Photoluminescence excitation spectroscopy of excited states of an asymmetric cubic GaN/Al0.25Ga0.75N double quantum well grown by molecular beam epitaxy

Abstract

Optical transitions involving higher energy levels of cubic AlGaN quantum wells are investigated by means of photoluminescence excitation spectroscopy. An asymmetric cubic GaN/AlxGa1−xN double quantum well (QW) structure with an Al content of x = 0.25 ± 0.03 was grown on a 3C-SiC(001) substrate exploiting radio-frequency plasma-assisted molecular beam epitaxy. The photoluminescence excitation data reveals two emission bands, which are assigned to the first electron and the third heavy hole (e1–hh3) and the second electron and the second heavy hole (e2–hh2) energy level of the wide QW. Besides in the narrow QW no higher energy levels can be observed. The experimental data is in good agreement with theoretical calculations using a Schrödinger–Poisson solver based on an effective mass model (nextnano3). The exciton binding energy was calculated considering the confinement of the QWs and also the energy dependency of the effective mass for excited energy levels.