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Correct OPTION is (a) less than that of a GENERAL PN diode

The best explanation: The current flow of the point CONTACT diode is not independent of voltage applied to the crystal unlikely to a general PN diode. This characteristic of contact diode makes its capacitance high at high frequency. A small capacitive current flows in the circuit.

The correct option is (d) REACTANCE increases

Explanation: In a low FREQUENCY model, the resistance DECREASES and reactance increases.Here the VARIABLE resistance is neglected. At low frequencies, the charge can be REMOVED and the diode can be turned off.

Right option is (C) for heat dissipation and REDUCE induction respectively

The BEST explanation: Anode goes through better heat dissipation. So the pellet is used for the purpose. The TINDOT via mesh screen resists INDUCTIVE effects caused at the cathode. Conduction is an independent factor which can’t be controlled.

Correct OPTION is (a) 23.7mA

The explanation: Here, I1MAX=IZMIN+ILMAX.

IZMIN =0.5mA, I1MAX =(V1MAX-VZ )/RS . PUTTING the values we get , I1MAX =24.2mA.

So, 24.2-0.5=23.7mA.

Correct option is (a) 0.1pF to 1pF

The best I can explain: The barrier capacitance at the point is very LOW about 0.1pF to 1pF. The capacitance between the cat WHISKER and crystal is less compared to junction diode capacitance between both SIDES of the diode. For a general PN diode is 0.008µF to 20µF.

The correct option is (b) RF = W/σN

For EXPLANATION: Forward resistance for a PIN diode depends on the width, current density and positive carrier CONCENTRATION of the diode. No diode is perfectly ideal. In practise, a diode OFFERS a small resistance in forward bias which is CALLED as forward resistance.

Correct OPTION is (a) 0.1 to 10KΩ and 0.02 to 2PF RESPECTIVELY

For explanation I would say: At high frequency, the applied VALUES for resistance and capacitance is 0.1 to 10KΩ and 0.02 to 2pF respectively. At high frequencies, it almost acts as a perfect RESISTOR.

The correct option is (d) AM detectors

To EXPLAIN: The POINT contact diodes are the oldest MICROWAVE semiconductor devices. They were developed duringworld war 2. They have excessive applications in microwave fields and USED as RECEIVERS and detectors.

The correct choice is (a) a variable resistor

The best EXPLANATION: In forward bias, the forward resistance decreases and acts as a variable resistor. The LOW FREQUENCY model of a PIN diode NEGLECTS the INPUT capacitive values.

Correct answer is (a) it behaves as a normal diode

For explanation: After the valley point is crossed,the TUNNEL diode obtains positive SLOPE resistance. That is SIMILAR to the CHARACTERISTICS of a normal diode. So it behaves like a normal diode after beyond valley point.

Correct option is (a) p ∝ e^(-A*e*w)

To elaborate: The carrier jump occurs WITHOUT any loss of energy due to small depletion layer. The probability of the carrier to jump across a barrier DEPENDS on the energy and WIDTH of the band. This variess EXPONENTIALLY for a given carrier.

The correct answer is (b) depletion layer increases GIVING a larger surface AREA

The best I can EXPLAIN: An intrinsic layer that is sandwiched between p and n layers. This GIVES a larger surface area making it compatible for photosensitivity. Reverse bias causes an increased depleted region in a PIN diode.

The correct choice is (a) its abrupt and has high dopants

Easy explanation: When the P and N regions are very highly doped, the depletion layer comes closer. The TUNNEL diode is also highly doped. Its doping concentration VARIES within a small scale. So it’s an abrupt diode. For these reasons, the depletion region is small.

The correct choice is (d) X operates in FORWARD bias and Y operates in reverse bias

To explain I would say: In forward bias, negative resistance helps for TUNNEL DIODE to operate. Here, the CURRENT decreases with increase in voltage. If they are used in reverse bias, they are called as back diodes. Avalanche diode operates in reverse bias at breakdown region.

The correct option is (c) microwave FREQUENCY region

The explanation: Tunnel DIODE is a type of semiconductor which works on TUNNELING effect of ELECTRONS in microwave region. So, tunnel diode has a very FAST operation in microwave region.

Right option is (B) to form small REGION of p type material

Easiest explanation: The behaviour of a contact diode is similar to that of a PN diode. It has a TUNGSTEN wire which is called as a cat whisker wire. This helps in pressing ONE SECTION to other.

The correct option is (c) 7.5V,-0.7V

The explanation is: With VI= 10V when MAXIMUM, D1 is FORWARD biased, D2 is reverse biased. ZENER is in breakdown REGION. VOMAX=sum of breakdown voltage and diodedrop=6.8+0.7=7.5V. VOMIN=negative of voltage drop=-0.7V. There will be no breakdown voltage here.

Right option is (a) lower

Explanation: The current flow of the POINT CONTACT diode is not INDEPENDENT of VOLTAGE APPLIED to the crystal unlikely to a general PN diode. A small capacitive current flows in the circuit.

Right option is (B) SnTe or BI2TE3

Explanation: The DIODE base of SnTe or Bi2Te3 is highly detection sensitive. They are mechanically stable over long periods of USE either as harmonic generators or mixers. They are emphasized in the 2-200THz REGION.

Right option is (a) IF = A(µPP + µNN)q

Explanation: The forward CURRENT depends on mobility and carrier concentration. In frequency models, the value of forward current is IF = A*(µPP + µNN)q. Where, µP and µN are the mobility of p and n TYPE charge CARRIERS respectively.

The correct option is (a) it’s photosensitive in reverse bias

The EXPLANATION: Due to increased depletion region, the covalent BONDS break and increase the surface area for photosensitivity. This PROPERTY is used in fields of light sensors, image SCANNERS, artificial retina systems.

