BEE Bachelor of Electrical Engineering Semiconductor Devices and Electronics Questions and Answers Flashcards

What determines the width of the depletion region in a reverse-biased p-n junction?

Answer: Applied reverse voltage and doping concentrations

The depletion width increases with higher reverse voltage and decreases with higher doping concentrations on either side of the junction.

In a common-emitter BJT amplifier, what is the phase relationship between the input and output signals?

Answer: 180 degrees out of phase

A common-emitter amplifier inverts the signal, producing an output that is 180 degrees out of phase with the input.

What is the dominant carrier transport mechanism in the base region of a BJT operating in the active mode?

Answer: Diffusion

In the narrow base region of a BJT, minority carriers injected from the emitter travel primarily by diffusion due to the concentration gradient.

Which parameter of a MOSFET is defined as the ratio of change in drain current to change in gate-source voltage?

Answer: Transconductance (gm)

Transconductance (gm) measures how effectively the gate voltage controls the drain current and is defined as ∂ID/∂VGS.

What type of recombination dominates in indirect bandgap semiconductors like silicon?

Answer: Shockley-Read-Hall recombination via trap states

In indirect bandgap semiconductors, direct radiative recombination is unlikely, so recombination occurs primarily through trap states in the bandgap via the Shockley-Read-Hall mechanism.

What happens to the drain current of an enhancement-mode NMOS transistor when VGS is below the threshold voltage?

Answer: The transistor is in cutoff with essentially zero drain current

When VGS is below Vth in an enhancement-mode NMOS, no inversion channel forms and the transistor remains in cutoff with negligible drain current.