Near-band-edge photoluminescence of MOVPE-grown undoped and nitrogen-doped ZnSe

Abstract

Optical properties of undoped and nitrogen-doped ZnSe GaAs epilayers grown 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 energy of E D ≈ 60 meV and acceptor states with E A ≈ 80 meV as well as the existence of trap levels with a concentration comparable to the amount of incorporated nitrogen were detected. The concentration of the electron-hole plasma (EHP) is saturated at I exc > 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 temperature of the irradiated area leads to a high temperature gradient ( ΔT ∼ 150 K) in the layer.