A1 and E1 modes It will calculate and discuss the pressure dependence of Born effective charge tensors Z ∗ and the high frequency dielectric tensor ε∞.
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