Generate GATE-level questions on PN Junction and Special Diodes. Focus on:
1. P-N junction characteristics: Diode current equation and Junction capacitance.
2. Special Diodes: Zener diode, Tunnel diode, LED, Photo diode, and Solar cell.
3. Breakdown mechanisms: Zener and Avalanche breakdown.
56 questions · 20 PYQs · 0 AI practice · GATE ECE 2027
🎯 These are sample questions
Get the full Pn Junction And Special Diodes experience — 100% free
✓ Attempt tracking & analytics
✓ Timer & exam-mode simulation
✓ Adaptive difficulty (Easy → Hard)
✓ Bookmarks, notes & mistake review
Just sign in to unlock everything. Free for all students.
An ideal p-n junction germanium diode has a reverse saturation current of 10μA at 300 K . The voltage (in Volts, rounded off to two decimal places) to be applied across the junction to get a forward bias current of 100 mA at 300 K is __________ . (Consider the Boltzmann constant kB=1.38×10−23J/K and the charge of an electron e=1.6×10−19C .)
I=Is(ekBTeV−1) Where: I=100mA=0.1AIs=10μA=10×10−6AT=300Ke=1.6×10−19CkB=1.38×10−23J/K Approximate since I≫Is , so: I≈IsekBTeV Taking natural logarithm on both sides: kBTeV=ln(IsI)V=ekBTln(IsI) Now plug in the values: ekBT=1.6×10−191.38×10−23×300=0.025875Vln(10×10−60.1)=ln(10000)=ln(104)=4ln(10)≈4×2.3026=9.2104 So, V=0.025875×9.2104≈0.2382V
Q2GATE 2024NAT
The photocurrent of a PN junction diode solar cell is 1mA . The voltage corresponding to its maximum power point is 0.3V . If the thermal voltage is 30mV , the reverse saturation current of the diode (in nA , rounded off to two decimal places) is ________
A p-type semiconductor with zero electric field is under illumination (low level injection) in steady state condition. Excess minority carrier density is zero at x=±2ln , where ln=10−4cm is the diffusion length of electrons. Assume electronic charge, q=−1.6×10−19C . The profiles of photo-generation rate of carriers and the recombination rate of excess minority carriers (R) are shown. Under these conditions, the magnitude of the current density due to the photo-generated electrons at x=+2ln is _________ mA/cm2 (rounded off to two decimal places).
Continuity equation is given by Dn∂x2∂2δn+G−R...(ii) G and R both are zero - for [ln≤x≤2ln] Hence Equation (i) reduced to Dn∂x2∂nδn=0⇒δn(x)=Ax+B For calculating A and B we use Boundary condition δn(2ln)=0⇒A=2ln−B∴δn(x)=2ln−Bx+B=B[1−2lnx]...(iii) At x=ln
for ln≤x≤2ln Electron diffusion current density is given by ∣Jn∣diff=qDndxdη=qDn×2×1020×e−1×τn[0−2ln1]=2ln1.6×10−19×ln2×2×1020×e−1=1.6×10−19×ln×1020×e−1=1.6×10×1×10−4×e−1=0.59mA/cm2
Q4GATE 2021NAT
A silicon P-N junction is shown in the figure. The doping in the P region is 5×1016cm−3 and doping in the N region is 10×1016cm−3 . The parameters given are Built-in voltage (Φbi)=0.8V Electron charge (q)=1.6×10−19C Vacuum permittivity (ε0)=8.85×10−12F/m Relative permittivity of silicon (εSi)=12 he magnitude of reverse bias voltage that would completely deplete one of the two regions (P or N) prior to the other (rounded off to one decimal place) is _________V.
Given: NA=5×1016cm−3;ND=10×1016cm−3 Built-in potential, ϕbi=0.8V Electron charge, q=1.6×10−19C Vacuum permittivity, ϵo=8.85×10−12F/m=8.85×10−14F/cm Relative permittivity silicon, ϵsi=12⇒ Doping on both sides is comparable, so smaller region would deplete first. So, depletion region width on N -side =xn=0.2μm
Consider the recombination process via bulk traps in a forward biased pn homojunction diode. The maximum recombination rate is Umax . If the electron and the hole capture cross-section are equal, which one of the following is False?
A pn junction solar cell of area 1.0 cm2 , illuminated uniformly with 100 mW cm−2 , has the following parameters: Efficiency = 15%, open circuit voltage = 0.7 V, fill factor = 0.8, and thickness = 200 μm , The charge of an electron is 1.6×10−19 C. The average optical generation rate (in cm−3s−1 ) is
η0.15ISCGL=P∈(FF)VOCISC=100mW0.8×0.7×ISC=0.5615mA=q× Area × thickness ISC=0.56×1.6×10−19×1×200×10−415×10−3=0.56×3215×1019=0.837×1019
Q7GATE 2020MCQ
A one-sided abrupt pn junction diode has a depletion capacitance CD of 50 pF at a reverse bias of 0.2 V. The plot of 1/CD2 versus the applied voltage V for this diode is a straight line as shown in the figure below. The slope of the plot is ____ ×1020F−2V−1 .
