A filamentary structure has been used to compare the electrical properties of a germanium surface with those of an adjacent p-n junction intersecting the same surface. Surface charge is varied by field effect plates in the isolated portion of the filament and near the junction. An orderlv relation can be found between surface potential variations and changes in the reverse currents across the jun"ction. At low bias, the junction current varies with surface recombination velocity, and for bias near breakdown, the breakdown voltage varies with induced charge at the surface. For inverted surfaces, the low bias current varies rapidly as expected from channel length variations. With inverted surfaces, channel growth leads to large reverse current variations with surface potential, but breakdown voltage becomes independent of surface charge. These variations are considered in terms of simple theory, and device implications are discussed.
A method is presented for controlling the reverse breakdown voltage (VB) in a silicon graded junction. The significant process parameters are shown to be resistivity, time of diffusion, and temperature of diffusion. For a constant resistivity, VB increases with the fourth root of the time of diffusion and with the square root of the depth of diffusion as predicted by theory. Statistical analysis shows that the mean breakdown voltage for a large group of units can be predicted within 2%. The method fails for very low or high resistivity material.
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