Investigation of gallium indium phosphide/gallium arsenide double heterojunction bipolar transistors for microwave power amplifier applications

Heterojunction Bipolar Transistors (HBTs) fabricated with the AlGaAs/GaAs material system are presently being successfully applied to power amplifiers for wireless communication handsets. For future use, a variety of device improvements would be worthwhile, including reduced offset voltage, greater ruggedness, and higher gain in high efficiency modes of operation. In this thesis, the characteristics of GaInP/GaAs/GaInP Double Heterojunction Bipolar Transistors (DHBTs), in which Gah1P is used for both the emitter and collector of the device, are investigated in relation to microwave power amplifier applications. The design, fabrication, DC and high frequency electrical characteristics, and thermal characteristics of the DHBTs are studied. Saturation charge storage in the devices is investigated for the first time. Several novel amplifier configurations which exploit the unique characteristics of the DHBTs are proposed.; Several lots of GaInP/GaAs DHBTs were fabricated for this work with both self-align and non-self-aligned techniques. It was shown that high base collector geometry devices in this work have shown cut-off frequency (f _T) as high as 70GHz, which is the highest to date for GaInP/GaAs DHBTs.; Thermal effects are also important considerations in designing transistors for power applications. A novel heatsinking technique was proposed and implemented in this work. This technology combines the flip-chip approach and through-substrate via holes, to use the front side of the HBT substrate as the heatsink and the backside of the wafer for interconnect. The thermal resistance was reduced by 5 times.; The hole barrier at the base collector junction of the DHBT prevents hole injection into the collector during the saturation regime of the transistor operation. This was shown for the first time in GaInP/GaAs DHBTs, using a novel technique to determine the charge storage behavior of a heterojunction.; To demonstrate the microwave gain and power output capability of the GaInP/GaAs DHBTs, load pull measurements were performed. A unit cell with aggregate emitter area of 896μm2 was demonstrated to provide 250mW output power with >50% power added efficiency. The relationship between the biasing scheme and the loadpull results was examined. Several switching amplifier architectures that take advantage of the fast switching ability of the DHBTs were also proposed.