Crack-free GaN-based ultraviolet multiple quantum wells structures grown on AlN/2° misoriented sapphire template

Highlights: •A method of growing crack-free multiple quantum wells (MQWs) on AlN is presented. •The AlN template was grown on vicinal 2° misoriented sapphire substrate. •The MQWs on AlN has an improved crystalline quality. •The MQWs on AlN has a larger internal quantum efficiency. -- Abstract: An approach of growing crack-free GaN-based InGaN-multiple quantum wells (MQWs) with emission at 365 nm on AlN template, instead of conventional GaN template, by metal-organic chemical vapor deposition is presented. The AlN template used here was grown on the vicinal 2° misoriented sapphire substrate. Scanning electron microscopy and atomic force microscopy investigation show that cracks do not form in the MQWs structure grown on an AlN template. The full width at half maximum of high resolution X-ray diffraction rocking curve of the n-Al_0.02Ga_0.98N buffer decreases dramatically when grown on an AlN template, indicating improved crystalline quality. Moreover, Photoluminescence spectra show that the employment of AlN/2° misoriented sapphire template is beneficial to internal quantum efficiency and its thermal stability. Finally, transmission election microscopy reveals a prominent reduction of dislocation density at the undoped GaN/AlN interface.