Electrochemical Atomic Layer Processing

Abstract

Atomic layer processing with electrochemical control is discussed. A method for the electrodeposition of compound semiconductors based on the principles of atomic layer epitaxy (ALE) is reported, with specific reference to the formation of ZnTe. This method is referred to as electrochemical atomic layer epitaxy (ECALE). A number of II-VI compounds have been formed using this method, including: CdTe, CdSe, CdS, ZnTe, ZnSe, ZnS and HgSe. Initial studies of GaAs and PbSe have also been pursued. A computer-controlled electrochemical flow deposition system is described. The system has been constructed to form thin-films of the compounds listed above using the ECALE methodology. In addition, an analogous digital electrochemical etching procedure has been developed, and used to etch CdTe substrates. The etching cycle consists of oxidizing off the top atomic layer of Cd atoms at a relatively positive potential, followed by reducing off the top layer of Te atoms at a relatively negative potential. Atomic Force Microscopy (AFM) has been used to image the resulting features. ECALE and the digital electrochemical etching process are both based on selecting potentials where an atomic layer of an element is deposited, or removed, in a surface limited reaction. The potentials used are referred to as underpotentials in the electrochemical literature. The atomic layer deposition process is referred to as underpotential deposition (UPD).