Semiconductor Devices and Electronics Flashcards

The channel length modulation parameter λ in a MOSFET affects which characteristic?

Answer: The slope of ID vs. VDS in the saturation region

Channel length modulation (λ) causes a slight increase in drain current with VDS in saturation, giving ID a finite slope rather than being flat.

In a common-base BJT amplifier, the current gain (α) is always:

Answer: Less than 1 but close to 1

Alpha α = IC/IE < 1 because IE = IC + IB and some base current is lost, but α is typically 0.95–0.999.

A Schottky diode differs from a standard p-n junction diode primarily because it:

Answer: Uses a metal-semiconductor junction and has faster switching with lower forward voltage

Schottky diodes form metal-semiconductor junctions, resulting in majority-carrier conduction, ~0.3 V forward drop, and very fast switching.

The substrate bias effect (body effect) in a MOSFET causes the threshold voltage to:

Answer: Increase as substrate reverse bias increases

Increased reverse substrate bias widens the depletion region, requiring more gate voltage to invert the channel, raising VT.

Which configuration of an op-amp has the highest input impedance and unity voltage gain?

Answer: Voltage follower (unity-gain buffer)

The voltage follower connects the output directly to the inverting input, achieving unity gain with ideally infinite input impedance.

In a semiconductor, the Fermi level in an intrinsic material lies:

Answer: Near the middle of the bandgap

In an intrinsic semiconductor, the Fermi level (intrinsic level Ei) lies approximately at the midgap due to equal electron and hole concentrations.

The diffusion capacitance of a forward-biased p-n junction is due to:

Answer: Minority carrier charge stored in the quasi-neutral regions

Diffusion capacitance arises from excess minority carriers injected and stored in the bulk regions adjacent to the junction under forward bias.