Reduction of Internal Loss and Threshold Current in a Laser Diode with a Ridge by Selective Re-Growth (RiS-LD)

Abstract

The origin of the internal loss in ridge-type laser diodes (LDs) fabricated using selective re-growth is investigated through a systematic device characterization and additional optical measurements. We found that the internal loss of this LD is mainly caused by the absorptive layers at the re-growth boundary and Mg-doped GaN layer. The internal loss can be significantly reduced through a re-design of the LD structure to avoid these absorptive regions by shifting the perpendicular optical field to the n-cladding side. The re-designed LDs had a very low threshold current of 10 mA and superior gain characteristics. These results indicate, that the InGaN-quantum-well (QW) active layer has a large differential gain and fewer non-radiative defects. The fabrication method of this LD, i.e. epitaxial growth on low-dislocation-density GaN substrates combined with a process without dry-etching, is responsible for the high quality of the QWs.