Electrical activation studies of Si-implanted AlGa1-xN (x = 0.1 and 0.18) grown on sapphire substrate have been made as a function of anneal time, anneal temperature, and ion dose. Silicon implantation was done at room temperature with a dose ranging from 5 x 10(13) to 5 x 10(15) cm(-2) at 200 keV. The samples were proximity cap annealed from 1100 to 1250 degrees C for 5-40 min with a 500 angstrom-thick AlN cap in a nitrogen environment. The electrical activation efficiencies of 84% and 75% were obtained for the Al0.1Ga0.9N after annealing at 1200 degrees C for 40 min for a dose of 5 x 10(13) and 1 x 10(14) cm, respectively. For the Al0.18Ga0.82N, nearly 100% activation for a dose of 5 x 10(14) cm(-2) and 94% for a dose of 1 x 10(15) cm(-2) were achieved after annealing at 1250 degrees C and 1200 degrees C for 20 min, respectively. Both the activation efficiency and mobility increase with anneal time and anneal temperature, indicating an improved implantation damage recovery. The highest mobility obtained at room temperature is 89 cm/Vs for the Al0.1Ga0.9N samples having doses of 5 x 10(13) and 1 x 10(14) cm(-2) and annealed at either 1200 degrees C for 40 min or 1250 degrees C for 20 min. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

We report on the fabrication of UV light-emitting diodes (LEDs) based on a p – n junction n -ZnMgO/ n -ZnO/ p -AlGaN/ p -GaN semiconductor triple-heterostructure. Radio-frequency plasma-assisted molecular beam epitaxy was used to grow the complete heterostructure on p -AlGaN/ p -GaN c -plane sapphire templates. Cross-sectional transmission electron microscopy showed single-crystal quality of the pseudomorphically grown ZnO active region of the device. The LEDs were fabricated by a process involving both wet and dry etching. Electroluminescence emission most likely associated with ZnO excitonic transition was observed up to 370°C. The results show the potential of ZnO-based materials for UV emitters of potentially lower cost and with comparable or higher emission intensity than comparable AlGaN/GaN devices.

Electrical and magnetic properties, room temperature optical absorption bands, and 300 and 90K microcathodo luminescence (MCL) bands were studied in heavily Mn and Co doped (1–5at.%) bulk ZnO crystals. Optical absorption bands near 1.9eV (Co) and 2eV (Mn) and MCL bands near 1.84eV (Co) and 1.89eV (Mn) are found to be associated with transition metal (TM) ions. These bands are assigned to internal transitions between the levels of the substitutional TM ions. The temperature dependence of the resistivity of the ZnO showed activation energies of ∼35meV in all cases and the electron mobilities were decreased relative to the undoped material.

ZnO films grown by pulsed-laser deposition on c-plane Al2O3 substrates were annealed at temperatures up to 600 °C to produce n-type carrier concentrations in the range 7.5×1015–1.5×1020 cm−3. After high-dose (3×1016 cm−2) Mn implantation and subsequent annealing at 600 °C, all the films show n-type carrier concentrations in the range 2–5×1020 cm−3 and room temperature hysteresis in magnetization loops. The saturation magnetization and coercivity of the implanted single-phase films were both strong functions of the initial anneal temperature, suggesting that carrier concentration alone cannot account for the magnetic properties of ZnO:Mn, and that factors such as crystalline quality and residual defects play a role.

A review of recent results on transition metal doping of electronic oxides such as ZnO, TiO2, SnO2, BaTiO3, Cu2O, SrTiO3 and KTaO3 is presented. There is interest in achieving ferromagnetism with Curie temperatures above room temperature in such materials for applications in the field of spintronic devices, in which the spin of, the carriers is exploited. The incorporation of several atomic per cent of the transition metals without creation of second phases appears possible under optimized synthesis conditions, leading to ferromagnetism. Pulsed laser deposition, reactive sputtering, molecular beam epitaxy and ion implantation have all been used to produce the oxide-based dilute magnetic materials. The mechanism is still under debate, with carrier-induced, double-exchange and bound magnetic polaron formation all potentially playing a role depending on the conductivity type and level in the material.

ZnO is attracting considerable attention for its possible application to UV light emitters, spin functional devices, gas sensors, transparent electronics and surface acoustic wave devices. There is also interest in integrating ZnO with other wide bandgap ceramic semiconductors such as the AlInGaN system. In this paper we summarize recent progress in doping control, materials processing methods such as dry etching and ohmic and Schottky contact formation, new understanding of the role of hydrogen and finally the prospects for control of ferromagnetism in transition metal-doped ZnO.

