The Study of Thermal Effect and Frequency Characteristics on Heterojunction power bipolar transistors

• Main Authors: K.H.Ho, 何國華
• Other Authors: Y.H.Wang,M.P.Houng
• Format: Others
• Language: en_US
• Published: 1994
• Online Access: http://ndltd.ncl.edu.tw/handle/83617473076943658915

碩士 === 國立成功大學 === 電機工程研究所 === 82 === The Heterojunction wide-gap emitter provides a large barrier to emitter reverse current and so allows the base region to be heavily doped, and therefore lower in resistance than for a homojunction transistor. The general view is that the lower base resistance obviously results in a substantially improved frequency response. Hence, HBTs based on Npn AlGaAs/GaAs material system have attracted considerable attention for microwave power and digital application due to their high speed and high current handling capabilities. In the thesis, an analytical model based on the Npn AlGaAs/GaAs HBT structure for carrier transport is present. The numerical simulation analyze the I-V characteristics of the HBT, and optimizing the device structure and parameters to increase the current gain. We also present the calculation for the high frequency performance. Two figures of merit of power HBT operation : cut-off and maximum oscillation frequency are calculated. Besides, thermal instability is a phenomenon peculiar important to power HBT, since GaAs has a smaller thermal conductivity (Ks=0.47 W/(cm‧ K)) than Si BJT (Ks=1.45) .The heat generated in the device was hard to dissipated then increase the junction temperature, thus cause self-destruction of the transistor. Therefore an iso- thermal HBT model is derived to calculate the junction temperature, I-V characteristics, and frequency response when to achieve a more realistic power HBT model.