Transistors such as heterojunction bipolar transistors (HBTs) are widely used in many different applications. For example, one or more HBTs may be provided in a power amplifier (PA) for radio frequency (RF) communications circuitry. As RF communications standards continue to evolve, the performance requirements of RF communications circuitry, and in particular those placed on RF PAs, are becoming increasingly stringent. Accordingly, designers are continually striving to improve RF PA performance parameters such as RF gain and linearity.
To improve the performance of HBTs for RF PAs, designers have previously altered a doping profile of a collector in the device. Generally, these improvements have provided an increase in one performance parameter such as linearity while degrading another such as RF gain. Further, these previous approaches have generally provided improvements in second channel linearity measures such as alternative channel power ratio (ACPR2) and alternative channel leakage power ratio (ACLR2). As discussed above, modern RF communications standards demand high performance across a range of different performance parameters. Accordingly, there is a need for an improved bipolar transistor device.