Structural and optical characterization of ZnSe single crystals grown by solid-phase recrystallization

We investigate by high-resolution x-ray diffraction (HRXRD), temperature-dependent photoluminescence (PL) and reflectivity spectroscopies, and low-temperature selective-photoluminescence spectroscopy ZnSe single crystals grown by solid-phase recrystallization. HRXRD reveals the high structural perfection of the samples which exhibit rocking-curve linewidths in the 15-20 arcsec range. The low-temperature PL spectra are dominated by the so-called I-1(deep) excitonic line, a neutral-acceptor 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 characteristics of these samples is the quasi-absence of any Cu-related deep emission 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 temperature above 80 K at a rate of -4.3X10(-4) eV K-1. The room-temperature gap is estimated to 2720+/-2 meV. Our results indicate that solid-phase recrystallization produces ZnSe samples with the highest structural quality and purity achievable at present time. (C) 1996 American Institute of Physics.