As per GATE official answer key MTA (Marks to ALL) Depletion or transition capacitance is, CD=WAϵ For one-sided PN junction (EX:P+NJunction)W=eND2ϵVB=eND2ϵ(Vbi−V) where V is anode to cathode applied potential. ⇒CD=eND2ϵ(Vbi−V)Aϵ⇒CD21=A2ϵeND2(Vbi−V)CD21becomeszeroatV=Vbi From above graph, y=CD21=0atx1=VbiAndy2=CD21=4×1020atx2=−0.2VSlope=x2−X1y2−y1=−0.2−Vbi4×1020−0Vbi is not provided,slope cannot be found.
Q8GATE 2019NAT
In an ideal pn junction with an ideality factor of 1 at T=300 K, the magnitude of the reverse-bias voltage required to reach 75% of its reverse saturation current, rounded off to 2 decimal places, is ____mV. $[ k=1.38×10−23JK−1 , h=6.625×10−34J−s , q=1.602×10−19C ]$
A Germanium sample of dimensions 1cmx1cm is illuminated with a 20 mW, 600 nm laser light source as shown in the figure. The illuminated sample surface has a 100 nm of loss-less Silicon dioxide layer that reflects one-fourth of the incident light. From the remaining light, one-third of the power is reflected from the Silicon dioxide-Germanium interface, one-third is absorbed in the Germanium layer, and one-third is transmitted through the other side of the sample. If the absorption coefficient of Germanium at 600 nm is 3×104cm−1 and the bandgap is 0.66 eV, the thickness of the Germanium layer, rounded off to 3 decimal places, is ______ μm .
A junction is made between p−Si with doping density NA1=1015cm−3 and pSi with doping density NA2=1017cm−3 . Given: Boltzmann constant k=1.38×10−23JK−1 , electronic charge q=1.6×10−19C . Assume 100% acceptor ionization. At room temperature (T = 300K), the magnitude of the built-in potential (in volts, correct to two decimal places) across this junction will be _________________.
⟶ Hole diffusion ⟵ Electron diffusion ⟵ Hole drift ⟶ Electron drift ⟶ Hole diffusion current ⟶ Electron diffusion current ⟵ Hole drift current ⟵ Electron drift current
Q14GATE 2018NAT
A solar cell of area 1.0 cm2 , operating at 1.0 sun intensity, has a short circuit current of 20 mA, and an open circuit voltage of 0.65 V. Assuming room temperature operation and thermal equivalent voltage of 26mV, the open circuit voltage (in volts, correct to two decimal places) at 0.2 sun intensity is _______.
A p-n step junction diode with a contact potential of 0.65V has a depletion width of 1 μ m at equilibrium. The forward voltage (in volts, correct to two decimal places) at which this width reduces to 0.6 μ m is _______.
Red (R), Green (G) and Blue (B) Light Emitting Diodes (LEDs) were fabricated using p-n junctions of three different inorganic semiconductors having different band-gaps. The builtin voltages of red, green and blue diodes are VR,VGandVB , respectively. Assume donor and acceptor doping to be the same (NAandND , respectively) in the p and n sides of all the three diodes. Which one of the following relationships about the built-in voltages is TRUE?
λR>λG>λB Energy gap, Eg∝λ1 So, EgR<EgG<EgB Materials with high energy gap will have high built-in voltages, when doping concentrations are same. So, VR<VG<VB
Q17GATE 2017NAT
As shown, two Silicon (Si) abrupt p-n junction diodes are fabricated with uniform donor doping concentration of ND1=1014cm−3 and ND2=1016cm−3 in the n-regions of the diodes, and uniform acceptor doping concentration of NA1=1014cm−3 and NA2=1016cm−3 in the pregions of the diodes, respectively. Assuming that the reverse bias voltage is >> built-in potentials of the diodes, the ratio C1C2 of their reverse bias capacitances for the same applied reverse bias, is __________.
An n+−n Silicon device is fabricated with uniform and non-degenerate donor doping concentrations of ND1=1×1018cm−3 and ND2=1×1015cm−3 corresponding to the n+ and n regions respectively. At the operational temperature T, assume complete impurity ionization, kT/q = 25 mV, and intrinsic carrier concentration to be ni=1×1010cm−3 . What is the magnitude of the built-in potential of this device?
For a particular intensity of incident light on a silicon pn junction solar cell, the photocurrent density ( JL ) is 2.5 mA/ cm2 and the open-circuit voltage ( Voc ) is 0.451 V. consider thermal voltage ( VT ) to be 25mV. If the intensity of the incident light is increased by 20 times,assuming that the temperature remains unchanged. Voc (in volts) will be ______.
An abrupt pn junction (located at x = 0) is uniformly doped on both p and n sides. The width of the depletion region is W and the electric field variation in the x-direction is E(x). Which of the following figures represents the electric field profile near the pn junction?
