The intrinsic carrier density in silicon has been measured by a novel technique based on low-frequency capacitance measurements of a p+-i-n+ diode biased in high injection. The major advantage of the method is its insensitivity to uncertainties regarding the exact values of the carrier mobilities, the recombination parameters, and the doping density. The intrinsic carrier density was measured in the temperature range from 78 to 340 K. At 300 K the value of ni was found to be (9.7±0.1)×109 cm−3.
Tungsten oxide thin films were grown by chemical vapor deposition at low pressure (0.1 Torr) and at temperatures ranging between 450 and 600°C, in a cold wall horizontal reactor by pyrolysis of W(CO), vapors. A small air flow through the reactor induces the growth of remarkably well-textured polycrystalline W03 films, oriented with the <010> crystallographic axis perpendicular to the substrate as shown by x-ray diffraction and atomic force microscopy measurements.The films were grown on silicon wafers covered by SiO,, Si3N4, and polycrystalline silicon; the film texture was not influenced by the nature of the substrate. In the absence of oxygen during deposition the x-ray diffraction patterns show peaks corresponding to W,O (beta-tungsten) and to body centered cubic tungsten. These films exhibited metallic or insulating properties depending on the deposition temperature, as determined by resistivity measurements within the range 77 to 350 K. The metallic character was enhanced at lower temperatures. After thermal annealing of these films at 1000°C for 10 s in medium vacuum (2 >< 10-2 Torr) their character changed to purely metallic. The x-ray diffraction patterns taken after annealing show peaks corresponding to body centered cubic W and W02.
The electron and hole mobilities were measured between 78 and 340 K. The method used is based on the frequency dependence of the conductance and the capacitance of a high resistivity diode biased in high injection. The method is insensitive to uncertainties regarding the ionized dopant densities. In the temperature range from 170 to 340 K the carrier mobilities vary as T−a, where a=2.34±0.08 for electrons while for holes a=2.85±0.05. At 77.8 K the hole mobility is 14000±400 cm2/V s while the electron mobility is 24000±800 cm2/V s.
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