The low-temperature properties of the excitation-dependent (moving) emissions in Mg-, Be-, Cd-, and Znimplanted GaAs layers are investigated with respect to changes in temperature and excitation intensity. The substrates used were epitaxial layers, melt-grown n -type crystals, and Cr-doped semi-insulating crystals. Donor concentrations of the n -type substrates were in the range 5 X 10 13 to 2 X 10 18 electrons cm-3 • Models explaining a large energy shift are presented for both Cr-doped and n-type substrates. The moving emissions are classified into three different cases: (a) donor-acceptor-pair emission in relatively pure weakly compensated crystals; (b) donor-acceptor-pair emission in impure strongly compensated crystals; and (c) a radiation transition from the conduction-band tails to the valence band. The donoracceptor-pair emission in tile impure compensated crystals shows the shift to lower energy with an increase of temperature in the temperature range 4-50'K, while the donor-acceptor-pair emission in pure crystals behaves in the usual manner. This is due to the increase in the random impurity potential. The large shift of emission peaks originates in the impure compensated regions, i.e., the near-surface region due to the out-diffusion of the implanted atoms in Cr-doped substrates, and the highly resistive layer between the pand n -type region in n -type substrates. Additional compensating donors are found to be defect-type donors, As vacancies. The formation of As vacancies differs depending on the substrate materials. The role of the As vacancy in forming a compensated region is discussed.
Acceptors present in undoped p-type conducting GaAs have been studied with photoluminescence, temperature-dependent Hall measurements, deep level transient spectroscopy, and spark source mass spectrometry. It is shown that p-type conduction is due to presence of the shallow acceptor CAs and the cation antisite double acceptor GaAs. The first and second ionization energies determined for GaAs are 77 and 230 meV from the valence-band edge.
We report the excitation intensity dependent photoluminescence properties of GaAs1−xSbx layers grown by molecular beam epitaxy on InP substrates. Photoluminescence consists of the bound exciton and the quasi-donor-acceptor pair transitions for the layers in the range of 0.26≤x≤0.94. The concentration modulation produced by the relaxation of the misfit strain between the epitaxial GaAs1−xSbx layer and InP substrate is responsible for the quasi-donor-acceptor pair transition. A large Stokes shift between the photoluminescence transition of the bound exciton and the band gap determined by the optical absorption measurements is also consistent with our model of concentration modulation.
InGaN/GaN multiple quantum wells (MQWs) grown with various growth interruptions between the InxGa1−xN well and GaN barrier by metalorganic chemical vapor deposition were investigated using photoluminescence (PL), high-resolution transmission electron microscopy, and energy filtered transmission electron microscopy (EFTEM). The integrated PL intensity of the MQWs with growth interruptions is abruptly reduced compared to that of the MQW without growth interruption. Also, as the interruption time increases the peak emission shows a continuous blueshift. Evidence of indium clustering is directly observed both by using an indium ratio map of the MQWs and from indium composition measurements along an InGaN well using EFTEM. The higher-intensity and lower-energy emission of light from the MQW grown without interruption showing indium clustering is believed to be caused by the recombination of excitons localized in indium clustering regions and the increased indium composition in these recombination centers.
The behavior of the low-temperature emission spectra of melt-grown p-type and Cd-implanted n-type CuInSe2 with changes in temperature and excitation intensity have been investigated. Broad-band emission was dominant in the melt-grown crystals grown under an excess Se atmosphere. Generally, the broad-band peak was observed to occur at ∼0.94–0.95 eV, all peaks lying in the broad range of energy of ∼0.87–0.95 eV at 4.2 °K. The band was observed to shift to higher energy as the excitation intensity or temperature was increased, which implies that the band is due to a donor-acceptor pair mechanism. The spectral characteristics are explained by the presence of an acceptor level (EA=85±2 meV) and a donor level (ED=65±2 meV) and by compensation-dependent band shift in the p-type crystals. Acceptors and donors responsible for the pair band appear to be Cu and Se vacancies. The change in the peak energy of the band per decade of excitation intensity was found to be in the range 4–25 meV at 4.2 °K. The shift of the broad-band peak to lower energies and the increase in the magnitude of the energy shift due to the excitation intensity are consistent with high doping and compensation. A broad emission band was also observed in Cd-implanted crystals at low temperatures. The temperature dependence of the broad band in these crystals was opposite to that of the p-type crystals, the peak shifting to lower energy with an increase in temperature.
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