A comparison of low-frequency noise characteristics and noise sources in NPN and PNP InP-based heterojunction bipolar transistors

Low-frequency noise characteristics of NPN and PNP InP-based heterojunction bipolar transistors (HBTs) were investigated. NPN HBTs showed a lower base noise current level (3.85 × 10^-17 A²/Hz) than PNP HBTs (3.10 × 10^-16 A²/Hz), but higher collector noise current level (7.16 × 10^-16 A²/Hz) than PNP HBTs (1.48 × 10^-16 A²/Hz) at 10 Hz under I_C=1 mA, V_C=1 V. The NPN devices showed a weak dependence I_C^0.77 of the collector noise current, and a dependence I_B^1.18 of the base noise current, while the PNP devices showed dependences I_C^1.92 and I_B^1.54, respectively. The dominant noise sources and relative intrinsic noise strength were found in both NPN and PNP InP-based HBTs by comparing the noise spectral density with and without the emitter feedback resistor. Equivalent circuit models were employed and intrinsic noise sources were extracted. The high base noise current of PNP HBTs could be attributed to the exposed emitter periphery and higher electron surface recombination velocity in P-type InP materials, while the relatively high collector noise current of NPN HBTs may be due to the noise source originating from generation-recombination process in the bulk material between the emitter and the collector.