Propylene sulfide as a sulfur-containing precursor in MOCVD: study of mixtures of Me2Cd and propylene sulfide in the gas, liquid and solid phases and their use in MOCVD

Abstract

Mixtures of dimethylcadmium (Me₂Cd) and propylene sulfide have been examined in the gas and liquid phases over a range of temperatures. No interaction is observed between Me₂Cd and propylene sulfide in a 1:1 molar ratio at room temperature in the gas or liquid phases, although a weak interaction is detected in the solid phase at liquid-nitrogen temperature. On heating the 1:1 mixtures of Me₂Cd and propylene sulfide to 85–250 °C, in sealed vessels, gaseous products are formed. These are principally propene and methane, in an approximately 2:1 molar ratio, while in a flow system not only are propene and methane found as the major gaseous products at 300 °C, but also a layer of solid CdS is deposited.

Using a commercial metal–organic chemical vapour deposition (MOCVD) apparatus high-quality layers of cadmium sulfide are obtained from Me₂Cd–propylene sulfide mixtures. Temperatures in the range 300–450 °C lead to growth rates in excess of 1 p µm h^–1. The unwanted pre-reaction, observed when hydrogen sulfide is used as the sulfur source in CdS deposition, is eliminated and the resulting epitaxial layers have good thickness and electrical uniformity. These experiments confirm the usefulness of propylene sulfide for the growth of CdS by MOCVD.