Organometallic Vapor Phase Epitaxy of Zinc Selenide: Growth and Doping Studies.

ZnSe at present is the most promising material for the commercial fabrication of blue light emitting devices. The successful fabrication and performance of these blue light emitting devices depends primarily on the structural, optical and electrical properties of the materials used to fabricate them. This study involves the epitaxial growth of ZnSe by organometallic vapor phase epitaxy (OMVPE) and the structural, optical and electrical characterization of undoped and doped ZnSe. The growth of ZnSe was studied over a temperature range of 300^circC-575 ^circC. Very low growth rates were obtained for temperatures below 450^circ C using conventional OMVPE growth techniques. Photo -assisted OMVPE enabled low temperature growth between 300 ^circC-400^ circC. These layers were seen to exhibit superior structural and optical properties over those grown at higher temperatures. P-type doping studies were undertaken using arsine for arsenic doping of ZnSe and a novel precursor, phenylhydrazine (PhHz) for nitrogen doping of ZnSe. Arsenic doped layers did not exhibit p-type characteristics under conventional or photo-assisted growth techniques. Flow modulation growth techniques were also explored. A number of flow profiles of DMZn, DMSe and AsH_3 were used. The use of Cd-As adduct doping was also attempted. All layers were found to be semi-insulating, and As was seen to incorporate as a deep level impurity in ZnSe. Nitrogen (N) doped layers exhibited p-type characteristics only under low temperature photo-assisted growth. These layers were seen to contain N concentrations of more than 5 times 10^{18 } cm^{-3}. A net carrier concentration (N_{rm A}-N_{rm D}) of about 1 to 2 times 10 ^{15} cm^ {-3}, was obtained for layers with a net N concentration of 2.5 times 10 ^{18}/cm^3, using extremely low dopant partial pressures of 10 ^{-8} atm. The partial pressure ratio of PhHz/DMSe ~ 1 times 10^{-4} was used, demonstrating the effectiveness of the new dopant source. Low temperature growth kinetics with the above dopant source were also investigated. The effect of growth temperature and the PhHz flow rate on the growth rate is reported. A possible model for the incorporation of nitrogen is presented.