Synthesis of cadmium sulfide using the spontaneous reaction of dialkylcadmium and hydrogen sulfide

#Cadmium sulfide single crystal is used as a UV detector and in combination with other materials indium antimony (InSb) as a detector for UV and IR detectors. The final product material must meet a very strict set of specifications with respect to spectral transmission, mobility, resistivity, and detector lifetime. The single crystals are prepared using a "proprietary" process which involves chemical vapor deposition by Eagle Picher Laboratories, who is at present the single supplier. It is concluded that the characteristics of the single crystal are drastically affected by the purity of the cadmium sulfide powder used as a precursor to the single crystal. The bases for this conclusion are supported by P. D. Fochs et al, Report No. AE-1-G.1453, Clevite Corporation, Report No. FTD-TT-65-555, General Electric Company, Report No. SR-2,65gc-03 136, and Bell and Howell Research center, Technical Report AF 33-615-276.

#Because of the high priority and importance of high purity of precursor material for a single crystal product, a variety of studies have been conducted over the past twenty years with the objective of perfecting a process which would produce purer starting material for ultimate growth of single crystals with specific properties. Predominant leaders in this area include Eagle Picher Laboratories and the Clevite Corporation Research Laboratory. The synthetic work for cadmium sulfide performed by these companies involved the chemical reaction of the elements with thermal activation as necessary.

#Hydrogen sulfide is known to be acidic in solution; however, a reaction in liquid solution to yield cadmium sulfide is not desired to be pursued since the required level of purity of the finished product by this route cannot be achieved.

#FIG. 1 depicts an infrared spectra of (CH.sub.3).sub.2 Cd at 30 torr.

#FIG. 2 depicts an infrared spectra of a mixture of resulting compounds formed after the spontaneous reaction of 30 torr of (CH.sub.3).sub.2 Cd and 36 torr H.sub.2 S.

#The gas phase spontaneous reaction of a dialkylcadmium and hydrogen sulfide yields the reddish orange precipitate which is cadmium sulfide.

#Sample handling is accomplished using standard vacuum line technique. The gas phase reactions are carried out in stainless steel cells (5.times.10 cm) equipped with O-ring seals for securing windows (5 cm diameter) onto the cells. Potassium chloride windows are used on the short pathlength (5 cm) for recording the infrared spectra.

#A preferred dialkylcadmium is dimethylcadmium, and the results of the above described spontaneous reaction are summarized in the following reaction equation: