Etch Patterns and the Mechanism of Etching of Germanium by Iodine Vapor

In the reaction between iodine vapor and Ge, the latter is etched away mainly as GeI2 at temperature between 450° and 550°C. The rate of this reaction is not determined by the supply of positive holes. The relative reactivities of three crystallographic surfaces are in the order: {110}>{111}≥{100}, which is the same order as the densities of surface atoms. Thus {100} and {111} planes of slower etching rate are always revealed and pyramidal pits of two-, three- and four-fold symmetries are developed on the surfaces {110}, {111} and {100}, respectively. A triangular pit formed on the (111) surface is regarded as a positive pit and it does not always correspond to a dislocation.