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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 diffusion capacitance of a forward-biased p-n junction proportional to?

    Answer: Forward bias current

    Diffusion capacitance is proportional to the DC forward bias current because more current means more stored minority charge.

  2. In an enhancement-mode N-channel MOSFET, the device is normally:

    Answer: OFF with zero gate bias and turned ON by positive VGS above threshold

    Enhancement-mode MOSFETs have no channel at VGS = 0 and require VGS > VTH to invert the channel and allow drain current.

  3. What is the transconductance (gm) of a MOSFET in the saturation region given ID = 4 mA and VGS – VTH = 2 V?

    Answer: 4 mA/V

    In saturation, gm = 2·ID / (VGS – VTH) = (2 × 4 mA) / 2 V = 4 mA/V.

  4. Which type of breakdown in a reverse-biased diode is dominant at voltages below approximately 5 V in heavily doped junctions?

    Answer: Zener (tunneling) breakdown

    Zener (band-to-band tunneling) breakdown dominates in heavily doped junctions at low reverse voltages (below ~5 V) where the depletion region is very narrow.

  5. The pinch-off voltage (VP) of a JFET is the value of VGS at which:

    Answer: The channel is completely depleted and drain current drops to zero

    Pinch-off voltage is the gate-to-source voltage that fully depletes the channel, cutting off drain current (IDSS approaches zero).

  6. A silicon BJT has β = 100 and IC = 5 mA. What is the approximate base current IB?

    Answer: 0.05 mA

    IB = IC / β = 5 mA / 100 = 0.05 mA (50 µA).

  7. What physical phenomenon causes the channel-length modulation effect in short-channel MOSFETs?

    Answer: Extension of the drain depletion region into the channel, reducing effective channel length

    As VDS increases beyond pinch-off, the drain depletion region expands toward the source, shortening the effective channel and increasing drain current.