Electrodeposition of compound semiconductors on indium phosphide (INP) using Electrochemical Atomic Layer Epitaxy (EC-ALE)
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Gold or metals (Ag, Cu, Pt) have been used as substrates for electrodeposition of compound semiconductors, or atleast with Electrochemical Atomic Layer Epitaxy (EC-ALE) method. EC-ALE is a layer-by-layer deposition technique with atomic level control at each layer. Indium phosphide (InP), a III-V compound semiconductor, was examined as a substrate for EC-ALE process. A n-type, single crystal InP(100) wafer was considered for the study. All the work was performed in an ultrahigh vacuum – electrochemistry (UHV-EC) system with the help of sensitive surface techniques such as Auger electron spectroscopy (AES) and low energy electron diffraction (LEED). InP(100) was treated with Br2/CH3OH solution, HF etch, UV-ozone oxidation, and ion bombardment and annealing to clean the surface from carbon and oxygen contaminations. Contaminant free surface referred to as ‘clean’ InP(100) with (2X4) reconstructed surface, was attained after ion bombardment and annealing treatment. Electrochemical etching of ‘clean’ InP revealed nanoclusters of metallic In on the surface. Oxidation of metallic In was achieved in 10 mM HCl at -0.6 V to form ‘stable’ InP(100) with (1X1) structure. Electrochemistry of Te in 0.1 mM TeO2, 1 mM Na2B4O7 (pH 9) solution displayed irreversible bulk Te deposition and no Te underpotential deposition (UPD). Atomic layer of Te was obtained by reducing excess Te, from bulk deposition, to soluble telluride in 1 mM K2SO4, 1 mM Na2B4O7 (pH 9) solution at -0.98 V. Cd was only deposited as bulk Cd with nucleation and growth on both ‘clean’ and ‘stable’ InP(100). Whereas, on a Te modified InP surface UPD Cd was found at -0.43 V in 0.2 mM CdSO4, 10 mM K2SO4, 0.4 mM CH3COONa and 0.4 mM CH3COOH (pH 4.7) solution. EC-ALE cycle for electrodeposition of CdTe: deposit bulk Te on ‘stable’ InP(100) at -0.8 V in Te solution, then reduce excess Te to telluride at -0.9 V in blank solution and finally, deposit UPD Cd at -0.58 V in Cd solution. AES after three cycles of deposition proved CdTe was growing in a layer-by-layer manner. Similarly, Sb2Te3 was also grown using EC-ALE with 0.1 mM SbCl3, 0.1 M HCl (pH 1.69) solution and UPD Sb was found at -0.26 V.