Growth of Epitaxial Zinc Sulfide, Zinc Selenide, and Zinc SELENIUM(1-X) Sulfur(x) Alloy Thin Films, Multilayers and Superlattices by Pulsed-Laser Ablation.

Pulsed KrF (248nm) laser ablation of ZnS and ZnSe targets was used to grow high quality ZnS and ZnSe thin films on GaAs(001), GaAs(111) and GaP(001) substrates. For both ZnS and ZnSe, true three-dimensional epitaxial growth was realized on GaAs(001). For films grown on GaAs(111), two types of domains were observed with respect to the underlying GaAs substrate. Stacking faults were the dominant defects present in the ZnS films. The upper bound for the stacking fault density was rho_ {rm sf} ~ 2.5 times 10^ {10} cm-cm^{-3}. Misfit dislocations were found to be the dominant defects present in the ZnSe films. For a 225 nm thick ZnSe film, the misfit dislocation density was rho_{rm d} = 1.6 times 10^{14} cm^{ -3}.. Dielectric function measurements of the ZnS and ZnSe films on GaAs(001) showed that the films are of high optical quality and that the bandstructure is maintained. Photoluminescence measurements of these films showed donor- and acceptor -bound excitonic emissions. Both films also showed emission from the free exciton. Strained layer superlattices of the form (ZnSe) _{rm m}-(ZnS) _{rm n} were grown. The x-ray diffraction pattern from a sample having 65 periods of compositional modulation showed several orders of superlattice satellite peaks; the separation of these peaks corresponded a modulation period of L = 4.8 nm. This compared well (only 4% difference) with the desired value. A new technique that utilized ablation of ZnSe into a low-pressure H_2S gas ambient was developed to permit fabrication of rm ZnSe_{1-x}S_{x} alloy films. To evaluate this spatial control over film composition, a rm ZnSe_{1-x}S _{x} multilayered epitaxial structure was fabricated which simultaneously incorporated both continuously graded and successive abrupt, periodic compositional changes. This same technique also was applied to incorporate doping elements into ZnS films. The processes involved in the growth of ZnS, ZnSe and rm ZnSe_{1-x}S _{x} alloy films also were investigated.