Oxygen precipitate behavior of nitrogen-doped Czochralski-grown silicon (CZ-Si) crystals is investigated. It is found that nitrogen doping enhances oxygen precipitation after heat treatment. The oxygen precipitate volume density in nitrogen-doped crystals after heat treatment does not change regardless of the heat treatment temperature, while the oxygen precipitate volume density of crystals which are not nitrogen doped decreases as the heat-treatment temperature increases. The characteristics of precipitation behavior in nitrogen-doped CZ-Si crystals are due to the “grown-in” oxygen precipitates, which already exist in an as-grown state with a high volume density. The oxygen precipitation growth of nitrogen-doped crystals is found to be an oxygen diffusion limited process, the same as in the case of the oxygen precipitation growth of crystals which are not nitrogen doped. The formation mechanism of grown-in oxygen precipitates will also be discussed in this article.
Abstract-A gate insulating layer with single nm-order thickness for suppressing gate leakage current is one of the key factors in extending downsizing limits, based upon the scaling rule, of field-effect-type transistors. We describe the fabrication and characterization of GaAs MISFETs with a nm-thin oxidized layer as the gate insulating layer, which is formed by an ultraviolet (UV) and ozone process. The UV and ozone process forms oxidized GaAs layers near the surface, which effectively suppress the reverse leakage current by several orders of magnitude. The fabricated GaAs MISFET can operate not only in the depletion mode, but also in the accumulation mode up to 3 V of the gate voltage for 8-nm-thick oxidized layer due to the current blocking effect of the oxidized layer. A current cutoff frequency of 6 GHz and a maximum oscillation frequency of 8 GHz are obtained for a GaAs MISFET with a 1-m-long gate length and 8-nm-thick oxidized layer.Index Terms-Compound semiconductors, GaAs, MISFET, selfalign, ultraviolet (UV) and ozone process.
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