THE DEPENDENCE OF THE ETCHING PROPERTIES OF ILLUMINATED INAS, GAP, AND OTHER III-V SEMICONDUCTORS IN CONCENTRATED HCL SOLUTIONS ON THE FORMATION OF CHLORO COMPLEXES

The influence of complex formation on the etching characteristics of illuminated InP and GaAs in HCl solutions has previously been considered. To further examine the effect of complex formation, the etching behavior of InAs and GaP in HCl under illumination has been investigated in this work. In the case of InAs, the dissolution rate in HCl solutions increase dramatically with an increase in acid concentration above 6M, and the In(I)-In(III) mixed valence chloro compounds were found on the oxidized surface. In contrast, the dissolution of GaP was severely restricted, even in the most acidic solutions, and no gallium chloro compounds were formed. The kinetics of the semiconductor electrode process were shown not to be important enough to explain the lack of reactivity in GaP and GaAs. Speculation on the role of the univalent In and Ga chloro compounds and the driving force of the electron transfer between these intermediates and the redox systems, including electron/hole couple, are given and evaluated. The experimental results obtained with these four III-V compounds are in complete agreement with the mechanistic concepts presented in this paper. The differences in their reactivities can be interpreted in terms of the differences in the stabilities of InCl and GaCl which, in turn, determine whether or not the nucleophilic attack by Cl- can occur.