Abstract
This paper presents the heavy doping effects on the injection current characteristics in p-n-p transistors with a heavily doped but thin base region. The results of the present study indicate that 1) at room temperature the hole current injected into heavily doped base is insensitive to the impurity compensation effect, 2) a linear relationship between the base sheet resistance and the collector-current density is observed when the base doping density is under 1 × 1019 cm−3. This relationship becomes supralinear as the doping density further increases. As a result, useful current gain exists in thin base transistors even when the base doping is greater than 1 × 1019 cm−3. From the collector-current-base sheet-resistance relationship and the base doping profile, the effective intrinsic carrier density as a function of the doping density is evaluated and found to increase 8.7 times over that of pure silicon, when the average doping density is 5 × 1019 cm−3 (maximum doping density 1 × 1020 cm−3). 3) The collector current and the current gain of the transistors become less sensitive to the temperature as the base doping density increases. We had observed a current gain up to 30 at 77 K for transistors with the maximum base doping density in the 1018 cm−3 range. The transistors with lower base doping suffer much more degradation in current gain when the temperature is lowered to 77 K. Copyright © 1980 by The Institute of Electrical and Electronics Engineers, Inc.