In a p-n junction diode, the depletion region width depends on which of the following factors?
Depletion width W = √(2εV/qNd·Na/(Nd+Na)), dependent on applied voltage and doping concentrations.
Which of the following devices has the fastest switching speed?
MOSFETs have fastest switching due to voltage-controlled operation without minority carrier storage effects.
In an n-channel enhancement mode MOSFET, the threshold voltage (VT) is typically:
N-channel enhancement mode MOSFETs require positive gate voltage to create inversion layer for conduction.
A PIN diode is primarily used in high-frequency applications because:
PIN diodes have wide intrinsic region that reduces capacitance while increasing carrier transit time, ideal for RF switching.
In a BJT operating in the active region, which relationship holds true?
Active region requires base-emitter junction forward biased (~0.7V) and collector-base reverse biased (VCE > saturation voltage).
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The transconductance (gm) of a MOSFET in saturation region is given by:
Transconductance gm = ∂ID/∂VGS = ID/(VGS - VT) at saturation, fundamental small-signal parameter.
Which of the following statements about Zener diodes is correct?
Zener diodes operate in reverse breakdown region maintaining nearly constant voltage for voltage regulation applications.
In a CMOS inverter, the power dissipation is primarily due to:
CMOS dynamic power = CV²f dominates; ideal CMOS has zero static power as pull-up and pull-down never conduct simultaneously.
The punch-through effect in a BJT occurs when:
Punch-through occurs when CBJ depletion width extends to base contact, causing base resistance to vanish and uncontrolled current flow.
A light-emitting diode (LED) emits light when:
Forward bias injects minority carriers; their recombination releases energy as photons (electroluminescence) in direct bandgap semiconductors.
The body effect in MOSFETs causes which of the following?
Body effect (substrate bias) increases VT due to back-bias effect and decreases output impedance; VT = VT0 + √(2εqNa/Cox)·φt term.
In a Gunn diode, negative resistance occurs due to:
Gunn effect: electrons transfer from high-mobility Γ valley to low-mobility L valley at threshold field, causing dI/dV < 0 (negative resistance).
The gain-bandwidth product (GBP) of a BJT is approximately equal to:
GBW ≈ fT; BJT current gain drops with frequency as β·f ≈ constant, where fT is extrapolated cutoff frequency (~1GHz for silicon BJTs).
Channel length modulation in MOSFETs causes:
CLM: as VDS increases, pinch-off point moves toward source, reducing effective channel length; output resistance Rds = VA/ID = λ⁻¹.
In a photodiode, the photocurrent is proportional to:
Photodiode: Iph = η·q·Φ where η is quantum efficiency and Φ is incident photon flux; reverse bias increases depletion width for carrier collection.
The Miller effect in a common-emitter BJT amplifier causes:
Miller effect: CBE capacitance reflected to input = CμC·(1+|Av|); dominates high-frequency response and limits bandwidth in CE configuration.
Which semiconductor material has the lowest bandgap at room temperature?
Germanium has Eg ≈ 0.66 eV at 300K, lowest among common semiconductors; causes high intrinsic carrier concentration and leakage current.
In a thyristor (SCR), the holding current (IH) is important because:
Holding current IH: minimum anode current to sustain regenerative action (latching); if IA < IH, device reverts to blocking state.
The avalanche breakdown voltage (BV) in a reverse-biased junction approximately follows:
Breakdown voltage BV ∝ ND^(-43) approximately; lower doping increases depletion width, requiring higher field and higher voltage for breakdown.
In a p-n junction diode, the depletion width increases when:
Reverse bias widens the depletion region by pulling majority carriers away from the junction, increasing the width of the space charge region.
