Optimization of chemical bath-deposited cadmium sulfide on InP using a novel sulfur pretreatment

A thiourea/ammonia pretreatment followed by chemical bath deposition of cad mium sulfide was used to passivate the surface of indium phosphide (100). T he pretreatment was shown by X-ray photoelectron spectroscopy to effectivel y remove native oxides from the InP surface and form an indium sulfide laye r. The subsequent chemical bath deposition of CdS on a sulfur-passivated su rface forms a stable layer that protects the substrate from oxidation durin g chemical vapor deposition of SiO2. The passivation process was optimized for electrical response by varying the reactant concentrations of the chemi cal bath. Reflection high-energy electron-diffraction (RHEED) analysis show ed that the pretreatment results in a (1 x 1) surface, which reconstructs t o (2 x 1) after heating in vacuo to 200 degrees C. RHEED and atomic force m icroscopy showed an increase in CdS surface roughness with increasing thick ness corresponding to the formation of oriented surface asperities. CdS-pas sivated metal-insulator-semiconductor diodes exhibited a density of interfa ce states (D-it) of 10(11) eV(-1) cm(-2) when calculated by the high-low me thod, more than one order of magnitude lower than the D-it of untreated met al-insulator-semiconductor samples. A CdS layer thickness of similar to 10 Angstrom was determined to yield optimal capacitance-voltage response for a ll CdS deposition conditions investigated. (C) 1999 The Electrochemical Soc iety. S0013-4651(98)04-023-3. All rights reserved.