Internal polarization fields in GaN∕AlGaN multiple quantum wells with different crystallographic orientations

Abstract

We investigate the built-in electrostatic polarization fields in GaN∕AlGaN multiple quantum wells (MQWs) fabricated by the deposition of layers on sapphire substrates with different crystallographic surfaces. The analysis of the photoluminescence (PL) spectra of MQWs grown over (0001) C-plane, (112¯0) A-plane, and (11¯02) R-plane sapphire, as well as the theoretical calculations, revealed the formation of a strong (up to ∼1.7MV∕cm) built-in electrostatic field due to the spontaneous polarization and piezoelectric field in MQWs on C- and A-plane sapphire, whereas there was no indication of polarization in the identical structures grown on R-plane sapphire. The PL dynamics with the increase of excitation can be explained by quantum-confined Stark effect and screening of the built-in electrostatic field due to photoinjected carriers. The internal electrostatic-field-free quantum structures grown on R-plane sapphire may be promising for ultraviolet region optoelectronic applications due to higher emission intensity and stable spectral parameters.