A Study of the Photoelectrochemical Etching of n-GaN in H3PO4 and KOH Electrolytes

C Heffernan,R P Lynch,D N Buckley

doi:10.1149/2.0082001jss

C Heffernan, R P Lynch + Show 1 more

Open Access

https://doi.org/10.1149/2.0082001jss

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Abstract

We investigated the photoelectrochemical etching of n-GaN in H3PO4 and KOH as a function of electrolyte concentration, potential and light intensity. Etch rates measured by stylus profilometry were compared with coulometric and amperometric values. In both electrolytes, etch rates increased with concentration, reaching a maximum at 3.0 mol dm−3 and decreasing at higher concentrations. The increase in etch rate with concentration of either H3PO4 or KOH reflects the amphoteric nature of gallium and the decrease above 3.0 mol dm−3 is attributed to common-ion effects. Profilometric etch rates were lower than coulometric and amperometric etch rates reflecting formation of a surface film. SEM and profilometry demonstrated that thick surface films are formed at lower concentrations. Etch rates increased linearly with light intensity indicating a carrier-limited etching regime: a quantum efficiency of 57.6% was obtained. At light intensities greater than ∼35 mW cm−2 the etch rates showed evidence of saturation. AFM and SEM images of the etched GaN surfaces showed a distinctive ridge-trench structure with a hexagonal appearance. Photoluminescence spectra of the etched GaN show a significant increase in the defect-related yellow luminescence peak suggesting correlation to the formation of the ridge structures, which may represent dislocations terminating at the surface.

Highlights

Effect of Light IntensityIt can be seen that over most of the range shown, the coulometric etch rate increases with light intensity in a roughly linear manner, similar to the theoretical plots of rlim
Since the pioneering work of Akahashi, Amani and Nakamura,[1,2,3] the development of GaN-based semiconductor technology has revolutionized the lighting industry.[4]
We investigated the PEC etching characteristics of n-GaN in H3PO4 and KOH as a function of electrolyte concentration, applied potential and light intensity

Summary

Effect of Light Intensity

It can be seen that over most of the range shown, the coulometric etch rate increases with light intensity in a roughly linear manner, similar to the theoretical plots of rlim. (a) AFM image of the surface of n-GaN anodized at the half-peak potential Eh in 1.0 mol dm−3 H3PO4 for 500 s under an illumination intensity of 10 mW cm−2; and (b) typical line scan through the image. At light intensities greater than ∼35 mW cm−2 the etch rates show evidence of saturation This indicates a diffusion-limited etching regime where the etch process is limited by the rate at which reactant species in solution can diffuse to and react with the semiconductor surface. ΛeVM,GaN i.e., the quantum efficiency for the photoelectrochemical etching of n-GaN in 1.0 mol dm−3 H3PO4 is estimated to be 57.6%

Morphology of Etched Surface

Anodization in KOH Solutions

Findings

Conclusions