A. Khatab

Distribution of bismuth atoms in epitaxial GaAsBi

The distribution of Bi atoms in epitaxial GaAs(1−x)Bix is analyzed through aberration-corrected Z-contrast images. The relation between the atomic number and the intensity of the images allows quantifying the distribution of Bi atoms in this material. A bidimensional map of Bi atoms is extracted showing areas where nanoclustering is possible and evidencing the location of Bi at As-substitutional positions in the lattice. The distribution of Bi atoms differs from a random spatial pattern of Bi atoms in the material.

Deep-level transient spectroscopy of interfacial states in “buffer-free” p-i-n GaSb/GaAs devices

A systematic study was carried out on defect states in Interfacial Misfit (IMF) unpassivated and Te-passivated IMF in p-i-n GaSb/GaAs devices using Deep Level Transient Spectroscopy (DLTS) and Laplace DLTS. Additionally, Current-Voltage (I–V) measurements were performed, which showed that the turn-on voltage (Von) of passivated samples is lower than that for unpassivated samples; an effect which can be explained by the introduction of new defects states near to the interface of GaSb/GaAs, where Te was incorporated to passivate the IMF. The Capacitance-Voltage (C-V) analysis demonstrates that these new states are the consequence of adding Te at the misfit of GaSb/GaAs. Furthermore, DLTS measurements reveal a distribution of states including a main midgap energy level, namely the well documented EL2 trap, with some peculiar behaviour. Most of these levels are related to interface states that are generated by the mismatch between GaAs and GaSb. Originally, the addition of Te atoms was thought to passivate these interface states. On the contrary, this paper, which attempts at correlating the current-voltage and capacitance-voltage characteristics to the DLTS results, shows clearly that Te atoms increase the density of interface states.

Strain and localization effects in InGaAs(N) quantum wells: Tuning the magnetic response

We investigated effects of localization and strain on the optical and magneto-optical properties of diluted nitrogen III–V quantum wells theoretically and experimentally. High-resolution x-ray diffraction, photoluminescence (PL), and magneto-PL measurements under high magnetic fields up to 15 T were performed at low temperatures. Bir-Pikus Hamiltonian formalism was used to study the influence of strain, confinement, and localization effects. The circularly polarized magneto-PL was interpreted considering localization aspects in the valence band ground state. An anomalous behavior of the electron-hole pair magnetic shift was observed at low magnetic fields, ascribed to the increase in the exciton reduced mass due to the negative effective mass of the valence band ground state.

Electrical characterisation of deep level defects in Be-doped AlGaAs grown on (100) and (311)A GaAs substrates by MBE

The growth of high mobility two-dimensional hole gases (2DHGs) using GaAs-GaAlAs heterostructures has been the subject of many investigations. However, despite many efforts hole mobilities in Be-doped structures grown on (100) GaAs substrate remained considerably lower than those obtained by growing on (311)A oriented surface using silicon as p-type dopant. In this study we will report on the properties of hole traps in a set of p-type Be-doped Al0.29Ga0.71As samples grown by molecular beam epitaxy on (100) and (311)A GaAs substrates using deep level transient spectroscopy (DLTS) technique. In addition, the effect of the level of Be-doping concentration on the hole deep traps is investigated. It was observed that with increasing the Be-doping concentration from 1 × 1016 to 1 × 1017 cm-3 the number of detected electrically active defects decreases for samples grown on (311)A substrate, whereas, it increases for (100) orientated samples. The DLTS measurements also reveal that the activation energies of traps detected in (311)A are lower than those in (100). From these findings it is expected that mobilities of 2DHGs in Be-doped GaAs-GaAlAs devices grown on (311)A should be higher than those on (100).

Deep-level Transient Spectroscopy of GaAs/AlGaAs Multi-Quantum Wells Grown on (100) and (311)B GaAs Substrates

Si-doped GaAs/AlGaAs multi-quantum wells structures grown by molecular beam epitaxy on (100) and (311)B GaAs substrates have been studied by using conventional deep-level transient spectroscopy (DLTS) and high-resolution Laplace DLTS techniques. One dominant electron-emitting level is observed in the quantum wells structure grown on (100) plane whose activation energy varies from 0.47 to 1.3 eV as junction electric field varies from zero field (edge of the depletion region) to 4.7 × 106 V/m. Two defect states with activation energies of 0.24 and 0.80 eV are detected in the structures grown on (311)B plane. The Ec-0.24 eV trap shows that its capture cross-section is strongly temperature dependent, whilst the other two traps show no such dependence. The value of the capture barrier energy of the trap at Ec-0.24 eV is 0.39 eV.

Absorption and photoluminescence spectroscopy of Er3+-doped SrAl2O4 ceramic phosphors

A spectroscopic characterization of Er3+-doped SrAl2O4 phosphor materials synthesized by a solid-state reaction method with Er concentrations varying from 0.1 to 1 mol% has been performed by studying photoluminescence (PL) in the temperature range 10 to 360 K and absorption spectra. PL signals containing five emission bands at 1492, 1529, 1541, 1558, and 1600 nm, respectively, have been observed at room temperature for Er3+ transitions in the near infrared region. The samples exhibit a main luminescence peak at 1.54 µm, which is assigned to recombination via an intra-4f Er3+ transition. Sharp bands centered at around 378, 488, 521, 651, 980, 1492, and 1538 nm in the absorption spectra can be associated with transitions from 4I15/2 level to 2H9/2, 4F7/2, 2H11/2, 4F9/2, 4I11/2, 2H11/2, and 4I13/2 levels, respectively. The sharp emission peaks and excellent luminescence properties show that SrAl2O4 is a suitable host for rare-earth-doped phosphors, which may be suitable for optical applications.