Understanding the Tunnel Diode's Distinctive I-V Characteristic
The question asks for the most unique characteristic of a tunnel diode's current-voltage ($I-V$) behavior. To answer this, we need to understand how a tunnel diode behaves electrically when voltage is applied across it, and compare this to other diodes.
Explaining the Tunnel Diode I-V Curve
A tunnel diode, also known as an Esaki diode, is engineered with very heavy doping levels on both its p-type and n-type sides. This heavy doping leads to a phenomenon called quantum mechanical tunneling, which significantly alters its standard diode $I-V$ characteristic. Typically, a diode's current increases monotonically with forward voltage. However, the tunnel diode has a unique region in its forward bias characteristic:
- At very low forward voltages, current starts flowing due to tunneling.
- As the forward voltage ($V$) increases, the current ($I$) initially increases up to a point called the peak current ($I_p$).
- Crucially, beyond this peak point, as the forward voltage ($V$) is increased further, the current ($I$) actually decreases. This occurs over a specific voltage range.
- This region, where current decreases as voltage increases, is known as the region of negative differential resistance (NDR). Mathematically, this means the slope of the $I-V$ curve, $\frac{dI}{dV}$, is negative in this range.
- After reaching a minimum point (valley current, $I_v$), the current starts increasing again, similar to a conventional diode.
Analysis of Provided Options
Let's evaluate each option based on the known $I-V$ characteristic of a tunnel diode:
| Option # | Description | Validity for Tunnel Diode |
| 1 | It has an extremely high reverse breakdown voltage. | Tunnel diodes do conduct in reverse bias, but they don't typically exhibit an *extremely high* reverse breakdown voltage as their primary or most distinctive feature. This is more characteristic of Zener diodes. |
| 2 | Its current is almost zero until a high forward voltage is applied. | This is incorrect. Due to the tunneling effect, tunnel diodes start conducting significantly even at very low forward voltages, not high ones. |
| 3 | It exhibits a region of negative differential resistance. | This is the most distinctive feature. The ability of the current to decrease as the voltage increases over a specific forward voltage range is unique and defines the operational capability of tunnel diodes in circuits like oscillators and high-frequency amplifiers. |
| 4 | It always maintains a constant current regardless of the applied voltage. | This is incorrect. The current in a tunnel diode varies significantly with applied voltage, especially around the peak and valley points. No semiconductor diode generally maintains a constant current over a wide voltage range. |
| 5 | (Empty) | Not applicable. |
| 6 | (Empty) | Not applicable. |
Identifying the Defining Feature
Comparing the options, the presence of a negative differential resistance (NDR) region in the forward bias characteristic is the most unique and defining property of a tunnel diode. While other diodes might have high reverse breakdown or low current at low voltages, the NDR region is exclusive to tunnel diodes (and a few other specific devices like Gunn diodes) and is what makes them valuable for specific electronic applications.
Important Questions from Diodes and Its Applications - Teaching
The electronic circuit that converts AC to DC where the DC output peak value can be greater than the AC input peak value is -
Which of the following statements are correct?
A. Schottky barriers are established by depositing a metal, such as Tungsten, on a p‐type channel.
B. The transfer characteristics of a depletion type MESFET are similar to those of a depletion type MOSFET.
C. Maximum operating conditions are determined by the product of drain‐to‐source voltage and drain current.
D. A complimentary MOSFET has negligibly small input impedance.
Choose the correct answer from the options given below:
Arrange the following in descending order of their switching times:
(A) Schottky diodes
(B) Power transistor (Darlington)
(C) IGBT
(D) Trine
Choose the correct answer from the options given below:
Arrange the following in decreasing order of the noise generated by them:
(A) Diode
(B) Transistor
(C) Avalanche photo diode
(D) FET
Choose the correct answer from the options given below:
The Schottky effect is the image force induced lowering of the potential energy for charge carrier emission when an electric field is applied. The attractive force called image force is:
