The low-frequency noise characteristics of p-n-p InAlAs/InGaAs heterojunction bipolar transistors (HBTs) were investigated. Devices with various geometries were measured under different bias conditions. The base noise current spectral density (3.11 × 10-16 A2/Hz) was found to be higher than the collector noise current spectral density (1.48 × 10-16 A22/Hz) at 10 Hz under low bias condition (Ic = 1 mA, VEC = 1 V), while the base noise current spectral density (2.04 × 10-15 A2/Hz) is lower than the collector noise current spectral density (7.87 × 10-15 A2/Hz) under high bias condition (Ic = 10 mA, VEC = 2 V). The low-frequency noise sources were identified using the emitter-feedback back technique. The results suggest that the low-frequency noise is a surface-related process. In addition, the dominant noise sources varied with bias levels.
