Electrochemical Atomic Layer Processing of Compound Semiconductors = Electrochemical Atomic Layer Processing of Compound Semiconductors

다국어 초록 (Multilingual Abstract)

We present two electrochemical methods of atomic layer processing of compound semiconductors. One is electrochemical formation of compound semiconductors, based on the principles of atomic layer epitaxy (ALE). This method is referred to ”Electrochemical Atomic Layer Epitaxy (ECALE)”. The other is electrochemical removal of atomic layers in a compound semiconductor in a sequential way. This method is called ’’Electrochemical Digital Etching (ECDE)”.
The principle of the electrochemical atomic layer processing methods is associated with a famous phenomena in electrochemistry, which is “Underpotential Deposition (UPD)”. When one element deposits on a second metal surface, the deposition occurs at a potential prior to (under) the potential of bulk deposition (i.e. deposition of the element on itself). The UPD process occurs when compound formation is favored thermodynamically. In fact, the amount of underpotentially deposited element is limited to submonolayer or full monolayer.
In the ECALE method, individual solutions of depositing elements are sequentially exposed to a substrate as in gas-phase ALE. One element is deposited on the substrate surface at an appropriate underpotential to obtain one monolayer. Then, a second element is deposited on the substrate whose surface is already covered with one monolayer of the first element. In this way, a compound semiconductor can be formed. The selection of deposition potentials is critical because one of the elements should be deposited without stripping the already-deposited atomic layers.
In the ECDE method, the top layer element of a compound semiconductor is stripped underpotentially since it has dangling bonds (i.e. the corresponding element in the bulk is more stable). Upon removing one element in the top layer, a second element, which is exposed to electrolyte, is stripped in the same way. Accordingly, layer-by-layer etching results from a sequential application of underpotentials for each elements with removing the dissolved ion.
In this seminar, experimental evidences for the electrochemical atomic layer processing will be presented. The ECALE method will be exemplified with deposition of ZnTe and CdTe on polycrystalline Au electrodes. Likewise, the ECDE method will be explained with etching of CdTe(100) surfaces. In addition, the problems associated with the methods will be discussed.