Avalanche multiplication and breakdown in AlxGa1-xAs (x < 0-9)

Measurements carried out on thick Al/sub x/Ga/sub 1-x/As (x 0.63

Spin injection in n-type resonant tunneling diodes

We have studied the polarized resolved photoluminescence of n-type GaAs/AlAs/GaAlAs resonant tunneling diodes under magnetic field parallel to the tunnel current. Under resonant tunneling conditions, we have observed two emission lines attributed to neutral (X) and negatively charged excitons (X− ). We have observed a voltage-controlled circular polarization degree from the quantum well emission for both lines, with values up to −88% at 15 T at low voltages which are ascribed to an efficient spin injection from the 2D gases formed at the accumulation layers

Polarization Resolved Luminescence In Asymmetric N -type Gaasalgaas Resonant Tunneling Diodes

We have investigated the polarized emission from a n -type GaAsAlGaAs resonant tunneling diode under magnetic field. The GaAs contact layer emission shows a large constant negative circular polarization. A similar result is observed for the quantum well, but only when electrons are injected from the substrate, while for inverted biases, the polarization tends to become positive for small voltages and large laser excitation intensities. We believe that the quantum well polarization may be associated to the partial thermalization of minority carriers on the well subbands and is thus critically dependent on the bias-controlled density of carriers accumulated in the well. © 2008 American Institute of Physics.9214Hanbicki, A., Van Erve, O.M.J., Magno, R., Kioseoglou, G., Li, C.H., Jonker, B.T., Itskos, G., Petrou, A., (2003) Appl. Phys. Lett., 82, p. 4092Jiang, X., Wang, R., Shelby, R.M., MacFarlane, R.M., Bank, S.R., Harris, J.S., Parkin, S.S.P., (2005) Phys. Rev. Lett., 94, p. 056601Motsnyi, V.F., Van Dorpe, P., Van Roy, W., Goovaerts, E., Safarov, V.I., Borghs, G., De Boeck, J., (2003) Phys. Rev. B, 68, p. 245319Fiederling, R., Keim, M., Reuscher, G., Ossau, W., Schmidt, G., Waag, A., Molenkamp, L.W., (1999) Nature (London), 402, p. 787Ohno, Y., Young, D.K., Beschoten, B., Matsukura, F., Ohno, H., Awschalom, D., (1999) Nature (London), 402, p. 790Oestreich, M.J., Hübner, M.J., Hägele, D., Klar, P.J., Heimbrodt, W., Rühle, W.W., Ashenford, D.E., Lunn, B., (1999) Appl. Phys. Lett., 74, p. 1251Jonker, B.T., Park, Y.D., Bennett, B.R., Cheong, H.D., Kioseoglou, G., Petrou, A., (2000) Phys. Rev. B, 62, p. 8180Braden, J.G., Parker, J.S., Xiong, P., Chun, S.H., Samarth, N., (2003) Phys. Rev. Lett., 91, p. 056602Mattana, R., George, J.-M., Jaffr̀s, H., Nguyen Van Dau, F., Fert, A., Ĺpine, B., Guivarc'H, A., J́źquel, G., (2003) Phys. Rev. Lett., 90, p. 166601Gruber, T., Keim, M., Fiederling, R., Reuscher, G., Ossau, W., Schmidt, G., Molenkamp, M., Waag, A., (2001) Appl. Phys. Lett., 78, p. 1101Slobodskyy, A., Gould, C., Slobodskyy, T., Becker, C.R., Schmidt, G., Molenkamp, L.W., (2003) Phys. Rev. Lett., 90, p. 246601De Carvalho, H.B., Galvão Gobato, Y., Brasil, M.J.S.P., Lopez-Richard, V., Marques, G.E., Camps, I., Henini, M., Hill, G., (2006) Phys. Rev. B, 73, p. 155317De Carvalho, H.B., Brasil, M.J.S.P., Galvão Gobato, Y., Marques, G.E., Galeti, H.V.A., Henini, M., Hill, G., (2007) Appl. Phys. Lett., 90, p. 062120Dos Santos, L.F., Galvão Gobato, Y., Marques, G.E., Brasil, M.J.S.P., Henini, M., Airey, R., (2007) Appl. Phys. Lett., 91, p. 073520Snelling, M.J., Blackwood, E., MacDonagh, C.J., Harley, R.T., Foxon, C.T.B., (1992) Phys. Rev. B, 45, p. 392

