ISCET Semiconductor Device Principles 5

Question 1

What is the relationship between the diffusion length (L) and minority carrier lifetime (τ) and diffusivity (D)?

Accepted Answer

L = √(D × τ)

Answer

Diffusion length L = √(Dτ), representing the average distance a minority carrier travels before recombining.

Question 2

An NPN transistor is in saturation when:

Accepted Answer

Both the emitter-base and collector-base junctions are forward biased

Answer

Saturation occurs when both junctions (E-B and C-B) are forward biased, causing VCE to drop to VCE(sat) ≈ 0.2 V.

Question 3

What causes hot-carrier degradation in short-channel MOSFETs?

Accepted Answer

High electric field near the drain accelerating carriers to energies sufficient to cause impact ionization or oxide injection

Answer

In short-channel devices, the high lateral field near the drain accelerates carriers to high energies ('hot'), causing impact ionization, substrate current, and oxide trap creation.

Question 4

The unity-gain frequency (fT) of a BJT is defined as the frequency at which the common-emitter current gain (|hFE|) equals:

Accepted Answer

1

Answer

fT is the transition frequency where the magnitude of the short-circuit common-emitter current gain falls to unity (1).

Question 5

Which doping profile produces an abrupt p-n junction as opposed to a graded junction?

Accepted Answer

Ion implantation with a step-function profile at the metallurgical junction

Answer

A step-function (abrupt) doping change at the metallurgical junction, achievable with ion implantation, defines an abrupt p-n junction.

(ISCET) International Society of Certified Electronics Technicians Practice Test

(ISCET) International Society of Certified Electronics Technicians Practice Test

ISCET Semiconductor Device Principles 5