Discussion in 'Homework Help' started by Vish_Uday, Jul 17, 2008.
Why Germanium can not be used in SCR(silicon controlled rectifier) instead of Silicon ??
It could, but think in terms of power requirements.
From The controlled Rectifier, by the International Rectifier Corportation, Volume 1, 1962, p.10 . "For power devices, pure silicon is at present the most advantageous material. It is very abundant in nature, easily obtained and has good electrical and mechanical properties. Germanium is less advantageous because its maximum temperature limit is too low to justify its use as a power device. some the the limitations of silicon that preclude its use for other semiconductor devices are not of major concern in the manufacture of controlled rectifiers." Ratch
Germanium as a semiconductor material is more susceptible to the effects of thermal runaway than silicon. Therefore from a designers perspective silicon is more desirable to work with than germanium.
Semiconductor junctions made with Germanium are more 'leaky' than Silicon ones, by one to several orders of magnitude.
Germanium power diodes used to be made for welding equipment for instance. But they had a relatively high leakage.
This did not matter for straightforward rectification, or even for amplification in simple transistors.
However the SCR / Triac relies on regenerative amplification to 'latch' into the on state when a suitable small current is supplied to the gate terminal. If the device were to be made of germanium there would be so much leakage the device would be permanently triggered.