LUMINESCENCE STUDIES OF THE 1.36-EV BAND AND THE EDGE EMISSION IN MELT-GROWN GAAS-CU

Using cathodoluminescence at 80-300 K, we have measured the injection-level dependence, frequency response, and temperature dependence of the 1.36-eV band and the 1.50-eV edge emission in melt-grown GaAs : Cu. The overall luminescence is relatively weak and the 1.36-eV band is accompanied by a broad emission in the range 1-1.4 eV. We find no inherent injection-level shift in the shape or peak energy of the 1.36-eV band. With increasing temperature, the 1.36-eV band quenches out with an activation energy of 0.1 eV or greater. The frequency response of the 1.36-eV band is remarkably flat for deep-center luminescence. However, the frequency response of the edge emission is unusually slow in GaAs : Cu, particularly in samples with higher Cu concentration. Variation in injection level causes a strong variation in branching between the 1.36-eV band and the edge emission which is not explicable in terms of occupancy effects related to the relative kinetics of the two bands. It is suggested that the 1.36-eV band results from a conduction-band-to-acceptor transition whose kinetics are dominated by another process such as equilibration of a carrier trapping level in resonance with the conduction-band continuum. The same process also controls the kinetics of the edge emission transition in GaAs : Cu with high Cu concentration.