Full optical phonon states and their dispersive spectra of a wurtzite GaN/AlGaN superlattice: Quantum size effect

Abstract

AbstractThe polar optical phonon states of four types of phonon modes including the interface optical (IO) modes, the propagating (PR) modes, the quasi‐confined (QC) phonon modes in well‐layer material (QCw), and the QC phonon modes in barrier‐layer material (QCB) in a wurtzite GaN/AlxGa1–xN superlattice (SLs) are investigated within the dielectric continuum model framework. The analytical phonon states of the four types of modes and their dispersive equations in the wurtzite GaN/AlxGa1–xN SL structures are obtained. Numerical calculations on the dispersive spectra of phonon modes and the quantum size effect are performed for a wurtzite GaN/Al0.15Ga0.85N SL. Results reveal that dispersive curves of phonon modes in SLs form a series of frequency bands. The behaviors of QCw modes reducing to PR and IO modes are observed clearly. With the increase of well‐layer GaN width d1 of the SLs, the dispersion of the QCB modes become weaker and weaker, and their frequency bands become narrower and narrower. But the PR, IO, and the QCw phonon modes become more dispersive, and the frequency bands of these modes become wider and wider as d1 increases. The present theoretical scheme and numerical results are quite useful for analyzing the dispersive spectra of full phonon modes and their polaronic effect in wurtzite GaN/AlGaN SL structures.