AbstractIn this study, the photoluminescence (PL) spectra of InGaN/GaN multiple quantum wells (MQWs) grown on sapphire substrates with different orientation at 720°C were investigated at room temperature. Four different substrates were used, which have different surface step structures. Their orientations are: c-plane, a-plane, c-plane with off-set of 2 degree and c-plane with off-set of 6 degree towards a-plane. PL spectra from InGaN/GaN MQWs grown on c-plane substrates showed double-peak emission, while those from the MQWs grown on the others substrates showed single-peak emission. The strongest emission was found on the substrate with off-set of 2 degree towards a-plane. A Shift of PL peak position to long wavelength was observed on the substrates with an off-set angle. Meantime, all emissions were also investigated at different excitation power density. Experimental results indicate that the regular step structure on the substrates can seriously affect the growth of InGaN/GaN MQWs. Segregation effect in InGaN will lead to the high In composition regions (quantum-wire like structure) in the substrates with an off-set angle due to the regular steps on them, as observed by atomic force microscopy. It can be concluded that the surface steps on substrate play an important role in the formation of the In-rich InGaN quantum-wire like structure.
Influence of excitation power and temperature on photoluminescence in InGaN/GaN multiple quantum wells
