R. H. Mari
University of Nottingham
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Featured researches published by R. H. Mari.
Journal of Applied Physics | 2009
R. Kudrawiec; M. Syperek; P. Poloczek; J. Misiewicz; R. H. Mari; M. Shafi; M. Henini; Y. Galvão Gobato; S. V. Novikov; J. Ibáñez; M. Schmidbauer; S. I. Molina
The carrier localization phenomenon has been investigated for GaBiAs by photomodulated transmittance (PT) and photoluminescence (PL). In the case of PT measurements, a decrease in the energy-gap related PT signal has been clearly observed below 180 K. In PL spectra a broad emission band very sensitive to the excitation power has been found. In comparison to the energy-gap related transition, this band is shifted to red. The recombination time for this band at low temperature decreases from 0.7 to 0.35 ns with the increase in the emission energy. All the findings are clear evidences for strong carrier localization in this alloy.
Applied Physics Letters | 2011
D. L. Sales; Elisa Guerrero; J. F. Rodrigo; P. L. Galindo; A. Yáñez; M. Shafi; A. Khatab; R. H. Mari; M. Henini; S. V. Novikov; Matthew F. Chisholm; S. I. Molina
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.
Journal of Applied Physics | 2010
J. Ibáñez; R. Oliva; M. de la Mare; M. Schmidbauer; S. Hernández; P. Pellegrino; D. J. Scurr; R. Cusco; L. Artus; M. Shafi; R. H. Mari; M. Henini; Qiandong Zhuang; A. M. R. Godenir; A. Krier
We perform a structural and optical characterization of InAs1−xNx epilayers grown by molecular beam epitaxy on InAs substrates (x≲2.2%). High-resolution x-ray diffraction (HRXRD) is used to obtain information about the crystal quality and the strain state of the samples and to determine the N content of the films. The composition of two of the samples investigated is also obtained with time-of-flight secondary ion mass spectroscopy (ToF-SIMS) measurements. The combined analysis of the HRXRD and ToF-SIMS data suggests that the lattice parameter of InAsN might significantly deviate from Vegard’s law. Raman scattering and far-infrared reflectivity measurements have been carried out to investigate the incorporation of N into the InAsN alloy. N-related local vibrational modes are detected in the samples with higher N content. The origin of the observed features is discussed. We study the compositional dependence of the room-temperature band gap energy of the InAsN alloy. For this purpose, photoluminescence and...
Journal of Applied Physics | 2013
Mohsin Aziz; Philippe Ferrandis; Abdelmadjid Mesli; R. H. Mari; J.F. Felix; A. Sellai; Dler Jameel; Noor Al Saqri; A. Khatab; D. Taylor; M. Henini
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.
Applied Physics Letters | 2012
R. Kudrawiec; M. Latkowska; M. Welna; J. Misiewicz; M. Shafi; R. H. Mari; M. Henini; W. Walukiewicz
It has been observed that activation energies of electron traps in GaNAs layers of various nitrogen concentrations vary consistently if the N-related changes in the band structure of GaNAs and energy positions of donor levels are plotted relative to the valence band edge on the same diagram. Within this diagram, it is expected that the activation energy of electron traps of the same microscopic nature should decrease with the increase of nitrogen concentration. The identification of electron traps in GaNAs within the proposed diagram allows to interpret the broad emission at ∼0.9 eV as the donor trap–valence band and the donor acceptor pair recombination involving of these traps.
Nanoscale Research Letters | 2011
R. H. Mari; M. Shafi; Mohsin Aziz; A. Khatab; D. Taylor; M. Henini
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).
Journal of Applied Physics | 2011
M. Shafi; R. H. Mari; A. Khatab; M. Henini; A. Polimeni; M. Capizzi; M. Hopkinson
Dilute nitride GaAs1-xNx layers have been grown by molecular beam epitaxy with nitrogen concentration ranging from 0.2% to 0.8%. These samples have been studied before and after hydrogen irradiation by using standard deep level transient spectroscopy (DLTS) and high resolution Laplace DLTS techniques. The activation energy, capture cross section and density of the electron traps have been estimated and compared with results obtained in N-free as-grown and H-irradiated bulk GaAs.
Nanoscale Research Letters | 2010
M. Shafi; R. H. Mari; A. Khatab; D. Taylor; M. Henini
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.
Physica Status Solidi (c) | 2009
M. Shafi; R. H. Mari; M. Henini; D. Taylor; M. Hopkinson
Microelectronics Journal | 2009
R. Kudrawiec; P. Poloczek; J. Misiewicz; M. Shafi; J. Ibáñez; R. H. Mari; M. Henini; M. Schmidbauer; S. V. Novikov; Lyudmila Turyanska; S. I. Molina; D. L. Sales; Matthew F. Chisholm