Semipolar group III-nitride distributed-feedback blue laser diode with Indium tin oxide surface grating

Abstract

A novel approach to realize DFB gratings on GaN based laser diodes is presented and single longitudinal mode operation is achieved. For lasers with plasma-etched surface gratings, single mode operation was maintained until 900 mA and the spectral width FWHM was less than 5 pm with a SMSR of more than 29 dB. Moreover, several issues limiting the performance of semipolar III-Nitride DFB laser diodes with the etched grating are also addressed in this work. Besides these first order gratings that were formed by electron beam lithography and shallow plasma etching, an improved grating design based on dielectric teeth imbedded into ITO is described, along with the design’s impact on power and spectral performance. Particularly, by utilizing the HSQ resist, we focus on reducing the high operating voltage by imbedding the grating inside the transparent conductive oxide layer without dry etching. This new design with a non-etched imbedded grating successfully reduces the threshold voltage and achieves an output power of more than 200 mW under pulsed operation from an anti-reflection coated facet.