Optical properties of AlGaN/GaN multiple quantum well structure by using a high-temperature AlN buffer on sapphire substrate

We demonstrated highly improved optical properties of the AlGaNGaN multiple quantum well (MQW) structure grown on a GaN layer with significant reduction of dislocations achieved using an AlN buffer directly grown on a sapphire substrate at high temperature, in comparison with the MQW grown using a conventional two-step technique. An enhancement of room-temperature photoluminescence intensity by up to one order of magnitude has been observed, compared with the conventional MQW. Transmission electron microscopy measurements indicated that the dislocation density of the GaN grown using the AlN buffer technique was dramatically reduced. Furthermore, the significantly improved optical properties of this MQW using this AlN buffer technique were also demonstrated by increasing the thickness of the GaN layer underneath, whose crystal quality can be improved by increasing thickness, confirmed by detailed x-ray measurements. Since the technique can significantly improve the optical efficiency in the ultraviolet (UV) spectral region without involvement of any ex situ patterning process, it should be highlighted in the development of high performance UV light-emitting diodes, currently a highly regarded research area.