We report on photoluminescence and photoluminescence excitation experiments performed on hexagonal GaN layers grown on a Sapphire substrate. Information about extrinsic and intrinsic optical properties have been obtained. We show that, at low temperature, the fundamental A excitons are preferentially involved in the relaxation towards the neutral donor bound exciton photoluminescence line, while electron-hole pairs rather participate in the relaxation towards D0−A0 emission and the yellow band. The relaxation from the A exciton towards the yellow band and D0−A0 emission is made easier by temperature. The band structure of the GaN layers has been determined from temperature dependent photoluminescence excitation spectroscopy: A and C excitons and A continuum band gap have been identified up to 210K.
AbstractEfficient, low-temperature luminescence at energies far above that of the exciting cw-laser is reported at junctions of GaAs-GaInP2 and GaAs-AlxGa1−x.InP2. The signal originates from the high-band gap layers and disappears only if the excitation energy is tuned below the GaAs band gap, as monitored by up-converted photoluminescence excitation spectroscopy. This shows that the non-linear process is induced by the generation of electrons and holes in the GaAs. Furthermore, it is found that the up-conversion is only observed if the (A1)GaInP2 layers are CuPtB long-range ordered. The reason for this is the inherent presence of metastable states in these ordered alloys. It is argued that cold Auger processes cause the nonlinear effect at these type I interfaces.
The irradiation-induced effects in Cu(In,Ca)Se2 thin films after irradiation with hydrogen ions with dose of [Formula: see text][Formula: see text]cm[Formula: see text] and different energies in the range of 2.5–10[Formula: see text]keV were studied. Irradiated and nonirradiated thin films were investigated by low-temperature (4.2[Formula: see text]K) photoluminescence and photoluminescence excitation methods. The appearance of intense bands at [Formula: see text][Formula: see text]eV and 0.77[Formula: see text]eV in the photoluminescence spectra may be related to radiative recombination on the irradiation-induced defects with deep energy levels in the bandgap of Cu(In,Ca)Se2 solid solutions. A possible nature of these defects and process of radiative recombination are discussed.
AbstractResidual stress in MOVPE grown GaAs on (100)Si substrates is investigated using Haman spectroscopy, X-ray diffraction, low temperature photoluminescence and photoluminescence excitation spectroscopy experiments. At room temperature, 2 µm-thick GaAs/Si is found to be under biaxial (100) tensile stress of X = 1.8 ± 0.3 kbar, near the epilayer surface. The stress magnitude decreases as the distance from interface decreases. PL and PLE studies on post-growth thermally annealed GaAs/Si reveal coexistence of unstrained and strained GaAs.
ABSTRACTThin-film Zn2GeO4:Mn phosphors with lower temperature of crystallization and potentially compatible with industrial technologies were investigated. The technology of thin films synthesis has been developed and their structure and crystal parameters have been investigated. Photoluminescence excitation spectra, photoconductivity, temperature dependencies and ESR-spectra of manganese ions were studied. A mechanism for luminescence in this phosphor has been proposed. Results are presented of cathodo- and electro-luminescence of thin film structures of Zn2GeO4:Mn.
Photoluminescence excitation spectroscopy of GaN thin layers as a function of temperature