Optic and Acoustic Phonons in Strained Hexagonal GaN/AlGaN Multilayer Structures

Abstract

The effects of the layer thickness and alloy composition on the Raman spectra of hexagonal GaN/AlxGa1—xN multilayer structures have been investigated. Our findings show that the A1(TO) optic mode can be regarded as propagating through the structure, whereas other optic modes are confined to the GaN or AlxGa1—xN layer. We report the first observation of folded acoustic modes in short‐period GaN/AlxGa1—xN superlattices. The dispersion of the LA phonon branch was determined by using different Raman scattering configurations. The sound velocity for GaN/AlxGa1—xN SL with Al content x = 0.28 was found to be 8410 m/s.

Properties of GaN and related compounds studied by means of Raman scattering

“…More recently, Davydov et al examined several GaN/AlGaN SLs, and reported that only the A 1 (TO) mode is propagating, while other optical modes are confined. Folded acoustic phonon modes were also clearly observed [99]. Strain effects have been investigated in SLs of GaN/AlN [100] and GaN/AlGaN [99].…”

“…Folded acoustic phonon modes were also clearly observed [99]. Strain effects have been investigated in SLs of GaN/AlN [100] and GaN/AlGaN [99].…”

Recent progress in group III-nitride nanostructures: From materials to applications

“…Two-mode behavior of the E 2 (high) Raman phonon in ternary alloyed nitride NWs was classified. The first-order Raman spectra of the alloyed ternary crystals comprised both AlNand GaN-like vibrational modes in AlGaN NWs,[187] as shown in Figure12(d), of which the wavenumbers of both E 2h modes are peaked in between those of pure GaN and AlN. With the increase of Al content (x), both the AlN-and GaN-like E 2h modes shift to low frequency.Similar behavior can be observed in A 1 (TO), E 2 , and A 1 (LO) modes of InN in In-richIn 1-x Ga x N sample and the E 2 (high) and A 1 (LO) modes of GaN in the Ga-rich Ga 1-x In x N NWs[145], as provided in Figure12(e).…”