NEAR-BAND-EDGE PHOTOLUMINESCENCE OF MOVPE-GROWN UNDOPED AND NITROGEN-DOPED ZNSE

Optical properties of undoped and nitrogen-doped ZnSe/GaAs epilayers g rown by MOVPE were investigated by using CW He-Cd laser excitation or by pulsed N-2-laser radiation in the temperature range between 10 and 300 K and at excitation intensities in the range of I-exc = 10(-1)-10( 6) W/cm(2). The presence of deep donor states with an ionization energ y of E-D approximate to 60 meV and acceptor states with E-A approximat e to 80 meV as well as the existence of trap levels with a concentrati on comparable to the amount of incorporated nitrogen were detected. Th e concentration of the electron-hole plasma (EHP) is saturated at I-ex c > 200 kW/cm(2) in undoped and moderately doped layers due to plasma expansion through the layer into the substrate. High doping levels as well as the presence of a barrier layer between ZnSe and the substrate leads to a further increase of the EHP concentration. The overheat of the near-surface layer which is much higher compared to the average t emperature of the irradiated area leads to a high temperature gradient (Delta T similar to 150 K) in the layer.