Formation of Thin Films of CdTe, CdSe, and CdS by Electrochemical Atomic Layer Epitaxy

Abstract

Thin films of CdTe, CdSe, and CdS have been electrodeposited by electrochemical atomic layer epitaxy (ECALE), using an automated electrochemical deposition system. Previous reports of an automated system for forming ECALE deposits involved use of a small thin layer flow cell, which revealed several drawbacks. Conversion of the thin layer cell to a thick layer design resulted in greatly improved deposit quality and reproducibility. Deposits were analyzed using electron probe microanalysis (EPMA), scanning electron microscopy (SEM), and grazing incident X-ray diffraction (XRD). The results were consistent with a layer by layer growth mode and the principles of atomic layer epitaxy. CdTe films were grown using up to 1000 ECALE cycles, and were stoichiometric through 500. The 1000 cycle films were a few percent rich in Te, under the conditions used. CdSe and CdS films formed also contained some excess chalcogenide, probably the result of less then ideal deposition parameters. Increasing amounts of particulates and surface roughening were observed for the 500 and 1000 cycle CdTe and CdSe films, relative to the 200 cycle deposits normally formed. This roughening may result from the excess chalcogenide. XRD of the films indicated cubic crystal structures with preferred (111) orientations for all three compounds.

The deposition of thin films of cadmium zinc sulfide Cd1−x Zn x S at 250 °C from spin-coated xanthato complexes: a potential route to window layers for photovoltaic cells

“…It has a lower absorbance in the UV with band gaps typically in excess of * 2.4 eV [1,[5][6][7][8]. There is also a relatively small lattice mismatches to CdS/CdTe or CIGS cells (Supporting Information; Table S6 and Figure S13) [9][10][11][12]. Such materials also establish electric fields at the heterojunction interface and may act as a buffer layer [5,12].…”

“…Numerous techniques have been used to grow CdS and Cd 1-x Zn x S thin films including dip coating [16], electrodeposition [17], chemical vapor deposition (CVD) [18], aerosol-assisted CVD (AA-CVD) [19][20][21], chemical bath deposition (CBD) [2,8,22,23], spray pyrolysis [24,25], thermal evaporation [26], successive ionic layer and reaction (SILAR) [27], thermolysis [28,29], electrochemical atomic layer epitaxy (ECALE) [11], sol-gel spin coating, [30,31] doctor's blade, [32] and others [14,21,33,34]. Spin coating (SC) is a particularly useful method for the deposition of thin films [35,36].…”

Evidence for the Diffusion of Au Atoms into the Te UPD Layer Formed on a Au(111) Substrate

“…Should this be the case, the top layer structure differentiates from that expected based on the STM and AFM observations which are typically completed within 1 h or less. Since the XRD analysis of thick deposits of CdTe by ECALE shows the formation of cubic CdTe with the ͑111͒ preferential orientation, 4 an ideally atomic layer just on the substrate is not always necessary for the formation of thick deposits using the ECALE method, in which the possible interactions with the underlying substrate become negligible. However, the interaction with the substrate becomes considerable in the formation of very thin deposits using ECALE, especially in the formation of a few atomic layers to produce some applications consisting of ultrathin layers.…”

“…[2][3][4] Since the deposition of Cd on a Au substrate easily produces intermetallic compounds, such as Cd 3 Au, 5 the first step to the formation of CdTe films by ECALE is not the reductive UPD of Cd. Rather, Te is first deposited by UPD on a Au single-crystal substrate.…”

Analysis Of The Underpotential Deposition Of Cadmium On Copper

“…Excellent reviews embracing theoretical considerations and different UPD systems are given in [1][2][3][4][5]. The systems related with cadmium attracted in the last years due to their application in the electrochemical atomic layer epitaxy (ECALE) process [6][7][8][9] and synthesis semiconductor compounds [10]. Moreover the modification of electrode surfaces through underpotential deposition enables to improve their catalytic properties, like in case a Cd-Au system [11,12].…”