Govt. Exams
At thermal equilibrium, the built-in electric field points from the p-region (positive) to n-region (negative) to oppose further diffusion of carriers.
At pinch-off voltage, the depletion region extends completely across the channel width, cutting off the flow of carriers and reducing drain current to nearly zero (IDSS becomes zero).
The bandgap energy decreases with increasing temperature at a rate of approximately -2 to -4 meV/K, described by the Varshni equation: Eg(T) = Eg(0) - αT²/(T+β)
Adding donor atoms to a p-type semiconductor introduces electrons, shifting the material towards n-type behavior and moving the Fermi level toward the conduction band.
In an intrinsic semiconductor, the number of electrons equals the number of holes as they are generated in pairs. Both equal the intrinsic carrier concentration ni.
In LEDs (forward biased p-n junctions in direct bandgap semiconductors like GaAs), electron-hole recombination releases energy as photons. Indirect bandgap materials (Si, Ge) produce mainly heat.
Boron is a Group III element (trivalent) that acts as an acceptor in silicon, creating holes and forming p-type semiconductor. Phosphorus, Arsenic, and Antimony are Group V elements (pentavalent) forming n-type semiconductors.
Silicon has a bandgap of approximately 1.1 eV at 300 K. This is a standard value used in semiconductor physics and device design.
At T = 0 K, all electrons remain in the valence band. No thermal energy is available to excite electrons to the conduction band, so free electrons are zero.
GaAs is a direct bandgap semiconductor where the minimum energy gap occurs at the same k-value, making it suitable for light emission. Si and Ge are indirect bandgap semiconductors.
