GaAs wafers, etching

The equipment and the experimental procedures using the C02-methanol medium have already been described in previous papers. . For the photoelectrochemical experiments, a stainless steel pressure vessel was equipped with a 2-cm thick quartz window for illumination, p-type InP and GaAs wafers were cut into ca. 0.4 cm x 0.5 cm electrodes and were mounted using epoxy resin. Ohmic contact was made with successive vapor deposition of Zn (30 mn) and Au (100 nm), which was annealed afterward at 425 C in Ar. A silver wire (0.8 mm dia) was used as a quasi-reference electrode (Ag-QRE, ca. +80 mV vs. SCE). A Pt wire (0.8 mm dia) was used as the counter electrode. The photocathode was etched in hot aqua regia for ca. 5 s before each experiment. The electrolyte solution [3 cm, 0.3 mol dm" tetrabutylammonium perchlorate (TBAP) in CH3OH] was placed in a glass cell liner in the stainless steel vessel. Gases were introduced into the pressure vessel and were left to equilibrate for one hour at the desired pressure (1 to 40 atm). 

FIG. 13 Scanning electron micrograph and profiles of etching pits made on a GaAs wafer as a result of leaving a 25 /rm diameter Pt UME (biased at 1.0 V vs. SCE) above the surface in a 0.02 M ElBr/0.1 M E1C1 solution for different duration. (From Ref. 31.)... 

Fig. 3.6 Cellular dislocation patterns in undoped GaAs crystals revealed by (a) KOH etching of a 4-inch wafer [42],...

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