CATHODOLUMINESCENCE OF ZNSE(BI)AL CRYSTALS

The cathodoluminescence (CL) in ZnSe crystals annealed at T=1200 K in a Bi melt containing an aluminum impurity is investigated. The spectra are recorded for different excitation levels, temperatures, and detec tion delay times t(0). As t(0) is increased, the intensity of the oran ge band at lambda(max)=630 nm (1.968 eV) in the CL spectrum decreases in comparison to the intensity of the dominant yellow-green band at la mbda(max)=550 nm (2.254 eV), whose half-width increases in the tempera ture range 6-120 K and then decreases as the temperature increases fur ther. It is shown that such behavior of the yellow-green band is cause d by the competition between two processes: recombination of donor-acc eptor pairs and of free electrons with holes trapped on accepters. The former mechanism is dominant at low temperatures, and the latter mech anism is dominant at high temperatures. At T similar to 120 mK the con tributions of the two mechanisms to the luminescence are comparable. T he resultant structureless band then achieves its greatest half-width, which is dictated by the interaction of the recombining charge carrie rs with longitudinal-optical and longitudinal-acoustic phonons and wit h the free-electron plasma. The mean number of longitudinal-optical ph onons emitted per photon is determined mainly by their interaction wit h holes trapped on deep accepters in the form of Al atoms replacing Se . The donor in the pair under consideration is an interstitial Al atom . (C) 1997 American Institute of Physics.