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Operation of a SEBAT. (a) Circuit schematic of a -type SEBAT associated with a passive quenching circuit. The symbol of the SEBAT is similar to that of a conventional bipolar transistor. The notations are E, emitter; B, base; C, collector; , inherent capacitance of the collector-base junction, , quenching resistor; , supply voltage; , emitter (input) current; , avalanche current; recharging current; and , collector-base voltage. (b) Collector-base voltage as a function of time. Whenever an electron triggers the avalanche current , drops from to the breakdown voltage . The width of the voltage pulses is determined by the recharging time constant . The average pulse rate, , is proportional to the ideal input current . (c) The output voltage of the inverter as a function of time. and are the supply voltages of the inverter, and is its threshold voltage.
(a) Photomicrograph of the circuit, comprising the bipolar transistor (BT), the quenching resistor , and the integrated inverter (INV). (b) Schematic cross section of the bipolar transistor optimized for Geiger-mode operation. Notations: E, emitter; B base; C, collector; S, substrate; , base contact; , collector contact; and GR, guard ring.
(a) Output voltage as a function of time at a mean avalanche firing rate of about , corresponding to . (b) for , which corresponds to . (c) Detail of (b) showing typical pulses in . (d) and recorded simultaneously as functions of at ambient temperature . The count rate scale is linked to the current scale through the relationship . Therefore, it is possible to compare visually expressed as an electron count rate to the measured output pulse rate. Also shown are for and, as a black line, the theoretical value of for , with the coefficient as the only fitting parameter.
Average output pulse rate after subtraction of the parasitic count rate and emitter current as a function of the base-emitter voltage at three different temperatures. is evaluated by measuring for . The values of are about at , at , and at . A least squares exponential fit of is shown as a continuous line.
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