Etch Pits and Polarity in CdTe Crystals

Abstract

Two types of etch pits in cadmium telluride have been observed. The etchants used are nitric acid solutions of potassium bichromate which also contain silver ions of various concentrations. The etch pits resulting from etch (EAg‐1) grow into a tetrahedral shape bounded by the crystallographic habit planes and reveal geometrical polarity on the (111) and (1̄1̄1̄) surfaces. Another type of etch pit is formed at a different point from that of the pit with EAg‐1 by the modified etch (EAg‐2), which has increased content of Ag⁺ ion. The two types of etch pits, with EAg‐1 and with EAg‐2, are believed to be associated with Cd and Te edge dislocations. The dissolution rate and its selectivity to the constituent elements in cadmium telluride is controlled electrochemically by the variation of the Ag⁺ ion concentration of the etching solution. The structure of the twin boundary is also studied by etching and back Laue techniques.