Optical characterization of long -term ordered and nanocrystalline GaP

Abstract

The paper generalizes some results of the United States/Moldova program on advanced composite organic and semiconductor light emitters. High density exciton system bound to N impurity superlattice grown by modern technologies and GaP:N, GaP:N:Sm nanocrystals distributed in transparent fluorine-containing polymers will be used as the base elements for new generation of optoelectronic devices. The work seeks to expand further the applications of GaP itself through the formation of nanocomposites. Classic and new methods are applied for preparation of GaP:N nanoparticles with the controlled dimensions developed clear quantum confinement effect. The long-term ordered bulk GaP crystals as well as their nanoparticles have been investigated by TEM, XRD, Raman scattering, and luminescent methods. The evolution of the Raman Light Scattering and luminescence spectra is reported from pure and doped GaP single crystals grown over 40 years ago and evaluated approximately every 15 years. For the first time bright luminescence of the nanoparticles and “hot” luminescence of the ordered crystals due to their high perfection and low level of nonradiative recombination are detected at room temperature in the wide spectral region at the photon energies considerably more than the indirect forbidden gap compared with bulk just prepared crystals where the luminescence is absent at room temperature and limited by the edge of the indirect forbidden band at low temperatures. Independently on temperature the unique ordered GaP:N:Sm system generates with high efficiency luminescence of the N recombination centers uniformly intermixed with Sm activators. Our results clearly indicate the long-term impurity ordering and formation of a new type of crystal lattice where periodically disposed impurities located instead of host P atoms or in interstitials modify, improve and essentially change luminescent characteristics. To the best of our knowledge, this is the longest running set of experiments on a single set of samples to study the temporal effects of crystal lattice and impurity ordering.