We demonstrate control by applied electric field of the charge states in single self-assembled InP quantum dots placed in GaInP Schottky structures grown by metalorganic vapor phase epitaxy. This has been enabled by growth optimization leading to suppression of formation of large dots uncontrollably accumulating charge. Using bias-and polarization-dependent micro-photoluminescence, we identify the exciton multi-particle states and carry out a systematic study of the neutral exciton state dipole moment and polarizability. This analysis allows for the characterization of the exciton wavefunction properties at the single dot level for this type of quantum dots. Photocurrent measurements allow further characterization of exciton properties by electrical means, opening new possibilities for resonant excitation studies for such system. arXiv:1107.2522v1 [cond-mat.mes-hall]
New types of detectors based on the wide band gap material AlGaAs have been developed for soft X-ray spectroscopy applications. We report on the spectroscopic performance of simple p-i-n diodes and avalanche photodiodes (APDs). A number of diode types with different layer thicknesses have also been characterised. X-ray spectra from 55 Fe and 109 Cd radioactive sources show these diodes can be used for spectroscopy with promising energy resolution (1.0-1.25 keV) over a -30 to +90 • C temperature range. The temperature dependence of the avalanche multiplication process at soft X-ray energies in Al 0.8 Ga 0.2 As APDs was also investigated at temperatures from -20 to +80 • C. The temperature dependence of the pure electron initiated multiplication factor (M e ) and the mixed carrier initiated avalanche multiplication factor (M mix ) were extracted from the X-ray spectra. The experimental results are compared with a spectroscopic Monte Carlo model for Al 0.8 Ga 0.2 As diodes from which the temperature dependence of the pure hole initiated multiplication factor (M h ) is determined.Monte Carlo simulations for the avalanche gain of absorbed X-ray photons have also been developed to study the relationship between avalanche gain and energy resolution for semiconductor X-ray avalanche photodiodes. The model showed that the distribution of gains, which directly affects the energy resolution, depends on the number of injected electron-hole pairs (and hence the photon energy), the relationship between the two ionization coefficients, and the overall mean
We demonstrate a semiconductor PCSEL array that uniquely combines an in-plane waveguide structure with nano-scale patterned PCSEL elements. This novel geometry allows two-dimensional electronically controllable coherent coupling of remote vertically emitting lasers. Mutual coherence of the PCSEL elements is verified through the demonstration of a two-dimensional Young’s Slits experiment. In addition to allowing the all-electronic control of the interference pattern, this type of device offers new routes to power and brightness scaling in semiconductor lasers, and opportunities for all-electronic beam steering.
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