EXPERIMENTAL INVESTIGATION OF LOW-FREQUENCY NOISE PROPERTIES OF ALGAAS/GAAS AND GAINP/GAAS HETEROJUNCTION BIPOLAR-TRANSISTORS

The intrinsic low frequency noise characteristics of AlGaAs/GaAs and GaInP/GaAs HBTs have been studied. HBTs with large emitter size of 120 x 120 mu m(2) have been fabricated on MOCVD-grown abrupt junction emitter materials without undoped spacer layer. The leakage current of GaInP/GaAs HBTs is a little lower than that of AlGaAs/GaAs HBTs. However, AlGaAs/GaAs HBTs have 10 similar to 25 dB lower noise level than GaInP/GaAs HBTs. For GaInP/GaAs HBTs, the base current noise power spectral densities are proportional to similar to exp(V-BE/V-T) at a low current level(Ic less than or equal to 1mA) and saturate at a high current level. This is due to the gain-creeping effect of HBT originating from the persistent band discontinuity. Thus, the dominant noise generation process occurs at the base side of hetero-interface, which is very noisy. But AlGaAs/GaAs HBT noise source is the recombination at the base region.