Low-frequency noise characteristics of p-n-p InAlAs/InGaAs HBTs

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 /spl times/ 10/sup -16/ A/sup 2//Hz) was found to be higher than the collector noise current spectral density (1.48 /spl times/ 10/sup -16/ A/sup 2//Hz) at 10 Hz under low bias condition (I/sub C/=1 mA, V/sub EC/=1 V), while the base noise current spectral density (2.04 /spl times/ 10/sup -15/ A/sup 2//Hz) is lower than the collector noise current spectral density (7.87 /spl times/ 10/sup -15/ A/sup 2//Hz) under high bias condition (I/sub C/=10 mA, V/sub EC/=2 V). The low-frequency noise sources were identified using the emitter-feedback technique. The results suggest that the low-frequency noise is a surface-related process. In addition, the dominant noise sources varied with bias levels.