Fock-Darwin-like quantum dot states formed by charged Mn interstitial ions

We report a method of creating electrostatically induced quantum dots by thermal diffusion of interstitial Mn ions out of a p-type (GaMn)As layer into the vicinity of a GaAs quantum well. This approach creates deep, approximately circular, and strongly confined dotlike potential minima in a large (200  μm) mesa diode structure without need for advanced lithography or electrostatic gating. Magnetotunneling spectroscopy of an individual dot reveals the symmetry of its electronic eigenfunctions and a rich energy level spectrum of Fock-Darwin-like states with an orbital angular momentum component |lz| from 0 to 11

Second-harmonic generation from monolayer and multilayer Langmuir-Blodgett films

SIGLEAvailable from British Library Document Supply Centre-DSC:DXN011711 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Second-harmonic generation from monolayer and multilayer Langmuir-Blodgett films

SIGLEAvailable from British Library Document Supply Centre-DSC:DXN011711 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Characterisation of defects in p-GaN by admittance spectroscopy

Mg-doped GaN films have been grown on (0 0 0 1) sapphire using metal organic vapour phase epitaxy. Use of different buffer layer strategies caused the threading dislocation density (TDD) in the GaN to be either approximately 2×109 cm−2 or 1×1010 cm−2. Frequency-dependent capacitance and conductance measurements at temperatures up to 450 K have been used to study the electronic states associated with the Mg doping, and to determine how these are affected by the TDD. Admittance spectroscopy of the films finds a single impurity-related acceptor level with an activation energy of 160±10 meV for [Mg] of about 1×1019 cm−3, and 120±10 eV as the Mg precursor flux decreased. This level is thought to be associated with the Mg acceptor state. The TDD has no discernible effect on the trap detected by admittance spectroscopy. We compare these results with cathodoluminescence measurements reported in the literature, which reveal that most threading dislocations are non-radiative recombination centres, and discuss possible reasons why our admittance spectroscopy have not detected electrically active defects associated with threading dislocations

Characterization of defects in Mg doped GaN epitaxial layers using conductance measurements

Mg-doped GaN films have been grown on sapphire by metalorganic vapour phase epitaxy. Two different buffer layer schemes between the film and the sapphire substrate were used, giving rise to differing threading dislocation densities (TDDs) in the GaN. Frequency-dependent capacitance and conductance measurements have been used to study the electronic states associated with the Mg doping, and to determine how these are affected by the TDD. Current–voltage and admittance spectroscopy measurements were carried out using Al/Au Schottky contacts and Ni/Au Ohmic contacts fabricated in a dot-and-ring pattern. Frequency-dependent measurements on these devices were corrected to remove the series resistance effects arising from the well known high resistivity of Mg-doped GaN using formulae derived from the equivalent parallel circuit model. Thermal admittance spectroscopy, in which the conductance is monitored as a function of temperature, verified the existence of a single impurity-related acceptor level in samples with different TDDs at 165 ± 10 meV. For all of the samples the extrapolated capture cross-section values were very small, in the range of ~ 10− 20 cm− 2, suggesting that the acceptor level could be very repulsive. Since admittance spectroscopy detects only majority carrier traps, we believe these defect signature values are most probably associated with the Mg acceptor state as they are very close to the results previously reported by other research groups using different techniques

Demonstration of Photon Coupling in Dual Multiple-Quantum-Well Solar Cells

Multiple-quantum-well (MQW) top cells can enhance the performance of multi-junction solar cells since the absorption edge of top and middle subcells can be tuned with the MQWs to maximize the efficiency. The radiative dominance of MQW top cells can enhance photon coupling, which can potentially reduce the spectral sensitivity of the device and, thus, raise the energy harvest. We present experimental results on photon coupling in dual-junction cells with GaInP top cells containing GaInAsP quantum wells along with theoretical calculation based on a detailed balance model. It is observed that at high concentration, approximately 50% of the dark current of an MQW top cell is transferred to the photocurrent of the cell in the bottom, which is much higher than any previously reported values.Lee, K.; Barnham, K.; Connolly, JP.; Browne, B.; Airey, R.; Roberts, J.; Fuhrer, M.... (2012). Demonstration of Photon Coupling in Dual Multiple-Quantum-Well Solar Cells. IEEE Journal of Photovoltaics. 2(1):68-74. doi:10.1109/JPHOTOV.2011.2177444S68742