My name is nassim aliouche, I am a final year student in microtechnology at Marne la Vallée University , i am working on a presentation about the bipolar Transistor SiGe
So , for For SiGe HBTs what physical phenomenon do we observe in terms of band diagram at low temperature (cryogenic), at very low-temperature millikelvin, and at high temperature?
Dear Nassim,
I already characterized SiGe HBTs from ASIC technology down to cryogenic temperatures (about 2K) ... but not down to sub-kelvin. Overall, the current gain of SiGe HBT and the transconductance (gm=qI/kT) increase at low temperatures. Vbe is also increasing with cooling, going from about 0.7V at room temperature to larger than 1V at cryogenic temperatures. But, below few 10K, many phenomena (silicon freezeout, thermal sensitivity, g-r noise, non-ideality, self heating, Vce threshold, hysteresis ...) counteract these tendances.
Moreover, the interpretation of the temperature itself stated to be confused below few Kelvins. Indeed, thermal-interface (conductance), electron/phonon decoupling and self-heating lead to the existence of an "effective temperature" of any junctions, warmed at a higher temperature than the sub-kelvin bath.
best wishes
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