No description available.

The non-equilibrium operation of narrow energy-gap semiconductor devices has been studied in the context of infrared detection. The fundamental mechanisms which determine medium and long wavelength infrared detector sensitivities have been reviewed, and it is proposed that the dominant factors which have necessitated the cooling of such devices in order to minimise thermal noise can be suppressed. This is contrary to previous assumptions, and is a consequence of the operation of detectors in a non-equilibrium mode where the free carrier densities are held substantially below their normal values. The prospect is offered, therefore, of the removal of the cooling requirement with less than a factor of two loss in performance. The properties of non-equilibrium minority carrier current phenomena in wide-gap semiconductors have been reviewed. The first application of these phenomena to narrow-gap devices is presented here and, specifically, the effects of minority carrier accumulation, exclusion and extraction in cadmium mercury telluride infrared detectors are demonstrated. Accumulation has been studied in swept-out extrinsic devices, where it has been shown that the responsivity can be increased by a factor of five, without loss of frequency response. Consequently, the SPRITE photoconductors have been re-designed to optimise the effects of accumulation, giving a 50% Improvement in spatial resolution. Minority carrier exclusion has been examined in intrinsic devices, where non-equilibrium carrier reductions by a factor of forty have been demonstrated at room temperature, with electric fields sufficiently low to prevent carrier heating. Increases in responsivity of up to a factor of twenty and improvements in detectivity by a factor of three have been observed, confirming that the dominant Auger generation mechanism can be suppressed. Observation of the maximum performance improvement was prevented, however, by excess surface generation and 1/f noise. Photovoltaic devices for the suppression of Auger generation through the use of extraction have been described, and the phenomena has been demonstrated at room temperature. Bipolar transistor operation has also been demonstrated for the first time in CMT. This was observed both under low temperature, extrinsic conditions and near ambient temperature where performance is maintained by extraction.

<p>An <em>isotype heterojunction</em> is a junction between two layers of dissimilar semiconductors both of which are doped either n-type or p-type. These semiconductor structures are found in a variety of optoelectronic devices, such as solar cells, semiconductor lasers, and detectors. Motivated by the structure of third generation inorganic solar cells, this thesis concentrates on the analytical modelling of isotype heterojunctions and its application to the design optimization of these devices. The main development of this work is the introduction of an analytical expression for the current density across an isotype heterojunction valid for arbitrary doping concentration ratios. This result generalizes the standard expression found in the literature, which is limited by the assumption that the doping concentration ratio between the two sides of the heterojunction is equal to one. The generalization is developed by employing the Lambert W function in the solution of the electrostatic boundary condition associated with the heterojunction interface. As done in the derivation of the standard expression found in the literature, the generalization only considers thermionic emission, but the same method can readily be applied for other transport mechanisms. A key feature of this generalized result is that it mathematically contains the expression for the current density across a metal-semiconductor Schottky contact as a limiting case, thereby unifying the treatment of these two heterointerfaces into a single general analytical description. This latter find is particularly significant from a theoretical perspective, considering that the two heterointerfaces are traditionally described as separate topics in the presentation of semiconductor device theory.</p> / Master of Applied Science (MASc)

Silicon carbide is a semiconductor with a wide bandgap of up to 3.2 eV and is capable of operating in extreme conditions, high temperature and high energy modes. This work focuses on the investigation of electrical and optical properties of monocrystalline SiC by various methods including Raman spectroscopy, volt-ampere characteristics, L-TCT and spectroscopic techniques. The adhesion of contacts and the influence of different contact materials on the ability to detect ionizing radiation are also studied to optimize the technology of preparation of quality SiC-based radiation detectors.

No description available.

Das Verhalten der elektronischen Eigenschaften von gespaltenen, aus der Schmelze gezüchteten In2O3-(111) Kristallen wurde bei Deposition von Edelmetallen, In und Sn mittels winkelaufgelöster Photoelektronen-Spektroskopie untersucht. Die Stöchiometrie, strukturelle Qualität und Kristall-Orientierung, die Oberflächenmorphologie und die Elektronenkonzentration wurden jeweils mittels energiedispersiver Röntgenspektroskopie, Laue-Beugung, Raster Tunnel-Mikroskopie (STM) und Hall-Effekt untersucht. Die Ähnlichkeit der fundamentalen und Oberflächen-Bandlücken kann auf das fast flache Verhalten der Bänder auf der gespaltenen Oberfläche der Kristalle zurückgeführt werden. Die Grenzflächen von Ag und Au/In2O3 zeigen Schottky-Verhalten, während ein ohmscher in Cu, In und Sn /In2O3-Kontakten beobachtet wurde. Aufgrund der Übereinstimmung zwischen optischen und Oberflächen-Bandlücken, der Bildung eines Gleichrichterkontaktes und des Auftretens der Oberflächenphotospannung auf der frischen Kristalloberfläche kann gefolgert werden, dass SEAL nicht eine intrinsische Eigenschaft der gespaltenen Oberfläche der untersuchten Kristalle ist. Des Weiteren wurden bei dicker Au- und Cu-Beschichtung von In2O3 bei Raumtemperatur Shockley-artige Oberflächenzustände beobachtet. Zusätzlich wurde die erste Phase des Wachstums von Cu und In auf In2O3 von der Ausbildung eines 2-dimensionalen Elektrongases (2DEG) begleitet, welches bei dickeren Schichten verschwand, die von dem auf reinen Oberflächen von dünnen In2O3- Filmen gemessenen 2DEG verschieden sind. Nach Messung der Austrittarbeit von In2O3 und den jeweils untersuchten Metallen in situ und unter Verwendung der Schottky-Mott-Regel trat außer bei Ag/In2O3 eine deutliche Abweichung auf. Die experimentellen Ergebnisse stimmen auch mit fortgeschrittenen Theorien, die auf dem Elektronegativitätskonzept und MIGS–Modellen basieren, nicht überein. / The behavior of the electronic properties of as-cleaved melt-grown In2O3 (111) single crystals was studied upon noble metals, In and Sn deposition using angle-resolved photoemission spectroscopy. The stoichiometry, structural quality and crystal orientation, surface morphology, and the electron concentration were examined by energy dispersive X-ray spectroscopy, Laue diffraction, scanning tunneling microscopy (STM), and Hall-effect measurement, respectively. The similarity of the measured-fundamental and surface-band gaps reveals the nearly flat behavior of the bands at the as-cleaved surface of the crystals. Ag and Au/In2O3 interfaces show Schottky behavior, while an ohmic one was observed in Cu, In, and Sn/In2O3 contacts. From agreement of the bulk and surface band gaps, rectifying contact formation as well as the occurrence of photovoltage effect at the pristine surface of the crystals, it can be deduced that SEAL is not an intrinsic property of the as-cleaved surface of the studied crystals. Moreover, for thick Au and Cu overlayer regime at room temperature, Shockley-like surface states were observed. Additionally, the initial stage of Cu and In growth on In2O3 was accompanied by the formation of a two dimensional electron gas (2DEG) fading away for higher coverages which are not associated with the earlier-detected 2DEG at the surface of In2O3 thin films. The application of the Schottky-Mott rule, using in situ-measured work functions of In2O3 and the metals, showed a strong disagreement for all the interfaces except for Ag/In2O3. The experimental data also disagree with more advanced theories based on the electronegativity concept and metal-induced gap states models.