On intrinsic Stokes shift in wide GaN/AlGaN polar quantum wells

TL;DR

This paper investigates the intrinsic Stokes shift in wide GaN/AlGaN polar quantum wells, revealing how built-in electric fields affect optical transitions and spectra interpretation, with implications for understanding their electronic properties.

Contribution

It provides a detailed comparison of ER and PL spectra with band structure calculations, highlighting the role of electric fields in optical transition selection rules and identifying the intrinsic Stokes shift.

Findings

PL shows ground state emission, ER dominated by excited states

Built-in electric field breaks selection rules, enabling many optical transitions

Intrinsic Stokes shift exists even in wide, homogeneous GaN/AlGaN QWs

Abstract

The interpretation of electromodulated reflectance (ER) spectra of polar quantum wells (QWs) is difficult even for homogeneous structures because of the built-in electric field. In this work we compare the room-temperature contactless ER and photoluminescence (PL) spectra of polar GaN/AlGaN QWs with the effective-mass band structure calculations. We show that the emission from the ground state transition is observed in PL but the ER is dominated by transitions between excited states. This effect results from the polarization-induced built-in electric field in QW that breaks the selection rules that apply to square-like QWs, allowing many optical transitions which cannot be separately distinguished in the ER spectrum. We develop the guidelines for the identification of optical transitions observed in PL and ER spectra. We conclude that an intrinsic Stokes shift, i.e., a shift between emission and absorption, is present even for homogeneous GaN/AlGaN QWs with large width, where the electron-hole wavefunction overlap for the fundamental transition is weak.