Reduction of the current gain of the n-p-n transistor component of a thyristor due to the doping concentration of the p-base

The reduction of the current amplification factor of a wide-base transistor, with growing doping concentration in the base region, is investigated. A method for the determination of the minority-carrier lifetime tau /sub n/ in the base region and the emitter Gummel number G/sub e/ is developed. The method is based on transistor structures differing only in the base width. It was found that the lifetime tau /sub n/ decreases according to the power law tau /sub n/ approximately N/sup -0.45//sub A/. This result is analyzed for different recombination processes. Good agreement is obtained if shallow impurities acting as recombination centers are assumed. The injection-limited current gain beta /sub gamma / decreases significantly with an increase in the total number of the doping concentration of the base, reaches a broad maximum, and then falls slowly. The maximum value of G/sub e/ is found to be 1.1*10/sup 14/ cm/sup -4/-s in good agreement with theoretical results. Finally, the contribution of the injection efficiency gamma and the transport factor alpha /sub T/ to the current gain alpha are determined. It is found that alpha is limited mainly by the injection efficiency gamma . >

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