The mechanism and influence of photogalvanic interactions during localized photoetching of III-V semiconductors have been investigated. Starting from the cyclovoltammograms and etching kinetics in the dark and under uniform illumination, the chemistry of the mixed dark/illuminated system is discussed. Both in terms of current-potential curves and of band-energy diagrams, it is demonstrated how a geometrical separation of partial hole and electron currents can lead to the strong enhancement of etch rates under localized illumination. Some illustrative experiments are discussed, quantitatively. In the present work GaAs in acidic H202 and $2082-solutions are used as model systems, but in addition some results from other III-V compounds and etchants are presented.
A novel technique is described with which the etching of p‐type semiconductors in solution can be affected by the use of light. The method is based on the principle that illumination of a part of the surface leads to enhanced dissolution in the non‐illuminated areas. Effective separation of photogenerated charge carriers is obtained by employing a two‐compartment cell. In this cell, the dark and illuminated surfaces can be exposed to solutions of a different composition and pH. The choice of the oxidizing agent in this system is important: its reduction should not involve free carriers in the semiconductor bands in the dark, whereas it should do so under illumination. For
normalGaAs
,
H2O2
in
H2SO4
, and for
normalInP
,
Br2
in
normalHBr
, are shown to be suitable. Ratios of etch rates under illumination and in the dark of the order of 103 and higher are demonstrated.
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