MBE Growth and Properties of Zinc Selenide and Related Materials

Molecular beam epitaxy (MBE) has been successfully employed to grow ZnSe and related alloys on GaAs (100) substrates. High quality ZnSe films were obtained which exhibited narrow x-ray rocking curves and good surface morphologies. Controlled substitutional doping was also studied. ZnCl_2 was used as a solid source of Cl for the preparation of n-type substitutionally -doped ZnSe films. The n-type ZnSe:Cl epilayers were highly conducting and exhibited bright blue-violet luminescence at room temperature. A Hall mobility of 2480 cm ^2/V.S at 40 K was measured for an n-type ZnSe:Cl film doped to a level of ~3 times 10^{17 } cm^{-3} and for which a compensation ratio N_{ rm A}/N_{rm D} ~ 4% was calculated. This is the highest mobility ever achieved for ZnSe doped to this level. P-type ZnSe films were prepared using Li or N as the substitutional dopant. The ZnSe:Li films exhibited photoluminescence spectra at 4 K dominated by an acceptor -bound exciton peak at 2.791 eV, providing clear evidence of p-type doping. The p-type character of ZnSe:N films was identified on the basis of a donor-acceptor pair recombination peak observed in photoluminescence spectra at low temperature. ZnSe n-channel field effect transistors (FETs) grown on semi-insulating GaAs substrates have been successfully fabricated for the first time. Successful fabrication of ZnSe p-n junction light emitting diodes in which Li and Cl were used as p-type and n-type dopants, respectively, has also been achieved. These p-on-n structures emit blue light at room temperature. In addition, double heterostructures and multiquantum well structures composed of ZnSe-ZnSe_{0.9 }Te_{0.1}, ZnSe-Zn_{0.9}Cd _{0.1}Se, ZnSe-ZnS_ {0.1}Se_{0.9} and ZnS_{rm x}Se _{rm 1-x}-Zn _{rm 1-y}Cd_ {rm y}Se layers in which Li or N (p-type) and Cl (n-type) were used as dopants have been fabricated by MBE. Photoluminescence and electroluminescence spectra were studied, and photopumped stimulated emission was demonstrated for all these structures. The double -heterostructures consisting of a multiple quantum well structure of ZnS_{rm x} Se_{rm 1-x} -Zn_{rm 1-y}Cd _{rm y}Se, with n-type and p-type ZnS_{rm x}Se _{rm 1-x} cladding layers, emit bright blue electroluminescence at 2.601 eV (476 nm) at room temperature. Finally, in seeking better control of the electrical properties of multilayered structures, both conventional and modulation-doped n-type ZnSe-ZnCdSe multilayered structures were fabricated. Successful modulation-doping was confirmed by Hall effect measurements. The research which comprises this thesis is expected to impact significantly on the areas of optoelectronics (blue-green LEDs and lasers), optical communications, optical computing, and information storage using magnetic and optical recording media. In addition, the work represents important advances in materials growth and characterization of wide band gap II-VI compound semiconductors.