Assertion (A) : A tunnel diode consists of simple p-n junction mode of degenerate semiconductor. The current voltage characteristics consists of three components and shows the negative differential region over part of the forward characteristics. Reason (R) : In tunnel diode the p-side is highly doped and n-side is highly doped and also used as detector.
(A) is correct but (R) is not correct
The assertion is a correct description; the reason spoils an otherwise true statement by adding a false application — option 3.
The assertion, checked in three parts.
Degenerate p-n junction. Both sides are doped to \(10^{19}\)–\(10^{20}\ \text{cm}^{-3}\), so heavily that the Fermi level moves into the bands themselves. The depletion layer shrinks to about 10 nm — thin enough for carriers to tunnel straight through it.
Three current components. The characteristic is genuinely a sum of three terms, and this is the detail the assertion gets right:
| Component | Where it dominates |
|---|---|
| Band-to-band tunnelling current | Small forward bias, up to the peak |
| Excess current (via band-gap states) | The valley region |
| Normal thermal diffusion current | Beyond the valley |
Negative differential resistance over part of the forward characteristic. Between the peak and the valley, the occupied states on one side cease to line up with empty states on the other, the tunnelling window closes, and current falls as voltage rises. It is over part of the forward range only, exactly as stated.
Where the reason goes wrong. Its first half is correct — both sides are heavily doped, and that is the essential condition. But it then adds "and also used as detector", which is not a property of the tunnel diode. Its uses follow from the negative resistance: microwave oscillators and amplifiers, and very fast switching. Detection requires a strongly rectifying, asymmetric characteristic, and the tunnel diode has the opposite — it conducts readily in both directions at small bias, since reverse bias only widens the tunnelling window. That is precisely why the backward diode, a tunnel diode doped just short of showing a peak, is the member of the family used for detection.
A note on the logic. Even had the reason been wholly true, it would not have explained the assertion: heavy doping accounts for the tunnelling and hence for the negative-resistance region, but a statement about applications explains nothing about the shape of a characteristic. The added clause makes the question simpler, since a reason containing a false element is false as a whole.
Hence, (A) is correct but (R) is not correct.
Similar Questions
A PIN diode can not be used as
i. Microwave switch
ii. Microwave mixer
iii. Microwave detectorWhich is correct ?
________ diode is not used as a microwave mixer or detector.
Match the given lists :
List – I (Name of the Device) List – II (Application) a. Diode i. Rectification b. Tunnel diode ii. Microwave switching c. Zener diode iii. An oscillator d. PIN diode iv. Voltage regulation Codes :
An important figure of merit for microwave application of Schottky diode is forward bias cut off frequency fco and is given by :
Varacter diodes have the following properties :
A. Junction capacitance varies with bias voltage
B. Junction capacitance varies with time
C. Non linearity of varacter diodes makes them suitable for frequency multipliers
D. Linearity of varactor diode makes them suitable for frequency multipliers.
Choose the correct answer from the options given below:
In a tunnel diode, the degeneracy on the n-side can be expressed as
The static current voltage characteristics of a tunnel diode consist of
(a) Tunneling current and thermal current
(b) Thermal current and excess current
(c) Tunneling current only
(d) Tunneling current, excess current and thermal current
Out of these which are correct ?
Match the following :
List – I List – II a. Gunn diode i. degenerate silicon b. Tunnel diode ii. n-type Ga As c. BJT iii. Silicon d. Diode (P-N junction) iv. \(I_o\left[\exp\left(\dfrac{qV}{kT}\right)-1\right]\) Choose the correct answer from the codes given below:
A TRAPATT diode has the doping concentration NA = 2 x 1015/cm3 and a current density of 20 kA/cm2. The value of avalanche zone velocity is given by :
Assertion (A) : The Gunn diode characteristics shows the region of negative resistance.
Reason (R) : The Gunn diode is made of n-type and p-type degenerate semiconductor.
Select your answer using the codes given below.
Important Questions from Types of Diode
For which of the following diodes when the voltage is increased the current flowing through it decreases?
Which of the following is the main application of Zener diode?
A tunnel diode is
When we tune in any desired station in a radio receiver by rotating the tuning control we vary
Which diode is used as a voltage regulator?
