Hole transport equation analysis of photoelectrochemical etching resolution

Abstract

A theoretical model that predicts the spatial resolution for grating formation on n-type semiconductors by photoelectrochemical etching has been developed. The ratio of the amplitude of the grating to the average depth etched by a sinusoidal spatial variation of light intensity was determined from a model that takes into account the drift and two-dimensional diffusion of the photogenerated holes and their rate of reaction at the surface. Experimental measurements of the growth of gratings agree with the predictions of the theory for the dependence on the period of the grating, the carrier concentration of the semiconductor, and the wavelength of the light. Fitting the experimental data to the theory provides a novel method for determining the reaction velocities of the decomposition reaction in different electrolytes. The theory predicts that large improvements in the resolution would be possible if electrolytes giving higher reaction velocities could be found.

Photoelectrochemical Etching of GaAs / AlGaAS Multilayer Structures

“…Important applications of lightinduced etching in device fabrication have been demonstrated for microlenses, waveguides and waveguide devices, diffraction gratings, lasers and through-wafer via formation. [9][10][11][12][13][14][15][16] Although the electrochemistry of semiconductors under illumination is well understood, ~7' 18 and photoelectrolysis, 19 photovoltaic behavior, 2~ photocorrosion and photodecemposition, ~1 as well as light-sensitive etching of semiconductors [22][23][24] have been studied in great detail, only a few reports of wet-chemical etching of heterostructures are available, and these reports deal almost exclusively with the selectivity of the process for layers of different semiconductors.2 '14'25 -28 In addition, there appears to be no clear understanding of the electrochemical behavior of heterojunctions in contact with an etching electrolyte. In particular, the electrochemistry is complicated not only by the different materials on both sides of the junction but also by the effects of interfacial mobile charge and potential barriers.…”

Propagation of Nanopores and Formation of Nanoporous Domains during Anodization of n-InP in KOH

“…However, when holes may diffuse parallel to the surface of the semiconductor, the electrochemical etching reaction may occur some distance from the pore tip where the holes are created and, as discussed below, this may lead to CO pore formation. Such diffusion of holes from their points of generation to the points where etching ultimately occurs has been reported 25 for photoanodic etching of n-type III-V semiconductors where etching was observed to extend beyond the illuminated region.…”

Fringe stabilization and depth monitoring during the holographic photoelectrochemical etching of n-InP (100) substrates

“…7 In practice, however, one of the major factors which limits the contrast and resolution of direct PEC etching is drift of the projected holographic grating due to vibra-tions and thermal gradients in the holographic setup or thermal and concentration gradients in the electrolyte. 7 In practice, however, one of the major factors which limits the contrast and resolution of direct PEC etching is drift of the projected holographic grating due to vibra-tions and thermal gradients in the holographic setup or thermal and concentration gradients in the electrolyte.…”