In a p-n junction diode, the depletion region width depends on which of the following factors?
A Applied voltage and doping concentrations B Temperature and light intensity only C Forward bias voltage only D Frequency of applied signal
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?
A BJT B MOSFET C IGBT D Thyristor
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:
A Negative B Zero C Positive D Frequency dependent
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:
A It has lower capacitance than regular diodes B The intrinsic region reduces junction capacitance and increases minority carrier lifetime C It operates at higher forward bias voltages D It has better thermal stability
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?
A VCE < 0.2V B VBE ≈ 0.7V and VCE > VCE(sat) C Both VCE and VBE are zero D VCE > VBE by more than 1V
Active region requires base-emitter junction forward biased (~0.7V) and collector-base reverse biased (VCE > saturation voltage).
The transconductance (gm) of a MOSFET in saturation region is given by:
A gm = μnCox(W/L)(VGS - VT)² B gm = 2μnCox(W/L)ID C gm = ID/(VGS - VT) D gm = (VGS - VT)/ID
Transconductance gm = ∂ID/∂VGS = ID/(VGS - VT) at saturation, fundamental small-signal parameter.
Which of the following statements about Zener diodes is correct?
A They operate in forward bias region for voltage regulation B They are reverse biased and maintain constant voltage across their terminals C They have no temperature coefficient of voltage D They can regulate both positive and negative voltages simultaneously
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:
A Leakage current only B Static current during logic transitions C Dynamic current during charging/discharging of load capacitance D Forward bias voltage drop
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:
A Base-emitter junction breaks down B Reverse bias on collector-base junction extends depletion region to base contact C Collector current exceeds maximum rating D Temperature exceeds junction temperature limit
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:
A Reverse biased beyond breakdown voltage B Forward biased and minority carriers recombine across the bandgap C Operated at room temperature D Connected in parallel with a resistor
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?
A Increase in transconductance B Decrease in threshold voltage C Increase in threshold voltage and decrease in output impedance D No change in device characteristics
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:
A Impact ionization breakdown B Differential mobility in different valley structures of semiconductor C Tunneling phenomenon D Avalanche multiplication
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:
A Current gain × operating frequency B Transconductance / gate capacitance C fT (transit frequency) where hFE·fβ = constant D Collector current / base-emitter voltage
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:
A Reduced saturation current B Finite output impedance Rds ≈ VA/ID C Increased threshold voltage D Zero Early voltage effect
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:
A Applied reverse bias voltage B Incident light intensity and quantum efficiency C Forward bias current D Operating temperature
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:
A Decrease in input impedance B Effective multiplication of base-collector capacitance by (1+Av) at input C Increase in voltage gain D Phase shift of 180°
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?
A Silicon (1.12 eV) B Gallium arsenide (1.42 eV) C Germanium (0.66 eV) D Silicon carbide (3.26 eV)
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:
A It determines maximum forward current B It is the minimum current required to maintain conduction after gate pulse is removed C It controls the forward voltage drop D It increases with temperature
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:
A BV ∝ ND (doping concentration) B BV ∝ √ND C BV ∝ ND^(-4 3 D BV is independent of doping concentration
Breakdown voltage BV ∝ ND^(-4 3
In a p-n junction diode, the depletion width increases when:
A Reverse bias voltage increases B Forward bias voltage increases C Temperature decreases significantly D Doping concentration increases
Reverse bias widens the depletion region by pulling majority carriers away from the junction, increasing the width of the space charge region.
