True green semipolar InGaN-based laser diodes beyond critical thickness limits using limited area epitaxy

Abstract

Semipolar oriented laser diodes (LDs) have fundamental advantages over c-plane oriented LDs, however, the thickness and composition of InGaN waveguiding layers and AlGaN cladding are limited by the onset of stress relaxation via threading dislocation glide on the c-plane slip system. Limited area epitaxy minimizes misfit dislocation (MD) formation by preventing pre-existing TDs from entering a patterned mesa. We examine the effects of mesa height and facet evolution for LAE grown strained layers. Significant MD formation was suppressed by at least a factor of four for Al0.1Ga0.9N/GaN superlattices, enabling AlGaN-clad structures similar to those used in c-plane LDs. We then demonstrate AlGaN-clad blue (456 nm) LDs with threshold current density (Jth) of 4.5 kA/cm2 and GaN-clad true green (523 nm) LDs with Jth of 12 kA/cm2. TEM measurements of the green LD confirm reduction of MD densities with reduction of MD run length. LAE is effective for improving the optical confinement factor of semipolar LDs and offers a glimpse of the design space that may soon be available using low TD density bulk GaN substrates.