A COMPARISON OF THE ELECTROCHEMICAL-BEHAVIOR OF ILLUMINATED N-INAS AND OTHER III-V SEMICONDUCTORS IN CONCENTRATED NITRIC-ACID

The reaction kinetics of illuminated n-InAs etched in nitric acid have been studied. Nitrogen dioxide was observed to evolve when the test sample was immersed in the acid solution. The dissolution rates of InAs, determined by the inductively coupled plasma (ICP) technique, were high. The nitrogen dioxide evolution reaction is believed to be an autocatalytic process which is followed by nucleophilic attack of the InAs electrode in which the surface oxides are etched away. Nitrite is an essential catalyst for the reaction and is also involved in the formation of an indium complex. The possible role of the energy levels at the semiconductor/HNO3 interface are discussed in an attempt to explain the widely different reactivities of the four III-V semiconductors InP, GaAs, GaP, and InAs. The very much higher dissolution rate of InAs was discussed in terms of (i) the adequate overlap of the distribution function of the oxidizing agent (nitrate) with the InAs valence band, and (ii) the energetic instability of the electrons in the In-As bonding orbitals. In contrast, the opposite is true in the case of the other III-V materials. In the latter materials, electron transfer can occur across the semiconductor/electrolyte interface only via low density surface states within the bandgap.