Electrodeposition of Compound Semiconductors by Electrochemical Atomic Layer Epitaxy ( EC ‐ ALE )

Abstract

Abstract This chapter concerns the state of development of electrochemical atomic layer epitaxy (EC‐ALE), the electrochemical analog of atomic layer epitaxy (ALE). EC‐ALE is being developed as a methodology for the electrodeposition of compound semiconductors with nanoscale control. ALE is based on the formation of compounds, one monolayer (ML) at a time, using surface‐limited reactions. An atomic layer of one element can be electrodeposited at a potential under that needed to deposit the element on itself, and this process is referred to as underpotential deposition (UPD). EC‐ALE is the use of UPD for the surface‐limited reactions in an ALE cycle. Electrodeposition is generally performed near room temperature, avoiding problems with interdiffusion and mismatched thermal expansion coefficients. This makes EC‐ALE a good candidate to form superlattices, where the compound deposited is modulated on the nanometer scale. This chapter describes the basics of the EC‐ALE cycle, the elements that have been used to form deposits, as well as the solutions, rinsing, and potential changes. It describes the hardware presently being used by this group and other research laboratories, the compounds that have been formed, and the development of deposition cycles for various compounds. It describes the status of device formation using EC‐ALE, and goes over some of the problems and issues involved in developing cycles and growing films. Finally, given that EC‐ALE is based on surface‐limited electrochemical reactions, studies of relevant electrodeposit surface chemistry are discussed.