Optimization of Chemical Bath‐Deposited Cadmium Sulfide on InP Using a Novel Sulfur Pretreatment

A thiourea/ammonia pretreatment followed by chemical bath deposition of cadmium sulfide was used to passivate the surface of indium phosphide (100). The pretreatment was shown by X-ray photoelectron spectroscopy to effectively remove native oxides from the InP surface and form an indium sulfide layer. The subsequent chemical bath deposition of CdS on a sulfur-passivated surface forms a stable layer that protects the substrate from oxidation during chemical vapor deposition of SiO 2 . The passivation process was optimized for electrical response by varying the reactant concentrations of the chemical bath. Reflection high-energy electron-diffraction (RHEED) analysis showed that the pretreatment results in a (1 × 1) surface, which reconstructs to (2 × 1) after heating in vacuo to 200°C. RHEED and atomic force microscopy showed an increase in CdS surface roughness with increasing thickness corresponding to the formation of oriented surface asperities. CdS-passivated metal-insulator-semiconductor diodes exhibited a density of interface states (D it ) of 10 11 eV -1 cm -2 when calculated by the high-low method, more than one order of magnitude lower than the D it of untreated metal-insulator-semiconductor samples. A CdS layer thickness of ∼ 10 A was determined to yield optimal capacitance-voltage response for all CdS deposition conditions investigated.