Govt. Exams
Diffusion length Ln = √(Dn·τn) where Dn is diffusion coefficient and τn is minority carrier lifetime. It represents the average distance a carrier travels before recombination.
Direct bandgap semiconductors like GaAs allow radiative recombination (photon emission) without phonon assistance, making them ideal for LEDs and lasers.
Zener breakdown (sharp, reversible breakdown at lower voltages) occurs when a strong electric field in the depletion region enables direct tunneling of electrons across the narrow bandgap.
I₀ ∝ ni² which increases exponentially with temperature. This thermal generation of minority carriers in the neutral regions near the junction constitutes the reverse saturation current.
Using mass action law: ne·nh = ni². Since ne ≈ Nd = 10^16 cm^-3, then nh = ni²/ne = (1.5×10^10)²/10^16 = 2.25×10^4 cm^-3
Increasing reverse bias voltage creates a stronger electric field, pushing charge carriers away from the junction and widening the depletion region according to W ∝ √V.
Though mobility decreases with temperature (T^-3/2), the exponential increase in carrier concentration (proportional to exp(-Eg/2kT)) dominates, resulting in net increase in conductivity.
Photo-generated current IL is directly proportional to incident light intensity (photon flux). At open circuit, the current is independent of applied voltage; voltage dependence matters for load characteristics.
For n-type semiconductors, charge carriers are electrons (negative), so the Hall coefficient is negative. For p-type (holes), it is positive. The sign determines carrier type.
In saturation, both junctions are forward biased, allowing maximum current flow. In active region, BE is forward and CB is reverse biased. In cutoff, both are reverse biased.
