AlGaAs／GaAs　HBT表面效应的二维数值分析

Two-dimensional Simulation of Surface States Effects on the Performance of AlGaAs/GaAs HBT

采用表面效应集总模型综合考虑表面费米能级钉扎和表面复合效应，对ＡｌＧａＡｓ／ＧａＡｓＨＢＴ表面效应的影响进行了二维数值模拟。结果表明，表面态的存在对集电极电流几乎不产生影响，但显著增加基极电流，使得电流增益明显下降。同时还发现在台面结构ＡＩＧａＡｓ／ＧａＡｓＨＢＴ中外基区表面复合的集边效应，即外基区表面复合主要发生在发射极台面与外基区的交界处附近，与外基区长度基本无关。模拟还表明基区缓变结构可以减少表面复合，提高电流增益。

Using the lumped surface effects model based on Spicer's unified effect model, two-dimensional numerical simulation on AlGaAs/GaAs HBT has been performed to investigate the effects of both surface Fermi level pinning and surface recombination on the current gain of the device. It is shown that the surface recombination in the extrinsic base degrades the current gain significantly. The crowding effect of surface recombination in the extrinsic base has been found. The simulational results also show that the degradation of gain induced by surface effects can be slowed down in a gradual base structure.