Time-resolved optical measurements in (110)-oriented GaAs/AlGaAs quantum wells show a tenfold increase of the spin-relaxation rate as a function of applied electric field from 20 to 80 kV cm(-1) at 170 K and indicate a similar variation at 300 K, in agreement with calculations based on the Rashba effect. Spin relaxation is almost field independent below 20 kV cm(-1) reflecting quantum well interface asymmetry. The results indicate the achievability of a voltage-gateable spin-memory time longer than 3 ns simultaneously with a high electron mobility.

Spin splitting in the integer quantum Hall effect is investigated for a series of AlxGa1−xAs/GaAs heterojunctions and quantum wells. Magnetoresistance measurements are performed at mK temperature to characterize the electronic density of states and estimate the strength of many body interactions. A simple model with no free parameters correctly predicts the magnetic field required to observe spin splitting confirming that the appearance of spin splitting is a result of a competition between the disorder induced energy cost of flipping spins and the exchange energy gain associated with the polarized state. In this model, the single particle Zeeman energy plays no role, so that the appearance of this quantum Hall ferromagnet in the highest occupied Landau level can also be thought of as a magnetic field induced Stoner transition.

This letter reports a simple approach to significantly improve the performance of 340nm ultraviolet light emitting diodes (UV-LEDs) on an AlN buffer layer. Greatly improved optical and electrical properties of the 340nm UV-LED have been achieved by using a very thin GaN interlayer (10–20nm), deposited on AlN as a buffer layer directly on sapphire prior to growth of the UV-LED structure. Compared with the UV-LED without the thin GaN interlayer, the output power of the LED with it is increased by a factor of ∼2.2, and the applied bias voltage at 20mA drops from 6.5to∼5V. High resolution transmission electron observation indicates that the thin GaN interlayer can effectively stop the penetration of the dislocations in the AlN buffer layer into the overlaying AlGaN layer, while most of the dislocations in the AlN buffer layer in the UV-LED without the thin GaN interlayer can propagate into the overlying AlGaN layer. Therefore, the enhanced performance of the 340nm UV-LEDs results from a massive reduction in dislocation density in the overlying device structure due to the very thin GaN interlayer. Since it is extremely difficult to reduce the dislocation density in an AlN layer on sapphire, the simple and reliable approach reported in this letter provides a good alternative option to prevent the propagation of dislocations from an AlN buffer into an overlying device structure.

Different dielectrics were used for post-processing surface passivation of AlGaN/GaN heterostructure field-effect transistors (HFETs) and the resulting electrical characteristics examined. An increase in the maximum drain current of approximately 25% was observed after Si3N4 and SiO2 deposition and ~15% for annealed SiO on AlGaN/GaN HFETs. In all cases, the passivation was found to increase the gate leakage current with an observed reduction in the leakage activation energy. However, the rise in gate leakage current was least for SiO. The plasma enhanced chemical vapour deposition method was found not to contribute to the passivation mechanism, whilst the presence of Si appears to be an important factor.