AlGaAs/GaAs Heterojunction bipolar power transistors

An AlGaAs/GaAs heterojunction bipolar transistor with a total emitter periphery of 320 ¿m has been developed for power amplifier applications. For the base contact, Zn diffusion was used to convert the n-type emitter material into p-type with a doping of ¿1.0 × 1020 cm¿3. Because of the highly doped layer, contact resistivity was extremely low (5 × 10¿7 ¿cm2). At 3 GHz, a CW output power of 320 mW with 7 dB gain and 30% power-added efficiency was obtained. Under pulsed operation, the output power increased to 500 mW with 6 dB gain and 40% power-added efficiency. With further device structure optimisations, the power performance of heterojunction bipolar transistors is expected to rival, or even surpass, that of the GaAs MESFETs.