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

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.

Optimization of Mesa Etch for a Quasi-Vertical GaN Schottky Barrier Diode (SBD) by Inductively Coupled Plasma (ICP) and Device Characteristics

“…The sidewall was near 90 • steep and the surface was smoother after TMAH wet treatment. This is due to the sidewall being etched preferentially in anisotropic wet etching solution [43][44][45].…”

Revealing the Role of Sidewall Orientation in Wet Chemical Etching of GaN-Based Ultraviolet Light-Emitting Diodes

“…Without the aid of UV light irradiation or bias voltage, the wet etching only selectively occurs at semi-polar and non-polar planes of GaN, which would not prohibit the hydroxide ions from accessing the Ga atom [22,23,24]. It was also reported that the wet etching rate of GaN is dependent on the crystallographic planes of GaN [25,26,27]. Thus, the anisotropic wet etching of GaN generally leads to peculiar textures at different surfaces, such as trigonal prisms and hexagonal pyramids, by exposing specific crystallographic planes [21,28,29].…”

“…In the mass-production of LEDs, the LED chips are commonly cut into cuboid geometry by laser scribing without considering the sidewall orientation, which means that the exposed crystallographic planes are indecisive. Some researchers have reported that the surface morphologies are varied at different sidewalls for the striped GaN pattern and cuboid geometry LED chips after wet etching [20,25,27]. However, it is unknown whether the sidewall orientation has influence on the optical and electrical performance of LEDs with chemical etching treatment.…”

Narrow-Linewidth GaN-on-Si Laser Diode with Slot Gratings

“…The statistical results are presented in Supplementary Figure S2. The change in the morphology of the cavity facets and slot sidewalls caused by the TMAH etching originated from the anisotropic electrochemical properties of various crystallographic planes, which has been observed and explained in our previous work [44]. During the TMAH wet etching, Ga atoms in the m-plane surface with positively charged dangling bonds attract and react with OH − in the TMAH solution, producing GaO x , which dissolves in the solution.…”