STRUCTURAL AND OPTICAL CHARACTERIZATION OF ZNSE SINGLE-CRYSTALS GROWNBY SOLID-PHASE RECRYSTALLIZATION

We investigate by high-resolution x-ray diffraction (HRXRD), temperatu re-dependent photoluminescence (PL) and reflectivity spectroscopies, a nd low-temperature selective-photoluminescence spectroscopy ZnSe singl e crystals grown by solid-phase recrystallization. HRXRD reveals the h igh structural perfection of the samples which exhibit rocking-curve l inewidths in the 15-20 arcsec range. The low-temperature PL spectra ar e dominated by the so-called I-1(deep) excitonic line, a neutral-accep tor bound-exciton line I-1, the free-exciton emission FX, and the n=2 excited state of FX. We identify the main residual impurities to be Li accepters. Donor-acceptor pair bands are very hardly detected at low temperature which indicates a low donor content. A major characteristi cs of these samples is the quasi-absence of any Cu-related deep emissi on which generally plagues the PL spectra of bulk ZnSe. Consequently, I-1(deep) is ascribed to Zn-vacancy-donor complexes. Finally, from the temperature dependence of the PL emission and reflectivity, the band- gap energy of bulk ZnSe is found to linearly shrink with the temperatu re above 80 K at a rate of -4.3X10(-4) eV K-1. The room-temperature ga p is estimated to 2720+/-2 meV. Our results indicate that solid-phase recrystallization produces ZnSe samples with the highest structural qu ality and purity achievable at present time. (C) 1996 American Institu te of Physics.