Govt. Exams
Entrance Exams
Silicon has dominated modern rectifiers because of significantly lower reverse saturation current (leakage ~nA at room temperature vs ~µA for Ge), better temperature stability, and superior thermal properties. The extra 0.4V drop is offset by reduced losses in high-power applications.
The current gain β is the ratio of collector current to base current (I_c/I_b). For silicon transistors, typical β values range from 50 to 500.
Reverse bias strengthens the electric field across the junction, causing the depletion region to expand as more charge carriers are pulled away from the junction.
P-type semiconductors are doped with acceptor impurities which create holes as majority carriers. Electrons become minority carriers in p-type material.
Germanium has a bandgap of approximately 0.66 eV at room temperature (300K), making it a narrow bandgap semiconductor compared to silicon (1.1 eV).
In an intrinsic semiconductor, every electron-hole pair is generated together, so the concentration of free electrons equals the concentration of holes, both equal to the intrinsic carrier concentration n_i.
The built-in potential (V₀) develops naturally across a p-n junction due to diffusion of charge carriers. For silicon at 300 K, V₀ ≈ 0.7 V, independent of external voltage.
The intrinsic carrier concentration (ni) of silicon at 300 K is approximately 1.5 × 10^10 cm^-3, which is a standard value used in semiconductor calculations.
Photoconductivity is the increase in conductivity when photons with E > Eg create electron-hole pairs, increasing charge carrier concentration.
In active mode, BE junction is forward biased (injects carriers) while BC junction is reverse biased (collects carriers).
