defination of tunnel diode , working, application
- 1. TUNNEL DIODE (Esaki Diode) • It was introduced by Leo Esaki in 1958. • Heavily-doped p-n junction – Impurity concentration is 1 part in 10^3 as compared to 1 part in 10^8 in p-n junction diode • Width of the depletion layer is very small (about 100 A). • It is generally made up of Ge and GaAs. • It shows tunneling phenomenon. • Circuit symbol of tunnel diode is : EV
- 2. WHAT IS TUNNELING • Classically, carrier must have energy at least equal to potential-barrier height to cross the junction . • But according to Quantum mechanics there is finite probability that it can penetrate through the barrier for a thin width. • This phenomenon is called tunneling and hence the Esaki Diode is know as Tunnel Diode.
- 3. - Ve Resistance Region Vf Vp Ip Vv Forward Voltage Reverse voltage Iv Reverse Current Forward Current Ip:- Peak Current Iv :- Valley Current Vp:- Peak Voltage Vv:- Valley Voltage Vf:- Peak Forward Voltage CHARACTERISTIC OF TUNNEL DIODE
- 4. ENERGY BAND DIAGRAM Energy-band diagram of pn junction in thermal equilibrium in which both the n and p region are degenerately doped.
- 5. -Zero current on the I-V diagram; -All energy states are filled below EF on both sides of the junction; AT ZERO BIAS Simplified energy-band diagram and I-V characteristics of the tunnel diode at zero bias.
- 6. -Electrons in the conduction band of the n region are directly opposite to the empty states in the valence band of the p region. -So a finite probability that some electrons tunnel directly into the empty states resulting in forward-bias tunneling current. AT SMALL FORWARD VOLTAGE Simplified energy-band diagram and I-V characteristics of the tunnel diode at a slight forward bias.
- 7. -The maximum number of electrons in the n region are opposite to the maximum number of empty states in the p region. - Hence tunneling current is maximum. AT MAXIMUM TUNNELING CURENT Simplified energy-band diagraam and I-V characteristics of the tunnel diode at a forward bias producing maximum tunneling current.
- 8. -The forward-bias voltage increases so the number of electrons on the n side, directly opposite empty states on the p side decreases. - Hence the tunneling current decreases. AT DECREASING CURRENT REGION Simplified energy-band diagram and I-V characteristics of the tunnel diode at a higher forward bias producing less tunneling current.
- 9. -No electrons on the n side are directly opposite to the empty states on the p side. - The tunneling current is zero. -The normal ideal diffusion current exists in the device. AT HIGHER FORWARD VOLTAGE Simplified energy-band diagram and I-V characteristics of the tunnel diode at a forward bias for which the diffusion current dominates.
- 10. - Electrons in the valence band on the p side are directly opposite to empty states in the conduction band on the n side. -Electrons tunnel directly from the p region into the n region. - The reverse-bias current increases monotonically and rapidly with reverse-bias voltage. AT REVERSE BIAS VOLTAGE
- 11. Cj -R rs Ls TUNNEL DIODE EQUIVALENT CIRCUIT •This is the equivalent circuit of tunnel diode when biased in negative resistance region. •At higher frequencies the series R and L can be ignored. •Hence equivalent circuit can be reduced to parallel combination of junction capacitance and negative resistance.