We present a comprehensive study of the optical characteristics of ${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{N}\mathrm{}$ epilayers $(0\mathrm{}<~x<~0.6)$ by means of photoluminescence (PL), PL excitation, and time-resolved PL spectroscopy. For ${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{N}\mathrm{}$ 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” spectral width broadening (increase-decrease-increase) with increasing temperature. We observed that the thermal decrease in integrated PL intensity was suppressed and the effective lifetime was enhanced in the temperature region showing the anomalous temperature-induced emission behavior, reflecting superior luminescence efficiency by suppressing nonradiative processes. All these features were enhanced as the Al mole fraction was increased. From these results, the anomalous temperature-induced emission shift is attributed to energy tail states due to alloy potential inhomogeneities in the ${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{N}\mathrm{}$ epilayers with large Al content.

• Received 17 May 1999

DOI:https://doi.org/10.1103/PhysRevB.61.7203