MOCVD growth and optical investigation of the AlInGaN quaternary system

By means of a vertical low-pressure metalorganic chemical vapor deposition, high quality Al_x1In_y1Ga_1-x1-y1N: barrier/Al_x2In_y2Ga_1-x2-y2N: well (x1 > x2 and y1 < y2) multiple quantum well structures (MQWs) with the emission wavelengths at less than or equal to 350 nm have been successfully grown on sapphire substrates. The photoluminescence (PL) intensity at room temperature is dramatically enhanced by about two orders of magnitude compared to AlGaN/GaM MQWs with a similar emission wavelength. Furthermore, the PL intensity approaches that of InGaN/GaN MQWs, where the stimulated emission has been easily observed under optical pumping at room temperature. This means that AlInGaN MQW has potential to be used as the active region for ultra-violet light-emitting diode (LED) or laser diode (LD) with an emission wavelength down to 350 nm, and could have a similar performance to InGaN/GaN-based LEDs or LDs. The temperature dependant PL measurement indicates that there exists a strong exciton-localization-effect in AlInGaN MQW, which could be attributed to the greatly enhanced PL intensity. In addition, the influence of growth condition on the optical properties of AlInGaN are discussed, focusing on the effect of the growth pressure.