A Microwave SPICE Model For Double Heterojunction Bipolar Transistors

A SPICE model for Double-Heterojunction Bipolar Transistors@HBTs) has been developed which can account for bias-dependent barrier effects of both the emitter and collector junctions. The simulated dc and microwave performances agree well with the measured data. Introduction InP-based HBTs are promising microwave power devices mainly due to their better thermal conductivity, current gain, and carrier transport than that of Gas-based devices[l]. Incorporating a broad-band collector spacer layer the device shows a higher breakdown voltage, typically 11 V, which is essential for power operation. Recently, we demonstrated the first microwave power operation of an InP/InGaAs/InP double heterojunction bipolar transistor @HBT)[2]. For DHBT optimization and circuit application, it is necessary to develop a model[3] that can account for bias-dependent barrier effects at both emitter and collector junctions. In this paper, we present a SPICE model which is based on a physical model of the devices. DC and microwave small-signal as well as large signal behaviors are simulated and compared with the experimental results. The good agreement between the two confirms the validity of the model. Device Model Figure 1 shows the banddiagram of two types of DHBTs to be modeled. They are: a DHBT with an undoped InGaAs spacer layer at the C-B junction (type I) and a DHBT with n'-InP layer at the InP collector region (type 11). DC and RF transport equations for a DHBT have been derived in the literature[4,5], with the assumption that the base transport is diffusive and the injection via junction barriers is dominated by thermionic emission. We have derived a small-signal admittance matrix based on a small-signal analysis. Its equivalent circuit was obtained from a zero-pole analysis. The details will be presented elsewhere. i