III-V nitrides for electronic and UV applications

AbstractTremendous progress has been made in recent years in the growth, doping and processing technologies of the wide bandgap semiconductors. The principal driving force behind this activity is the potential use of, for example, the 1114 nitrides in high-power, high-temperature, high-frequency electronic and optical devices resistant to radiation damage. This article reports the current state of the art for producing some selected devices from the III-V nitrides

Nanotechnology — growing in a shrinking world

AbstractThe ability to scale device sizes to below a micrometre, the world of nanotechnology, has led to the observation of unexpected physical phenomena and to the creation of an entirely new class of devices. Using sophisticated growth, lithographic and etching techniques it is now possible to fabricate devices with tailored band structures and, consequently, tailored electronic and optical properties. This article provides an elementary introduction to this new technology, providing a flavour of its current capabilities and future expectations

4th International Conference on Atomic Layer Epitaxy

AbstractThe 4th International Conference on Atomic Layer Epitaxy (ALE) was held at the Johannes Kepler University of Linz, Austria on the 29–31 July 1996. There were 13 countries represented at the meeting. The number of participants was around 60 from which a significant number of Japanese and Finnish. The topics discussed were III–V, SiSi Ge, surface science, oxides and growth mechanisms. The program consisted of 15 invited talks, 12 contributed papers and 21 posters. The papers will be published in Applied Surface Science. Due to space constraints, I will report only on few invited papers. A brief description is given below for those unfamiliar with ALE technique (for further details see: Vacuum, Vol. 42, Nos. 1 & 2, pp. 61–66, 1991)

Developments continue for VCSEL research

AbstractIn recent years the demand for high-performance low-cost optical interconnect components has accelerated. An ideal solution for the transmitter has been found with the development of the vertical-cavity surface-emitting laser (VCSEL). VCSELs show potential for many applications principally due to the ease of producing two-dimensional arrays. One of the most important properties of the VCSEL is its well-defined beam properties, such as circular geometry and its surface-normal emission. VCSELs have been the topic of intense research for several years now. This article will only look at some recently reported results in this field

Magnetic-field dependence of the spin states of the negatively charged exciton in GaAs quantum wells

We present high-field (<50 T) photoluminescence measurements of the binding energy of the singlet and triplet states of the negatively charged exciton in a 200-Angstrom quantum well. Comparing our data with those of other groups and with theoretical predictions we clearly show how the singlet, "bright" and "dark" triplet states may be identified according to the high-field dependence of their binding energies. We demonstrate that a very consistent behavior of the binding energy in a magnetic field has been observed in quantum wells of different widths by different groups and conclude that the triplet state found in this, as well as nearly all other experiments, is undoubtedly the bright triplet. By combining our data with that in the literature we are able to present the generic form of the binding energy of the spin states of the charged exciton in a magnetic field, which reveals the predicted singlet to dark triplet ground state transition at about 20 T

SDTC-EKF Control of an Induction Motor Based Electric Vehicle

International audienceThis paper presents the experimental implementation of sensorless direct torque control of an induction motor based electric vehicle. In this case, stator flux and rotational speed estimations are achieved using an extended Kalman filter. Experimental results on a test vehicle propelled by a 1-kW induction motor seem to indicate that the proposed scheme is a good candidate for an electric vehicle control

Fabrication of novel transparent Co3O4-TiO2 nanowires p-n heterojunction diodes for multiband photodetection applications

Axial Co3O4 - TiO2 heterojunction nanowires (NWs) were synthesized by glancing angle deposition (GLAD) technique. The p-n heterojunction showed excellent rectification ratio of 2.26 × 102 at ± 3.4 V. The forward turn on voltage of 1.5 V in the dark was reduced to 1 V under white light excitation on the device. The diode showed a maximum half-wave rectification efficiency of 7.77% at 200 Hz frequency operated with maximum ±10 V. The device showed maximum peak responsivity of 4.01 A/W and internal gain of 13.1 at 380 nm wavelength. The detectivity was calculated to be 2.82 × 1011 and 1.69 × 1011 Jones and the noise equivalent power was estimated to be 14.9 and 24.8 pW at 380 and 620 nm wavelength, respectively. The device spatial response showed sharp transition with rise and fall time of ∼0.17s and 0.21s, respectively

Experimental Control of Macroscopically Large, Schrodinger Cat like Quantum Coherent State of Bose-Einstein Condensate of Excitons as Qubits

In this work, we varied the number density of photo generated and bias driven excitons by changing the applied bias voltage and photo excitation intensity. Phase coherent periodic oscillations in photo generated capacitance as a function of the bias voltage and light intensity are measured respectively over a macroscopically large area. We then argue that presence of coherent resonant tunnelling in this well-dot heterostructure strongly restricts the available momentum space of the charge carriers within this quantum well. Consequently, the measured average electric polarization vector of the associated indirect excitons spontaneously increase below 100 K as excitonic dipoles chooses a particular phase and collectively orients along the direction of applied bias. As a result, these excitons continuously undergo Bose-Einstein condensation below a transition temperature as the density threshold is approached at regular bias intervals. Moreover, periodic presence and absence of splitting of excitonic peaks in the optical spectra based on photocapacitance confirm such tunneling induced variations in quantum coupling of electrons between quantum well and quantum dots. Observation of negative quantum capacitance due to screening of charge carriers by the quantum well indicate periodic variation of Coulomb correlations of interacting excitons with increasing bias as a precursor to condensation and vice versa. Generation of density dependent enhancement of quantum interference beats in photocapacitance oscillation with bias even under incoherent white light further confirm the presence of stable, long range spatial correlation among these indirect excitons as well as the existence excitonic matter waves. We also detected collective Rabi oscillations of these macroscopically large, multipartite, two-level, coupled and uncoupled quantum states of excitonic condensate which can be used as qubits.Comment: 43 pages, Manuscript + 11 Figure

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)