Effect of a patterned sapphire substrate on indium localization in semipolar (11-22) GaN-based light-emitting diodes

Abstract

We have demonstrated the control of arrowhead-like surface structures in a semipolar (11-22) GaN film grown on a patterned sapphire substrate (PSS). The PSS can reduce the anisotropic crystallographic tilts of the semipolar (11-22) GaN film compared with a normal sapphire substrate (NSS). Semipolar (11-22) GaN-based light-emitting diodes (LEDs) grown on the PSS generated higher optical output power than the NSS. In addition, two emission peaks were observed for the semipolar (11-22) GaN-based LEDs grown on both substrates. However, as the injection current increased, the longer-wavelength emission peak of the LED grown on the NSS remained strong; meanwhile, the shorter-wavelength emission peak of the LED grown on the PSS was dominant over the longer-wavelength emission. Based on micro-electroluminescence images, we found that a longer-wavelength emission could be initiated at the front edge of the arrowhead-like surface structure; this emission expanded to the side edge regions of these structures as the injection current increased. Based on these results, we propose that using a PSS could decrease the number of arrowhead-like surface structures of semipolar (11-22) InGaN quantum wells; this further leads to a reduction in the strong indium localization produced at the arrowhead-like surface structure.