Photoluminescence characteristics of InGaN light-emitting diodes grown on (0001) and sapphire substrates

The temperature, excitation power and polarization dependence of ultraviolet (UV) photoluminescence (PL) of InGaN/AlGaN light-emitting diodes (LEDs) grown on (0001) and (1120) sapphire substrates were investigated. It appears that the LEDs grown on (1120) sapphire substrates show higher integrated luminescent efficiency than that of the LEDs grown on (0001) sapphire substrates. From the experimental data, it is believed that, for the InGaN LEDs having reduced InN molar fraction in the InGaN well layer, the PL characteristics are determined by the competition between the QW (or QD) radiative recombination, spatially localized radiative recombination and defect-induced nonradiative recombination. According to the results of polarization dependent edge-emitting PL measurements, the LEDs grown on (1120) sapphire substrates were found to exhibit a QW-like behaviour, while the LEDs grown on (0001) sapphire substrates were observed to show a mixed QW/QD-like behaviour. The polarization dependent edge emitting PL measurement is considered to be a highly sensitive technique for the characterization of the nanostructures of InGaN MQW LEDs.