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

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

Magnetophotoluminescence of negatively charged excitons in narrow quantum wells

We present the results of photoluminescence experiments on the negatively charged exciton X- in GaAs/AlxGa1-xAs quantum wells (QW) in high magnetic fields (≤50 T). Three different QW widths are used here: 100, 120, and 150 Å. All optically allowed transitions of X- are observed, enabling us to experimentally verify its energy-level diagram. All samples behave consistently with this diagram. We have determined the binding energy Eb of the singlet and triplet state of X- between 23 and 50 T for the 120 and 150 Å QW, while only the triplet Eb is observed for the 100 Å QW. A detailed comparison with recent theoretical calculations shows an agreement for all samples across this entire field range

Optical imaging of resonant electrical carrier injection into individual quantum dots

We image the micro-electroluminescence (EL) spectra of self-assembled InAs quantum dots (QDs) embedded in the intrinsic region of a GaAs p-i-n diode and demonstrate optical detection of resonant carrier injection into a single QD. Resonant tunneling of electrons and holes into the QDs at bias voltages below the flat-band condition leads to sharp EL lines characteristic of individual QDs, accompanied by a spatial fragmentation of the surface EL emission into small and discrete light- emitting areas, each with its own spectral fingerprint and Stark shift. We explain this behavior in terms of Coulomb interaction effects and the selective excitation of a small number of QDs within the ensemble due to preferential resonant tunneling paths for carriers.Comment: 4 page

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

Resistance Noise Scaling in a Dilute Two-Dimensional Hole System in GaAs

We have measured the resistance noise of a two-dimensional (2D)hole system in a high mobility GaAs quantum well, around the 2D metal-insulator transition (MIT) at zero magnetic field. The normalized noise power $S_R/R^2$ increases strongly when the hole density p_s is decreased, increases slightly with temperature (T) at the largest densities, and decreases strongly with T at low p_s. The noise scales with the resistance, $S_R/R^2 \sim R^{2.4}$, as for a second order phase transition such as a percolation transition. The p_s dependence of the conductivity is consistent with a critical behavior for such a transition, near a density p* which is lower than the observed MIT critical density p_c.Comment: 4 pages, 4 figures, to be published in Phys. Rev. Let