<title>Analysis and simulation of the low-temperature performance of Si/SiGe HBTs for the integrated infrared receiver</title>

Abstract

The low temperature current gain and the low frequency noise are important parameters of the preamplifiers of the integrated IR receiver system. Si/Si<SUB>1-x</SUB>Ge<SUB>x</SUB> heterojunction bipolar transistors (HBTs) have potential advantages used in the preamplifiers at low temperature. In this paper, we analyze the characteristics of the current gain and low frequency noise of Si/Si<SUB>1-x</SUB>Ge<SUB>x</SUB>HBTs at low temperature. They are influenced by the following factors: (1) the energy band offset of the emitter-base junction; (2) the high doping effect, the low temperature freeze out effect in the emitter region and base region; (3) the influence of germanium (Ge) content and profile in the base region on the transport performance; (4) the Si/Si<SUB>1-x</SUB>Ge<SUB>x</SUB> interface recombination currents and surface recombination currents; (5) the collector-base heterojunction barrier effect. Then we give the physical analysis model and noise analysis model of Si/Si<SUB>1-x</SUB>Ge<SUB>x</SUB>HBTs at low temperature. Based on this, we present the equivalent circuit and equivalent noise circuit at low temperature and simulate and optimize the characteristics of the current gain and the noise of Si/Si<SUB>1-x</SUB>Ge<SUB>x</SUB> HBT for IR integrated receiver system. The current gain (beta) max equals 300, and the low temperature current gain (beta) max equals 8100 at 77K, at high injection level. We optimize the design of Si/SiGe HBT-based monolithically integrated preamplifier applied to IR receiver system at low temperature.