Etching of the InP(0 0 1) surface by chlorine: quantum chemical calculations to the reaction mechanisms

Using molecular models for local surface structures and the density functional method the energies and equilibrium geometries are computed for probable local chemisorption structures of the system Cl2 + InP(0 0 1). Calculated chemisorption and desorption energies and related barrier heights allow to develop reaction mechanisms and to determine the rate-limiting steps for the reactive etching. Furthermore, the stable surface structures and the reaction products are found out. The reaction behaviour at steps as well as the influence of the chemisorption at neighbour positions are investigated. Two regimes are found out, which are consistent with the frequently discussed α- and β-state: At low temperatures and high Cl2 concentrations the indium and phosphorus atoms are removed as InCl3 as well as PCl3 and, partially, as InCl as well as PCl2 (α-state). At higher temperatures and low chlorine availability, InCl and P2 (P4) are the main products (β-state). The rate-limiting steps are the PCl3 desorption for the α-state (24 kcal/mol) and the P2 desorption for the β-state (37 kcal/mol). The steady state etching is only possible under higher temperatures by reason of hindered transport of the etch gas and the products under low temperatures caused by a relatively stable corrosion phase composed of InCl3.