Dynamics of GaN band edge photoluminescence at near-room-temperature regime

In this paper we present an approach based on the known radiative recombination rate model to study the dynamics and characteristics of photoluminescence (PL) transitions at room-temperature (RT) regime of GaN thin film. The model states that the dependence of the PL intensity on the laser excitation intensity is I-PL proportional to I-laser(alpha) in which the value of the exponent alpha reveals whether the PL is due to an exciton or band gap recombination mechanism. We elaborated on the model and studied the temperature behavior of the exponent alpha in the range of 180-400 K in order to explore the recombination type for that range. It was found that at the temperature range just below RT similar to 180-270 K the exponent is a slowly increasing function of temperature and has an average value of similar to 1.2, implying a free-exciton recombination mechanism. At similar to 280 K the value of the exponent was found to exhibit a step-function-like behavior with a sharp increase from 1.2 to 1.7. At the temperature range just above RT similar to 300-400 K the exponent was found again to be a slowly increasing function of temperature with an average value of similar to 1.7, implying that at that temperature range the PL involves mainly band gap transitions. From the temperature behavior of the exponent, the activation energy of the free exciton was inferred to be similar to 24 meV.