Comparison of DC and high-frequency performance of zinc-doped and carbon-doped InP/InGaAs HBTs grown by metalorganic chemical vapor deposition

Zinc and carbon-doped InP/InGaAs heterojunction bipolar transistors (HBTs) with the same design were grown by metalorganic chemical vapor deposition (MOCVD). DC current gain values of 36 and 16 were measured for zinc and carbon-doped HBTs, respectively, and carrier lifetimes were measured by time-resolved photoluminescence to explain the difference. Transmission line model (TLM) analysis of carbon-doped base layers showed excellent sheet-resistance (828 Ω/□ for 600 A base), indicating successful growth of highly carbon-doped base (2×10¹⁹ cm^-3). The reasons for larger contact resistance of carbon than zinc-doped base despite its low sheet resistance were analyzed. f_T and f_max of 72 and 109 GHz were measured for zinc-doped HBTs, while 70-GHz f_T and 102 GHz f_max were measured for carbon-doped devices. While the best performance was similar for the two HBTs, the associated biasing current densities were much different between zinc (4.0×10 ⁴ A/cm²) and carbon-doped HBTs (2.0×10⁵ A/cm²). The bias-dependant high-frequency performance of the HBTs was measured and analyzed to explain the discrepancy