The correct OPTION is (c) MAINTAINING the pressure between sections

For explanation: The OPERATION of a contact diode depends on the pressure of contact between semiconductor CRYSTAL and point. The cat whisker wire presses against the crystal to form a section and the section allows the current flow. This is similar to the behaviour of PN diode.

The correct choice is (a) ELECTRIC current multiplication takes place

The explanation is: The carriers in TRANSITION region are accelerated by electric field to ENERGIES. That energies are sufficient to CREATE electron current multiplication. A single carrier that is energized will collide with another by gaining energy. Thus an avalanche multiplication takes place.

The CORRECT option is (d) π and ϒ regions

Easy EXPLANATION: When P region is used for HIGH resistance, the depletion layer is high at p side.When n side is used the depletion layer is high at n side. They are CALLED as π and ϒ regions respectively.

The correct answer is (a) GERMANIUM and silicon materials

To EXPLAIN: Germanium and silicon materials have low band gaps and flexibility. That matches tunnel DIODE requirements. The remaining materials EMITS the energy in terms of light or heat.

Right option is (c) VARIABLE capacitor

To explain: In reverse BIAS, the intrinsic layer is completely covered by depletion layer. Thestored charges vanishes acting LIKE a variable capacitor. The high frequency model of a PIN diode neglects the input RESISTANCES.

Correct choice is (a) electrons move frombalance band of pside to conduction band of nside

For explanation I would say: When the forward bias is increased, the tunnel CURRENT is also increased upto a certain limit. This happens when the ELECTRON movement TAKES place from P to N side.

Right answer is (a) to have low BREAKDOWN voltage

Easiest explanation: The VALUE of reverse breakdown voltage at which zener breakdown occurs is CONTROLLED by amount of DOPING. If the amount of doping is high, the value of voltage at which breakdown occurs will decrease. BETTER doping gives a sooner breakdown voltage.

The correct CHOICE is (B) 80 Ω

Explanation: Here, VZ =6V, IZMIN=5mA.IS=IZMIN+ILMAX.

80=5+ILMAX . ILMAX=75Ma.RLMIN=VI/ILMAX=6/75mA

=80 Ω.

The correct option is (b) temperature increases and crystal IONS VIBRATE with LARGE amplitudes

The best explanation: When voltage is INCREASED, the tunnelling at reverse bias increases. The voltage RISES temperature. The crystal ions with greater thermal energy tend to vibrate with larger amplitudes.

Correct choice is (b) movement of electrons from n side conduction band to p side VALANCE band

To elaborate: Tunneling MEANS a DIRECT flow of electrons across small depletion region from N side conduction band to P side valance band. The electrons BEGIN to ACCELERATE in the N side of the semiconductor.

The CORRECT OPTION is (B) -200V/m

The EXPLANATION is: Emax=-2(Vbi+VR)/W

=-2(2+5)/ (7*10^-2)

=-200V/m.

The correct option is (C) -2mA

The best explanation: INITIALLY, the diode is in forward bias. When suddenly SWITCHED to reverse bias, upto a storage TIME limit, it CONDUCTS during storage time period.

We know that, current I=V/R=-20/10K=-2mA.

Right choice is (d) 0A

Easy explanation: If there is any CURRENT present under OPEN CIRCUIT there will be an indefinite growth of holes at ONE end of the semiconductor which is practically not possible hence zero AMPERES.

The correct CHOICE is (d) 0.25 m^2/ (vs)

The explanation: We KNOW that MOBILITY of charge carriers is drift velocity DIVIDE by applied electric field INTENSITY. Mobility = drift velocity / field intensity.

Correct choice is (b) UNCOVERED charges

Explanation: The un-neutralised IONS in the NEIGHBOURHOOD of the JUNCTION are known as uncovered ions because they are not mobile.

Correct option is (d) Life time of MINORITY CARRIERS in N junction

For explanation: Switching leads to move HOLES in P region to N region as minority carriers. REMOVAL of this accumulation DETERMINES switching speed. P+ regards to a diode in which the p type is doped excessively.

Right option is (a) Time taken to eliminate excess minority CHARGE carriers

Best explanation: The time PERIOD for which diode remains in conduction state even in REVERSE direction is called storage time. The time ELAPSED to return the non conduction state is called transition time. Their sum is called reverse RECOVERY time.

Correct answer is (c) Diffusion current

For EXPLANATION I WOULD SAY: In a semiconductor the CHARGE will always have a tendency to move from higher concentrated area to less concentrated area to maintain equilibrium this movement of charges will result in diffusion current.

The correct OPTION is (C) 0eV

The best I can explain: Eo=kTln((Nd*Na)/(ni)^2)

Substituting k=1.38*10^-23/K, T=300k and the VALUES ofNd,NAAND ni,

We get

Eo=0eV.

Correct choice is (b) V= V0

To explain I WOULD SAY: When the voltage will be same that of the POTENTIAL BARRIER, the potential barrier disappears resulting in flow of current.

The CORRECT OPTION is (b) Left

To explain: The p-type carriers are NOMINALLY located to the left of the JUNCTION and n-type carriers are to the right.

The correct OPTION is (C) 10µF/m^2

Explanation: We know, CT =Aε0εr /W

CT/A= (8.85×10^-12)(11.7)/10

=10

 By PUTTING the VALUES we get 10µF/m^2.

Correct CHOICE is (a) tunneling of charge carriers across the junction

The best I can EXPLAIN: Due to zener EFFECT in reverse BIAS under high electric field strength, electron quantum tunneling occurs. It’s a mechanical effect in which a tunneling current occurs through a barrier. They usually cannot move through that barrier.