Nonradiative recombination centers in deep uv-wavelength algan quantum wells detected by below-gap excitation light

Nonradiative recombination (NRR) centers in AlGaN multiple quantum well samples, grown on sapphire substrate at two different growth temperatures by the MOCVD technique, have been studied by using below-gap excitation (BGE) light in photoluminescence (PL) measurements at about 25 K. The PL intensity decreased by the superposition of BGE light of energies between 0.93 and 1.46 eV over above-gap excitation light of energy 4.66 eV. This is explained by a two-level model based on Shockley-Read-Hall statistics. The model indicates the presence of a pair of NRR centers in both samples, which are activated by the BGE. The degree of PL quenching for the sample grown at 1140 °C is higher than that of the sample grown at 1180 °C for BGE energies 0.93, 1.17, and 1.27 eV. The density ratio of 1.5, for the BGE energy of 1.27 eV, was obtained from a qualitative simulation. This result implies that a slight difference in growth conditions changes defect densities.