Time-resolved photoluminescence from n-doped GaN/Al0.18Ga0.82N short-period superlattices probes carrier kinetics and long-term structural stability

Abstract

Heavily n-doped GaN/Al0.18Ga0.82N short-period superlattices with and without SiN protection layers are studied in spectrally and temporally resolved photoluminescence (PL) experiments. The room-temperature PL from a protected sample displays a nonexponential decay with an initial decay time of 150 ps for low excitation levels and an exponential decay with a time constant of ∼300 ps for higher excitation. The PL decays are governed by nonradiative carrier relaxation into deep defect states which are partially saturated at high excitation densities. PL measurements at low sample temperature reveal a marked influence of carrier cooling on the PL kinetics in a time range up to 50 ps and a significant radiative decay component. SiN coatings are shown to provide long-term stabilization of surface morphology while increasing nonradiative carrier relaxation rates.