为了得到晶体管中高的电流放大系数,重要的是使注入少子电流与总发射极电流之比γ接近于1,或使称做注入损失的量1-γ尽可能小。已经表明,如果发射区比基区有较宽的禁带宽度,则发射极注入损失可以阵低几个数量级。通常采用高发射极掺杂浓度,以使电流增大,而α不致下降;或者降低高的发射极掺杂浓度,而得到较小的发射极电容。在高频晶体管中,减小发射极电容可被用来展宽频率范围或通过增大面积而提高功率能力。 In order to obtain a high current amplification factor in the transistor, it is important to make the ratio [gamma] of the injected minority sub-current to the total emitter current be close to 1, or to minimize the amount 1-y of the injection loss. It has been shown that if the emitter region has a wider bandgap than the base region, the emitter implant loss can be several orders of magnitude lower. Normally high emitter dopant concentration is used to increase the current without decreasing α, or by reducing the high emitter dopant concentration and resulting in a smaller emitter capacitance. In high frequency transistors, reducing the emitter capacitance can be used to broaden the frequency range or to increase power capability by increasing area.