What is a tunnel diode and how does it exhibit negative resistance?
1 Answer
A tunnel diode, also known as an Esaki diode, is a special type of semiconductor diode that exhibits a phenomenon called "negative resistance." It was first discovered by Japanese physicist Leo Esaki in 1958, and it plays a crucial role in certain electronic applications, particularly in high-frequency oscillators and microwave devices.
A regular diode allows current to flow in one direction, from the anode (positive side) to the cathode (negative side), while offering a high resistance in the opposite direction. In contrast, a tunnel diode demonstrates negative resistance in a specific voltage range.
Here's how a tunnel diode works and how it exhibits negative resistance:
Quantum tunneling: The unique property of a tunnel diode arises from a quantum mechanical phenomenon called "quantum tunneling." Under normal circumstances, electrons require sufficient energy to overcome the energy barrier between the semiconductor materials of the diode. However, in a tunnel diode, due to its specific construction and materials, some electrons are able to tunnel directly through the energy barrier without needing as much energy.
Energy band diagram: A regular diode has a single energy barrier that electrons must overcome to move from one side to the other. In a tunnel diode, there are two closely spaced energy barriers within the semiconductor material. This leads to an overlap in the conduction bands of the two regions.
Negative resistance region: When a small forward voltage is applied across the tunnel diode, electrons with sufficient energy can quantum tunnel through the thin energy barrier. As the voltage is increased further, the current decreases slightly due to the depletion region forming around the diode. However, as the voltage is further increased to a specific voltage range (called the "negative resistance region"), the quantum tunneling effect dominates, leading to a sudden increase in current instead of the expected decrease. This behavior is the opposite of what is observed in conventional diodes, hence the term "negative resistance."
Oscillations: The negative resistance region allows the tunnel diode to be used as a high-frequency oscillator. When connected to a resonant circuit, the tunnel diode's negative resistance causes the circuit to generate and sustain high-frequency oscillations.
Limited voltage range: It's essential to note that the negative resistance region is limited to a specific voltage range, and outside this range, the tunnel diode behaves like a regular diode.
Tunnel diodes are less commonly used in modern electronic devices due to the advancement of other semiconductor technologies. However, their unique characteristics and ability to operate at high frequencies still find applications in certain niche areas where high-frequency oscillation and negative resistance are required.
A regular diode allows current to flow in one direction, from the anode (positive side) to the cathode (negative side), while offering a high resistance in the opposite direction. In contrast, a tunnel diode demonstrates negative resistance in a specific voltage range.
Here's how a tunnel diode works and how it exhibits negative resistance:
Quantum tunneling: The unique property of a tunnel diode arises from a quantum mechanical phenomenon called "quantum tunneling." Under normal circumstances, electrons require sufficient energy to overcome the energy barrier between the semiconductor materials of the diode. However, in a tunnel diode, due to its specific construction and materials, some electrons are able to tunnel directly through the energy barrier without needing as much energy.
Energy band diagram: A regular diode has a single energy barrier that electrons must overcome to move from one side to the other. In a tunnel diode, there are two closely spaced energy barriers within the semiconductor material. This leads to an overlap in the conduction bands of the two regions.
Negative resistance region: When a small forward voltage is applied across the tunnel diode, electrons with sufficient energy can quantum tunnel through the thin energy barrier. As the voltage is increased further, the current decreases slightly due to the depletion region forming around the diode. However, as the voltage is further increased to a specific voltage range (called the "negative resistance region"), the quantum tunneling effect dominates, leading to a sudden increase in current instead of the expected decrease. This behavior is the opposite of what is observed in conventional diodes, hence the term "negative resistance."
Oscillations: The negative resistance region allows the tunnel diode to be used as a high-frequency oscillator. When connected to a resonant circuit, the tunnel diode's negative resistance causes the circuit to generate and sustain high-frequency oscillations.
Limited voltage range: It's essential to note that the negative resistance region is limited to a specific voltage range, and outside this range, the tunnel diode behaves like a regular diode.
Tunnel diodes are less commonly used in modern electronic devices due to the advancement of other semiconductor technologies. However, their unique characteristics and ability to operate at high frequencies still find applications in certain niche areas where high-frequency oscillation and negative resistance are required.