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Semiconductor Devices 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.

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  1. In a MOSFET, the gate terminal is insulated from the channel by which material?

    Answer: Silicon dioxide (SiO2)

    The MOSFET gate is separated from the channel by a thin silicon dioxide (SiO2) insulating layer, which is why virtually no gate current flows.

  2. A BJT is said to be in saturation when:

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

    Saturation occurs when both junctions are forward biased, causing VCE to drop to a low value (typically 0.2 V for silicon) and the transistor acts like a closed switch.

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

    Answer: Very high current gain (β² ≈ β1 × β2)

    A Darlington pair cascades two BJTs so their betas multiply, yielding an extremely high overall current gain equal to approximately β1 × β2.

  4. Which type of diode is specifically designed to emit light when forward biased?

    Answer: Light-emitting diode (LED)

    LEDs are made from direct-bandgap semiconductors (like GaAs or GaN) where electron-hole recombination releases energy as photons rather than heat.

  5. The Early effect in a BJT refers to:

    Answer: Narrowing of the base width as VCE increases, causing IC to rise slightly

    The Early effect (base-width modulation) occurs when higher VCE widens the collector depletion region, effectively narrowing the base and slightly increasing IC.

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

    Answer: Off, and requires a positive VGS above the threshold voltage to create a channel

    Enhancement-mode MOSFETs have no conducting channel at VGS = 0 and require VGS to exceed the positive threshold voltage (VT) to induce a channel.

  7. A varactor (varicap) diode is used primarily as a:

    Answer: Voltage-controlled capacitor

    A varactor diode exploits the voltage-dependent capacitance of its reverse-biased depletion region, making it useful as a voltage-controlled capacitor in tuning circuits.