The application of PbTe as a molecular tellurium source in the growth of n-type GaAs:Te by molecular beam epitaxy (MBE) has been investigated. We obtained free-carrier concentrations ranging from 2×1016 to 2×1019 cm−3. In particular in degenerate n-type material, excellent 77 K Hall mobilities were achieved. Even at high impurity concentrations (≳1018 cm−3), Te was not found to accumulate at the surface if a true Pb-saturated (n-type) starting material was used as dopant source. Using low-temperature photoluminescence measurements, we further studied the influence of the doping concentration on the shift of the Fermi level and on the radiative recombination across the fundamental gap in heavily n-doped GaAs:Te. Calculations based on the Burstein-Moss shift and on the band tailing effect, as well as a line shape analysis, were performed for a distinct interpretation of the observed luminescence behavior. At concentrations below 5×1017 electrons cm−3, band-acceptor transitions involving residual carbon acceptors act as dominant recombination process. Above 1018 electrons cm−3, however, the luminescence spectra can be well described by indirect transitions between free electrons in the conduction band and localized acceptor-like centers in the deeper tail states above the valence band edge.

No abstract

Mass-separated 56Fe+ ions were implanted into Si(100) at 350 °C using three different energies and doses of 140 keV (1.32×1017 cm−2), 80 keV (6.20×1016 cm−2), and 50 keV (3.56×1016 cm−2). Their optical properties were investigated as a function of subsequent annealing temperature and its duration time. X-ray diffraction analysis revealed that polycrystalline semiconducting β-FeSi2 layers are formed in the as-implanted and annealed samples. From Rutherford backscattering spectrometry analysis, the formation of β-FeSi2 up to the surface was confirmed, and the average thickness and composition of the layers at peak concentration were estimated to be 70–75 nm and Fe:Si=1:2.0–2.2, respectively. The types of optical transition and the inverse logarithmic slope (E0) of the Urbach tail were investigated using room temperature optical absorption measurements. All the synthesized β-FeSi2 layers exhibited a direct transition with direct band-gap energies (Egdir) of 0.802–0.869 eV and with high optical absorption coefficients extending to 105 cm−1 at photon energy above 1.0 eV. The E0 value characteristic of the Urbach tail was observed to decrease from 260 to 100 meV with elevating annealing temperature. Some of the materials having E0<160 meV showed two strong photoluminescence (PL) emissions peaked at 0.805–0.807 eV (No. 1) and 0.840–0.843 eV (No. 2) at 2 K, whereas those with E0≳250 meV exhibited only weak emissions. From the results of the temperature- and excitation power-dependent PL measurements, emissions Nos. 1 and 2 were attributed to the trap-related recombinations related to β-FeSi2, with thermal activation (quenching) energies of 54.7 and 46.7 meV, respectively.

No abstract

Optical properties of CuInSe2 (CIS) films grown on (001) GaAs by molecular beam epitaxy (MBE) have been investigated by means of low temperature photoluminescence (PL) spectroscopy. Distinct emission lines including a bandedge emission were observed reproducibly from Cu-rich films, indicating high crystalline quality. Such well-defined PL spectra have made possible the extensive characterization of radiative recombination processes through the intrinsic defects in this material; some of the emission lines were attributed to phonon replicas with a phonon energy of 28–29 meV for the first time. PL spectra were found to be very sensitive to the MBE growth parameters such as substrate temperature, suggesting dominant defects in CIS epitaxial films can be controlled by varying the growth conditions.