Low Pressure Vapor Phase Growth and Control of Electrical and Optical Properties of Zinc Selenide Single Crystalline Thin Films

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Single crystalline thin films of zinc selenide (ZnSe) have been grown on GaAs substrates by using low pressure vapor phase epitaxy (LPVPE) technique, in which zinc and selenium vapors are supplied into hydrogen atmosphere with pressure of 10^<-6>-10^<-1> Torr. A high reproducibility in growth experiment was attained by utlizing the hydrogen RF plasma cleaning of substrate surface just before the epitaxial growth. The VI/II ratio during the growth was precisely controlled and high-purity undoped ZnSe layers, which exhibit low-temperature photoluminescence spectra dominated by the free exciton emission, were grown.Undoped ZnSe layers grown at 0.1 Torr were of high resistivities. The carrier concentration was increased by In doping and controlled in the range of 10^<16>-10^<18> cm^<-3>. When the growth pressure was 10^<-4> Torr, undoped layers showed low resistivities of several .cm. The growth pressure dependence of the layer resistivity indicates that the density of deep levels compensating the residual shallow donors varies with the growth pressure. An 2n-doped layer with room-temperature carrier concentration of 5x10^<15> cm^<-3> had a low-temperature electron mobility higher than 800 cm^2/v.sec. The high mobility indicates low densities of residual impurities. When NH_3 gas was introduced into the growth chamber, a new emission line due to recombination of excition bound to a shallow acceptor was observed at 2.793 eV, and the emission increased in intensity as the concentration of NH_3 was increased. The acceptor bound exciton emission intersity decreased with increasing the VI/II ratio, which ascertained that the emission was due to N acceptor at Se site.