Which of the following statements are correct for Tunnel Diode ? (a) 1 impurity atom in 103 atoms (b) Very high doping in both p and n regions (c) 1 impurity atom in 108 atoms (d) used as a voltage controlled devices Out of the above, the following is the correct answer :
(a) and (b) are correct
Statements (a) and (c) contradict each other, so exactly one can be right — and settling which is the fastest route to the answer.
Work out what each doping level means numerically. Silicon contains about \(5\times10^{22}\) atoms/cm3.
| Statement | Impurity fraction | Doping density | Regime |
|---|---|---|---|
| (a) | 1 in 103 | \(5\times10^{19}\ \text{cm}^{-3}\) | Degenerate — tunnel diode ✓ |
| (c) | 1 in 108 | \(5\times10^{14}\ \text{cm}^{-3}\) | Ordinary lightly doped diode ✗ |
A tunnel diode needs doping of order \(10^{19}-10^{20}\ \text{cm}^{-3}\), so (a) is correct and (c) is wrong. That immediately removes options 2, 3 and 4, all of which include (c) — leaving option 1 as the only possibility.
Statement (b) — correct, and it is the essential point. Both sides must be degenerately doped, so that EF lies inside the conduction band on the n-side and inside the valence band on the p-side. Heavy doping on one side only would give an ordinary one-sided junction. The consequence is a depletion layer of about 10 nm — roughly a hundredth of that in a normal diode — thin enough for electrons to tunnel straight through the barrier rather than climb over it.
Statement (d) — the tunnel diode is indeed voltage controlled, so the statement is not itself objectionable. Its I–V curve is single-valued in V but multi-valued in I, which makes it an N-type (voltage-controlled) negative resistance, in contrast to the S-type curve of a device such as the UJT. But since (d) appears only in option 3, which also carries the false statement (c), it cannot rescue that option.
What the heavy doping produces. The forward characteristic rises to a peak current IP at about 50 mV, falls to a valley current IV, then rises again as ordinary injection takes over. Between peak and valley,
\(\dfrac{dI}{dV} \lt 0\)
and that negative differential resistance is what lets the device oscillate or amplify. Because tunnelling involves no minority-carrier storage or transit delay, it works into the millimetre-wave region.
Hence, the correct statements are (a) and (b).
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 :
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.
Which of the following statements are true for a zener diode ?
(a) The voltage across the zener resistance is zero.
(b) The diode is used as a constant voltage device.
(c) The diode is used as a varactor diode.
(d) The diode is formed of heavily doped p and n-type semiconductor.
Options :
Important Questions from Types of Diode
When we tune in any desired station in a radio receiver by rotating the tuning control we vary
Which of the following diode exhibits negative resistance in its I-V characteristics?
The peak point voltage and the valley point voltage are characteristics of a _________.
The following diodes are operated in reverse biased condition, EXCEPT ______.
A diode for which you can change the reverse bias and thus vary the capacitance is called
