Dynamics of anomalous optical transitions in AlxGa1-xN alloys

We present a comprehensive study of the optical characteristics of AlxGa1-x N epilayers (0 less than or equal to x less than or equal to 0.6) by means of photoluminescence (PL), PL excitation, and time-resolved PL spectroscopy . For AlxGa1-xN with large Al content, we observed an anomalous PL temperat ure dependence: (i) an "S-shaped'' PL peak energy shift (decrease-increase- decrease) and (ii) an "inverted S-shaped" spectral width broadening (increa se-decrease-increase) with increasing temperature. We observed that the the rmal decrease in integrated PL intensity was suppressed and the effective l ifetime was enhanced in the temperature region showing the anomalous temper ature-induced emission behavior, reflecting superior luminescence efficienc y by suppressing nonradiative processes. All these features were enhanced a s the Al mole fraction was increased. From these results, the anomalous tem perature-induced emission shift is attributed to energy rail states due to alloy potential inhomogeneities in the AlxGa1-xN epilayers with large Al co ntent.