Question

The primary characteristic of a tunnel diode is its _ _ _ _ .

• A. very high forward resistance
• B. negative resistance
• C. low breakdown resistance
• D. high capacitance

Hint:

The distinguishing feature of a tunnel diode is its negative resistance region, created by quantum mechanical tunneling across its extremely thin depletion layer.

Answer 1

The Correct Option is B

Understanding the Concept: A tunnel diode (also historically known as an Esaki diode) is a highly specialized semiconductor junction diode fabricated with exceptionally high doping concentrations (on the order of \(10^{19}\text{ cm}^{-3}\) or greater). Because of this heavy doping, the depletion region width becomes extremely thin (typically less than \(10\text{ nm}\)). This narrow barrier allows quantum mechanical tunneling to occur, enabling electrons to pass straight through the forbidden energy gap at small forward bias voltages. This produces a unique Current-Voltage (\(I-V\)) characteristic profile containing a distinct peak current point followed by a valley current point.

Step 1: Analyzing the negative differential resistance zone.
As the applied forward bias voltage is increased from zero, the tunneling current rises rapidly until it reaches its peak value (\(V_p, I_p\)). If the forward voltage is increased further beyond \(V_p\), the alignment of electron states in the conduction band with empty states in the valence band begins to decrease. Consequently, the quantum tunneling current drops continuously until it reaches its minimum at the valley point (\(V_v, I_v\)).

Step 2: Defining the characteristic behavior.
Within this specific operational interval between the peak voltage and the valley voltage, an increase in applied voltage causes a corresponding decrease in current. The slope of the \(I-V\) curve in this region is negative: \[ R_{\text{diff}} = \frac{\Delta V}{\Delta I} < 0 \] This unique property is called Negative Differential Resistance. This dynamic characteristic is highly valued because it allows tunnel diodes to be utilized in high-frequency relaxation oscillators, amplifiers, and switching circuits. This matches Option (B).