Digital Electrochemical Etching of Compound Semiconductors

The principles for an electrochemical digital etching method for compound semiconductors are described and initial results reported. The method is designed to allow atomic level control over the etching process, resulting in the removal of a bilayer of the compound for each cycle. An atomic layer of one element is removed at one potential and then an atomic layer of the second element is removed at a second potential to complete one cycle. The results reported here are for the etching of CdTe. For CdTe, Te is stripped by reduction to Te2while Cd is stripped by oxidation to Cd2. Underpotentials are chosen so that only the top atomic layer of an element is removed. Potentials sufficient to strip the element from the bulk of the CdTe substrate are avoided. Application of the method should involve the us of a simple electrochemical cell, with solution convection. The substrate is place in the cell and a square wave applied, where each cycle results in the dissolution of a bilayer of the compound. The two potentials of the square wave correspond to underpotential stripping potentials for Cd and Te respectively. Directions for the future development of this etching method are discussed.