The power performance of InP based single HBTs has been mediocre compared with their double HBTs counterparts due to their inherently low breakdown voltage. For power amplifiers requiring moderate output power levels, single HBTs are more cost effective due to their simplicity of fabrication and design. InP-based single HBTs have demonstrated power performance at 10 GHz of 1.37 mW/μm2, 11 dB gain and 33.9% power-added-efficiency. In this work, a graded InAlAs/InGaAs emitter base junction and a low-doped thick collector was employed to lower the turn-on voltage and increase the breakdown voltage respectively. InAlAs/InGaAs single HBTs were subsequently fabricated with undercut collectors for reduced base-collector capacitance. A 4-finger 2×10 μm2 HBT unit cell exhibited 22.5 dBm continuous wave (CW) output power (2.23 mW/μm2 power density), 35% power-added-efficiency and an associated gain of 10.5 dB at 10 GHz. To our knowledge, this is the best output power density performance for InP based single HBTs.
