We present a detailed study of the electron-LO phonon interaction in a triple quantum well structure, which acts as the active region in an intersubband terahertz emitter. The phonon modes of the heterostructure were calculated using a transfer matrix method within the framework of the dielectric continuum model. Unlike earlier calculations that approximate phonon emission rates using bulk-like phonon modes, we exploit the presence of specific interface and layer-confined phonon modes. The electronic levels are designed to be in resonance with one of the phonon modes for optimizing phonon-scattering rates and to enhance device performance. Our calculations indicate that it is beneficial to utilize the higher energy interface phonon modes rather than the confined phonon modes for faster depopulation in a three level lasing scheme. Scattering rates for two different designs were computed to establish the above result.
Attenuated total reflection is commonly used to excite the surface plasma wave (SPW) on a metal film. The SPW traveling on the surface of the metal will enhance the emission of photoelectrons from the metal into the semiconducting region of a Schottky barrier photodiode. A model consisting of an aluminum film on n-type gallium arsenide forming a Schottky barrier photodiode is used to predict the enhanced emission of photoelectrons over the barrier between the aluminum film and the gallium arsenide. The quantum efficiency for this model shows a strong dependence on parameters such as the electron escape depth, film thickness, and the spacer thickness between the prism coupler and the photodiode. The model proved to be effective when used to fit quantum efficiency and reflectivity data resulting from an angle scan experiment.
The production and removal of carbon-related defects have been investigated in 1-MeV electron-irradiated boron-doped silicon solar cells using deep level transient spectroscopy (DLTS). In Czochralski (CZ) material, the interstitial carbon defect (hole trap at Ev+0.27 eV), CI, decays by thermal and charge injection processes. We find that irradiation by MeV electrons creates CI while simultaneously removing it through the minority-carrier injection process. Removal of CI correlates with significant growth in the density of a complex reportedly consisting of carbon and oxygen (hole trap at Ev+0.38 eV). Thermal annealing produces a different DLTS signal than does minority-carrier injection indicating that the carbon and oxygen complex (C+O) is at least two species. The effective cross section for minority-carrier-induced annealing of CI is found to be 2×10−18 cm2 in these samples.
An aluminum on n-type gallium arsenide Schottky diode with a prism coupler on the front face was illuminated by a p-polarized Nd:YAG laser to excite the surface plasma resonance in the aluminum barrier contact. The internal photoemission current and reflectance were measured simultaneously as a function of the angle of incidence. The excitation of the surface plasma resonance was observed by a dip in the reflectance which occurred at the same angle as a peak in the photoemission current. These effects disappeared in the case of s-polarization. Enhancement in the photoemission current by as much as a factor of 3 was obtained.
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