Optical detection of nonradiative recombination centers in AlGaN quantum wells for deep UV region

By superposing a chopped below-gap excitation (BGE) light on a cw above-gap excitation and observing the intensity change of photoluminescence (PL) due to the BGE, we clarified a distribution of nonradiative recombination (NRR) centers in AlGaN multi-quantum well (MQW) structures for the wavelength region of deep ultraviolet (UV). The decrease in band-edge PL peak intensity at 10 K exemplified the presence of a pair of NRR centers in AlGaN well layers whose transition energy corresponds to that of the BGE. The BGE power dependence of the normalized PL intensity showed a quenching saturation due to trap-filling effect of electrons in one of the centers which were activated by the BGE. The BGE energy dependence of the normalized PL intensity revealed that the optical activation energy of the dominant NRR process via these trap states in the AlGaN MQW is around 1.17 eV. The purely optical scheme of detection enables us to obtain clues for identifying defect levels in DUV region and eliminating them during growth process without any preparation of electrodes. (C) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim