Impact of ITO layer on the spatial optical distribution of semipolar (20-21) InGaN/GaN multiple quantum wells with surface morphology.

Abstract

Textured surface with micro-facets have been widely observed in semipolar and nonpolar III-nitride heterostructures, mainly resulted from the anisotropic growth rate in the growth plane. Polarization and the intensity distribution of surface emissions are both affected by the surface morphology. The indium tin oxide (ITO) layer, serving as the current spreading layer, are usually employed to enhance the current injection efficiency and light extraction efficiency in III-nitride emitters. For semipolar orientation, the introduction of an ITO layer could weaken the anisotropic optical property, especially for the spatial intensity distribution. This paper reports the influence of the ITO layer on the spatial intensity distribution of semipolar (20-21) InGaN/GaN multiple quantum wells. The intensity distribution could be shaped from a rectangular-like pattern to a circular-like pattern with the deposition of an ITO layer. The ITO layer allows more light along the [11-20] direction to emit out at a small angle with respect to the surface normal. By further increasing the ITO thickness, the influence of surface fluctuation of semipolar sample decreases, leading to an improvement in the proportion of the light at small angles and a slight decrease in the overall integrated intensity of whole far field. These results will help pave the way to high-performance semipolar emitters with great potential in general illumination and backlighting.