A review is given of recent results in developing improved fabrication processes for ZnO devices with the possible application to UV light emitters, spin functional devices, gas sensors, transparent electronics, and surface acoustic wave devices. There is also interest in integrating ZnO with other wide band-gap semiconductors, such as the AlInGaN system. In this article, we summarize recent progress in controlling n- and p-type doping, materials processing methods, such as ion implantation for doping or isolation, Ohmic and Schottky contact formation, plasma etching, the role of hydrogen in the background n-type conductivity of many ZnO films, and finally, the recent achievement of room-temperature ferromagnetism in transition-metal (Mn or Co)-doped ZnO. This may lead to another class of spintronic devices, in which the spin of the carriers is exploited rather than the charge as in more conventional structures.

Photoreflectance studies were made for a series of GaAs1-xNx samples with x less than or equal to 0.01. The photoreflectance studies reveal that the composition dependent bowing parameter of the band gap obtained from the photoreflectance measurements are consistent with those from other optical measurements and also from the first principle supercell calculation. (C) 2003 Elsevier Ltd. All rights reserved.

A review is given here of recent results in developing improved control of growth, doping, and fabrication processes for ZnO devices with possible applications to ultraviolet (UV) light emitters, spin functional devices, gas sensors, transparent electronics, and surface acoustic wave devices. ZnO can be grown on cheap substrates such as glass at relatively low temperatures and may have advantages over the GaN system in some of these applications.

Defects and localized states have been studied for molecular-beam-epitaxy (MBE)-grown high-resistivity and undoped GaAs1-xNx films with a N concentration not exceeding approximately 1.0at.%. The crystalline quality of the films and hence the defects and localized states were determined by high-resolution X-ray diffraction, photoluminescence spectra, capacitance versus voltage measurements and photoinduced Current transient spectra of GaAs and GaAs1-xNx layers. It was concluded that incorporation of low concentrations of N into MBE-grown GaAs1-xNx films promotes the formation of high densities of deep centres similar to EL2 donors, leading to heavy compensation of the films by some unidentified acceptors. GaAs antisite acceptors were believed to be responsible for the said compensation. A prominent defect band near 1.33-1.38eV also appeared to be associated with these defects. The most prominent centres in dilute GaAs1-xN, films with N content less than 0.35 at.% seem to be the EL2 donors and the hole traps located near E-v + 0.3 eV.

The dependence of the fundamental band gap and higher-lying critical-point energies of dilute-nitrogen Ga1−yInyAs1−xNx epilayers on nitrogen mole fraction (x), for x⩽0.0125, and temperature, from 20 to 300 K, was investigated by photoreflectance spectroscopy. The band gap, EG, was found to decrease with increasing x in a highly nonlinear manner. The bowing parameter (the second-order parameter b in a quadratic expression for the dependence of EG on x) was found to become less negative with increasing x; the value of b changed from −50 eV, at very low nitrogen fraction, to −20 eV, at x>0.01. These results strongly suggest that nitrogen-related impurity levels arise within the band gap of dilute-nitrogen Ga1−yInyAs1−xNx alloys.

Electrical and optical activation studies of Si-implanted Al0.25Ga0.75N grown on sapphire substrate have been made as a function of ion dose and anneal temperature. Silicon implantation was done at room temperature with doses of 1 x 10(14) and 1 x 10(15) cm(-2) at 200 keV. The samples were proximity cap annealed from 1200 to 1350 degreesC with a 500-Angstrom-thick AlN cap in a nitrogen environment. The electrical activation efficiencies of 65 and 87% were obtained for the Al0.25Ga0.75N sample implanted with doses of 1 x 10(14) and 1 x 10(15) cm(-2), respectively and annealed at 1350 degreesC for 2 min. The activation efficiency and mobility increase with anneal temperature, indicating an improved implantation damage recovery. The highest mobility obtained from the Si-implanted Al0.25Ga0.75N was 50 cm(2)/Vs for a dose of 1 x 10(15) cm(-2). The increase of photoluminescence intensities of band-edge luminescence and a broad green band was observed as the anneal temperature increases from 1200 to 1350 degreesC, indicating an excellent implantation damage recovery with increasing anneal temperature. (C) 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.