Spectroscopic Investigation of Strain and Acceptor Levels in Heteroepitaxial Zinc Selenide and Zinc Telluride.

Optical spectroscopic techniques, including photoluminescence (PL), reflectance, and magnetospectroscopy, are employed to study two of most important issues in wide gap heteroepitaxial II-V materials grown on III-V substrates, which are the effects of strain and lattice mismatch on the material properties, and development of effective p-type doping in ZnSe for application to blue light emitting devices. The investigation of the effects of strain on the optical properties of ZnTe on GaAs and GaSb clearly demonstrates that strain exists in ZnTe, and has important and previously unrecognized effects on the PL spectrum. A conduction band-to-acceptor transition peak has been observed and identified for the first time in the 1.7 K PL spectrum of Li-doped p-type ZnSe. Interstitial Li related features are not observed. The existence of this peak, which had been misidentified as the "R"-band must be recognized to avoid misleading efforts to improve p-type doping. The As and P related acceptor shallow levels in As and P doped ZnSe are characterized in detail for the first time. From selective pair luminescence (SPL) measurements, it is concluded that the As-acceptor shallow level is effective mass-like and the P-acceptor shallow level is apparently not in ZnSe. The splitting of the As-acceptor bound exciton as a function of magnetic field orientation suggest that the As acceptor has the point symmetry of the lattice, which suggests that it is a simple substitutional acceptor involving As on the Se site. The existence of an O-related shallow acceptor level is confirmed and the excited states of the level are determined by SPL measurements; previous reports of an O acceptor -bound exciton are however incorrect.