Novel control technique for cadmium sulfide Chemical Bath Disposition using real time monitoring of cadmium ion molarity
Cadmium sulfide Chemical-Bath-Deposition parameters are modified to allow, for the first time, real time monitoring of cadmium ion molarity using a commercially available cadmium ion Ion-Selective-Electreode at 60°C. This modification involves alterations to typical deposition parameters that eliminate the formation of cadmium hydroxide and keep cadmium ion molarity above 10-7M. The new or atypical parameters developed are pH values below 8.9 and lower moralities for all chemicals. In order to have complexation of cadmium ion driven mainly by ammonia, parameters that minimized complexation by other chemicals are found. Cadmium acetate concentration below 2mM and ammonium acetate concentration below 10mM minimize complexation. In order to keep cadmium ion molarity within the detection limits during complexation with ammonia, ammonia molarity is kept below 0.05M. For controlling proposes, decomposition of thiourea is studied with the parameter developed for monitoring of cadmium ion molarity. It is found that thiourea complexes cadmium ions, and it precipitates cadmium sulfide homogenously with cadmium ion molarities above 10-7M and pH value of 8.9. Thiourea decomposition is suppressed for pH values below 7.6, and pH values of 8.2 and 8.4 are found to suppress homogenous precipitation and favor heterogeneous deposition of cadmium sulfide with a deposition rate between 1 to 2 nm per minute. The films are considered of good quality due to a band gap very close to the ideal 2.42eV and a surface roughness of at least three smaller than of typical cadmium sulfide films.
Ordonez, Rafael, "Novel control technique for cadmium sulfide Chemical Bath Disposition using real time monitoring of cadmium ion molarity" (2010). ETD Collection for University of Texas, El Paso. AAI1559465.