Stable partial dislocation complexes in GaN as charge carrier lifetime modifiers for terahertz device applications by molecular dynamics and first-principle simulations

Abstract

Wurtzite GaN is a promising material for applications in photoconductive THz radiation sources. For this purpose, the photogenerated charge carriers lifetime of the order of tenths of picoseconds is required. A controllable lifetime reduction may be considered to achieve by creating recombination active stable dislocation complexes formed by mobile basal-plane Shockley partial dislocations (PDs). In this work, formation pathways and stability of PD complexes in basal planes of wurzite GaN are studied by molecular dynamics (MD) simulations. The simulations reveal the formation of stable complexes by attractive interaction of two 30{\deg} or two 90{\deg} PDs with opposite Burgers vectors located in consecutive (0001) planes. Ones formed, these complexes change neither their positions, not the atomic configurations during simulated anneal at 1500 K up to the times of 5 ns. The MD results are used as an input for density functional theory calculations to refine the atomic structures of the complex cores and to investigate their electronic properties. The calculated band structures of GaN with 30{\deg}-30{\deg} and 90{\deg}-90{\deg} dislocation complexes indicate localized energy levels in the band gap near the top of the valence band and the conduction band bottom. The calculations of the partial electronic states density confirm the possibility of electron-hole recombination between the states localized at the PD complex cores. These recombination characteristics are distinctly reflected in the calculated absorption spectra. We conclude that creating such PD complexes in required concentration may be a tool for tailoring the recombination properties of wurtzite GaN for THz radiation generation applications.