Strong ultraviolet emission from non-polar AlGaN/GaN quantum wells grown overr-plane sapphire substrates

Abstract

GaN and GaN/Al0.25Ga0.75N multiple quantum wells (MQWs) over c- and r-plane sapphire substrates have been grown by metal-organic chemical vapor deposition. A comparative study of photoluminescence (PL) in GaN epitaxial layers and AlGaN/GaN MQWs on these two types of substrates is reported. At low excitation levels, the measured room temperature PL signal in GaN layers grown over r-plane sapphire was more than order of magnitude lower than in GaN on c-plane substrates. In contrast, the emission intensity from AlGaN/GaN MQWs grown over r-plane substrates was almost 30 times stronger than in the structures grown over c-plane sapphire. Furthermore, with excitation power density up to 1 MW/cm2, the PL peak position for the non-polar MQWs kept completely stable whereas the one for the c-plane structures exhibited a blue shift as large as 250 meV. We attribute this large difference in the ultraviolet emission intensity to the suppression of a strong quantum Stark effect in the AlGaN/GaN MQWs on the r-plane sapphire. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)