Dynamics of anomalous temperature-induced emission shift in MOCVD_grown (Al, In)GaN thin films

摘要

We present a comprehensive study of the optical characteristics of (Al, In)GaN epilayers measured by photoluminescence (PL), integrated PL intensity, and time-resolved PL spectrscopy. For npot only INGaN, but also AlGaN epilayers with large Al content, we observed an anomalous PL Temperature dependence: (i) an "S-shaped" PL peak energy shift (decrease-increase-decrease) and (ii) an "inverted S-shaped" full width at half maximum (FWHM) change (increase-decrease-increase) with increasing temperature. Based on time-resolved PL, the S shape (sinverted S shape) of the PL peak position (FWHM) as a function of temperaure, and the much smaller PL intensity decrease in the tem,perature range showing the anomalous emission behavior, we conclude that strong localization of carriers occurs in InGaN and even in AlGaN with rather high Al content. We observed that he following increase with increasing Al content in AlGaN epilayers: (i) a Stokes shift between the PL peak energy and the absorpthion edge, (ii) a redshift of the emission with decay time, (ii) the deviations of the PL peak energy, FWHM< and PL intensity from their typical temperature dependence, and (iv) the corresponding temperature range of the anomalous emission behavior. This indicates that the band-gap fluctuation responsible for these characteristics is due to energy tail states caused by non-random inhomogeneous alloy potential variations enhanced with increasing Al content.