Irina Buyanova

Mechanism for low-temperature photoluminescence in GaNAs/GaAs structures grown by molecular-beam epitaxy

The mechanism for low-temperature photoluminescence (PL) emissions in GaNAs epilayers and GaAs/GaNxAs1 - x quantum well (QW) structures grown by molecular-beam epitaxy is studied in detail, employ ...

Direct determination of electron effective mass in GaNAs/GaAs quantum wells

Electron effective mass (m*e) in GaNxAs1-x/GaAs quantum wells (QWs) is investigated by the optically detected cyclotron resonance technique. The m*e values of 0.12m0 and 0.19m0 are directly determi ...

ZnO Doped With Transition Metal Ions

Spin-dependent phenomena in ZnO may lead to devices with new or enhanced functionality, such as polarized solid-state light sources and sensitive biological and chemical sensors. In this paper, we review the experimental results on transition metal doping of ZnO and show that the material can be made with a single phase at high levels of Co incorporation (~15 at.%) and exhibits the anomalous Hall effect. ZnO is expected to be one of the most promising materials for room-temperature polarized light emission; but to date, we have been unable to detect the optical spin polarization in ZnO. The short spin relaxation time observed likely results from the Rashba effect. Possible solutions involve either cubic phase ZnO or the use of additional stressor layers to create a larger spin splitting in order to get a polarized light emission from these structures or to look at alternative semiconductors and fresh device approaches

Electronic Properties of Ga(In)NAs Alloys

A brief review on the present knowledge of the electronic properties of the Ga(In)NAs ternary and quaternary alloys is given mainly from an experimental perspective. The discussion is focused on Ga(In)NAs with low N composition (< 10 %), where a large amount of experimental work has been done. Important fundamental electronic properties of the material system are analyzed with the emphasis on the nature of the giant band gap bowing in the alloy and nitrogen-induced modifications of the electronic structure of the conduction band. The current knowledge of the key material parameters, relevant for the device applications, such as electron effective mass, recombination processes and band alignment in Ga(In)NAs/GaAs heterostructures, is also reviewed.

Oxygen and zinc vacancies in as-grown ZnO single crystals

Oxygen and zinc vacancies are unambiguously shown to be formed in as-grown ZnO bulk crystals grown from melt without being subjected to irradiation, from electron paramagnetic resonance (EPR) and optically detected magnetic resonance (ODMR) studies. Concentrations of the defects in their paramagnetic charge states V-O(+) and V-Zn(-) are estimated to be similar to 2 x 10(14) cm(-3) and similar to 10(15) cm(-3), respectively. The V-Zn(-) defect is concluded to act as a deep acceptor and to exhibit large Jahn-Teller distortion by 0.8 eV. The energy level of the defect corresponding to the (2-/-) transition is E-v + 1.0 eV. The isolated Zn vacancy is found to be an important recombination centre and is concluded to be responsible for the red luminescence centred at around 1.6 eV. On the other hand, the oxygen vacancy seems to be less important in carrier recombination as it could be detected only in EPR but not in ODMR measurements. Neither isolated V-Zn(-) nor V-O(+) centres participate in the so-called green emission. It is also shown that whereas the concentrations of both defects can be reduced by post-growth annealing, the Zn vacancy exhibits higher thermal stability. The important role of residual contaminants such as Li in the annealing process is underlined.

Wide bandgap GaN-based semiconductors for spintronics

Recent results on achieving ferromagnetism in transition-metal-doped GaN, A1N and related materials are discussed. The field of semiconductor spintronics seeks to exploit the spin of charge carrier ...

Mechanism for rapid thermal annealing improvements in undoped GaNxAs1−x/GaAs structures grown by molecular beam epitaxy

A systematic investigation of the effect of rapid thermal annealing (RTA) on optical properties of undoped GaNAs/GaAs structures is reported. Two effects are suggested to account for the observed dramatic improvement in the quality of the GaNxAs1−x/GaAs quantum structures after RTA: (i) improved composition uniformity of the GaNxAs1−x alloy, deduced from the photoluminescence (PL), PL excitation and time-resolved measurements; and (ii) significant reduction in the concentration of competing nonradiative defects, revealed by the optically detected magnetic resonance studies.

Band gap properties of Zn1- xCdxO alloys grown by molecular-beam epitaxy

Optical absorption and reflectance measurements are performed to evaluate compositional and temperature dependences of band gap energies of Zn1−xCdxO alloys grown by molecular-beam epitaxy. The compositional dependence of the band gap energy, determined by taking into account excitonic contributions, is shown to follow the trend Eg(x) = 3.37−2.82x+0.95x2. Incorporation of Cd was also shown to somewhat slow down thermal variation of the band gap energies, beneficial for future device applications.

Physics and Applications of Dilute Nitrides

Since their development in the 1990s, it has been discovered that diluted nitrides have intriguing properties that are not only distinct from those of conventional semiconductor materials, but also ...

Time-resolved studies of photoluminescence in GaNxP1−x alloys: Evidence for indirect-direct band gap crossover

Time resolved photoluminescence spectroscopy is employed to monitor the effect of N incorporation on the band structure of GaNP alloys. Abrupt shortening in radiative lifetime of near-band gap emissions, arising from excitonic radiative recombination within N-related centers, is found to occur at very low N compositions of around 0.5%, i.e., within the same range as the appearance of the direct-band gap-like transitions in the photomodulated transmission spectra of GaNP reported previously. The effect has been attributed to an enhancement in oscillator strength of optical transitions due to band crossover from indirect to direct-band gap of the alloy.