On-wafer fabrication of cavity mirrors for InGaN-based laser diode grown on Si

Junlei He,Huaibing Wang,Yu Zhou,Yaozong Zhong,Masao Ikeda,Qian Sun,Shuming Zhang,Jianxun Liu,Hongwei Gao,Rui Zhou,Hui Yang,Yingnan Huang,Jin Wang,Meixin Feng

doi:10.1038/s41598-018-26305-8

Abstract

Direct bandgap III-V semiconductor lasers grown on silicon (Si) are highly desired for monolithic integration with Si photonics. Fabrication of semiconductor lasers with a Fabry–Pérot cavity usually includes facet cleavage, however, that is not compatible with on-chip photonic integration. Etching as an alternative approach holds a great advantage in preparing cavity mirrors with no need of breaking wafer into bars. However, gallium nitride (GaN) sidewalls prepared by dry etching often have a large roughness and etching damages, which would cause mirror loss due to optical scattering and carrier injection loss because of surface non-radiative recombination. A wet chemical polishing process of GaN sidewall facets formed by dry etching was studied in detail to remove the etching damages and smooth the vertical sidewalls. The wet chemical polishing technique combined with dry etching was successfully applied to the on-wafer fabrication of cavity mirrors, which enabled the realization of room temperature electrically injected InGaN-based laser diodes grown on Si.

Highlights

Silicon photonics call for electrically injected semiconductor laser diodes (LDs) as on-chip light sources[1,2,3]
The morphology evolution of gallium nitride (GaN) m- and a-plane sidewalls during tetramethyl ammonium hydroxide (TMAH) wet chemical polishing
Before using the etching method to fabricate the cavity mirrors for InGaN-based LDs grown on Si, we study the morphology evolution of GaN m- and a-plane sidewalls during TMAH wet chemical polishing using 3-μm-thick crack-free high-quality GaN film

Summary

Results and Discussion

The morphology evolution of GaN m- and a-plane sidewalls during TMAH wet chemical polishing. The above observations clearly indicate that an electrically injected lasing was achieved at room temperature for the InGaN-based LD grown on Si, and that the TMAH wet chemical polishing of the as-etched cavity mirrors can significantly reduce the threshold current. We have developed an on-wafer fabrication technique for forming the cavity mirrors of InGaN-based lasers grown on Si. After a sufficient chemical polishing by TMAH wet solution, the as-etched GaN m-plane facets become smooth and vertical, and the ICP etching damages can be removed simultaneously. The result is the realization of room temperature electrically injected InGaN-based LDs grown on Si, which as on-chip light sources can be better monolithically integrated on Si than the conventional lasers prepared by facet cleavage

Methods

Author Contributions

Additional Information