The air mass zero behavior of inversion layer solar cells with a silicon nitride dielectric layerWe propose a quantitative approach to the long-range potential fluctuation model previously developed in disordered 3-D semiconductors. To study how potential modulation modifies the conduction processes in 2-D electron gas, metaI~oxide-semiconductor field-effect transistor structures were irradiated through the gate oxide by an electron beam (20-ke V micro fabricator ) scanning lines parallel or perpendicular to the drain-source axis. The samples were irradiated at various doses for different periods. Irradiation led to a modulation of the oxide and interface charge, resulting in potential valleys and barriers. A shift in the threshold voltage was measured, which depended on the irradiation dose and also on the direction of the lines. The change in electrical properties (threshold voltage Vn mobility) is simply interpreted by a model based on the existence of a conduction threshold. Thus both the range and magnitude of potential fluctuations are investigated using structures with controllable disorder. 5465
We present a quantitative approach to the potential fluctuation model we have previously developed in disordered semiconductors. MOSFET (metal-oxide-semiconductor field-effect transistors) were irradiated along lines parallel (L structures) or perpendicular (T structures) to the drain-source direction, using a 20-keV scanned e-beam. Thus, in the inversion regime, the surface potential ψs was periodically modulated, thereby strongly modifying the conduction processes. Hall measurements were performed as a function of temperature and gate voltage at various irradiation doses and for different periods. Conduction in L structures was influenced by lateral potential barrier scattering, whereas it was barrier controlled in T structures. The experimental results are interpreted by a simple model of energetic distribution of both carrier density n(E) and mobility μ(E), based on the existence of a conduction threshold. When barriers were wide in T structures, Hall measurements showed that part of the carriers did not participate in conductivity in the weak inversion regime, while mixed conduction processes occurred when barriers were narrow. In contrast, all the carriers conducted in the strong inversion regime, and only the mobility was perturbed. Thus the field effect in irradiated MOSFET was used to correlate the Hall carrier density with the conduction threshold energy.
Conductivity and Hall measurements have been carried out on thin silicon films formed by oxygen implantation (SIMOX) and high-temperature annealing. These layers have then been annealed between 450 and 850°C for 1 h in order to study the electrical behavior of oxygen thermal donors (TD). The maximum donor concentration occurs at 550°C for TD-I and 750°C for TD-II. The concentration ofTD-II is higher than that of TO-I and the distribution ofTD-II can be nonuniform. Thermal ionization energies of these donor states are also derived. A TD level (220 mcY) deeper than the typical one (150 meV) is responsible for the electrical properties cfthe SIMOX layers. Subsequent annealing activates shallow TD states and compensation centers. Thus the ionization energy of the deep TD level decreases greatly, when TDs are generated. High carrier mobilities have been measured which have been limited only at low temperatures by interface scattering.
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