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Semiconductor Device Principles Flashcards

7 cards from real ISCET practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

Read the first 7 Semiconductor Device Principles flashcards as text

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

    Answer: L = √(D × τ)

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

  2. An NPN transistor is in saturation when:

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

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

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

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

    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.

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

    Answer: 1

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

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

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

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

  6. In the MOSFET body effect, applying a reverse body-to-source voltage (VBS < 0 for N-channel) causes VTH to:

    Answer: Increase, requiring a higher VGS to invert the channel

    A reverse body bias widens the depletion region under the channel, requiring more gate voltage to achieve inversion, thus increasing VTH.

  7. What is the primary advantage of using a Darlington transistor pair configuration?

    Answer: Very high current gain (β_total ≈ β₁ × β₂) with improved drive capability

    A Darlington pair multiplies the individual transistor beta values (β_total ≈ β₁ × β₂), providing very high current gain ideal for driving heavy loads from small input currents.