Optical Gain and Loss Measurements of Semipolar III-nitride Laser Diodes with ITO/thin-p-GaN Cladding Layers

Abstract

Laser diodes (LDs) based on the group III-nitride material system are forecasted to be the key components of next generation high-intensity white lighting systems [1]. For such systems, LDs offer more power per chip area, much higher spatial brightness, and no efficiency droop above threshold compared to light emitting diodes (LEDs). To meet these expectations, high-power and high-efficiency continuous-wave (CW) operation of a LD is essential. However, to date, InGaN LDs performance is still hampered by a high operating voltage and a poor differential efficiency, which result in lower wall-plug efficiencies (WPE) than InGaN LEDs or other III-V LDs [2], [3]. We have recently demonstrated an enhanced CW performance of blue LDs grown on a semipolar $(20\bar{2}\bar{1})$ n-GaN substrate by replacing part of the resistive p-GaN cladding layer with a tin-doped indium oxide (ITO) layer [4]. With this transparent conductive oxide (TCO) layer, which has a lower modal optical loss than standard metallic p-contacts, and thinned p-GaN layer a very low operating voltage was obtained. Here, we present detailed gain and absorption measurements of these devices. We show a very low optical loss by redesigning the AlGaN electron blocking layer and the p-waveguide doping profile.