Characterization of diode-connected heterojunction bipolar transistors for near-infrared detecting applications

The characterization of SiGe diode-connected heterojunction bipolar transistors (HBTs) through measurements of two-circuit configurations is presented. Characterization is done to understand the behavior of these diodes for near-infrared detecting applications at room temperature and 77 K. The two configurations that are considered differ; the first is a base-emitter shorted HBT and the second is a base-collector shorted HBT. The parameters measured are current density-voltage, capacitance-voltage, and noise. The two configurations are implemented using the austriamicrosystems AG 0.35-μm process. The base-emitter shorted configuration exhibits a flatter J_C versus V curve when in reverse bias compared with the base-collector configuration. The C - V curves are the same for both configurations. The noise voltage of the base-emitter configuration is 36 and 14.48 μV / Hz at 102.5 Hz for 293 and 77 K temperature points, respectively, to 14.48 and 12.42 μV / Hz at 50 kHz for 293 and 77 K, respectively. The noise voltage for the base-collector configuration is 12.6 and 7.56 μV / Hz at 102.5 Hz for 293 and 77 K, respectively, to 2.228 and 5.981 μV / Hz at 50 kHz for 293 and 77 K, respectively. This work is done using a standard Si-based technology, where a detector array with readout circuitry can be prototyped as a single chip. The floating base transistor topology is analyzed and used as a foundation for this work. The characteristics of a floating base configuration result in a wide depletion region, large-series resistance, and small-series capacitance. When shorting the base with the emitter and collector, respectively, compared with a floating base configuration, a smaller depletion region, reduced series resistance, and larger series capacitance are observed.