1. Other diodes Electronic device and circuit Active learning assignments
(Tunnel diodes, Step recovery diodes , Back diodes, PIN diodes)
Guided By:
JANKI N. CHOTAI
SVIT,VASAD
Made By:
Dhaval patel ( )
Marvik patel( )

2. Tunnel DIodes
The tunnel diode has negative resistance. It will actually conduct well with low forward bias. With further increases in bias it reaches the negative resistance range where current will actually go down. This is achieved by heavily-doped p and n materials that creates a very thin depletion region.
The semiconductor material used for constructing tunnel diode are Germanium or gallium arsenide.
Tunnel diode is used as high speed switch, in digital network, as a high frequency oscillator.
Most important application of a tunnel diode is in high speed computers where the switching time is in nanosecond.

3. Tunnel Diodes Reverse characteristics: Forward characteristics:
When the Tunnel diode is reverse biased, heavy doping of p and n sides, the depletion region is extremely narrow.
Therefore the reverse blocking of the junction is lost and reverse current will start flowing as soon as small reverse voltage is applied.
Thus the tunnel diode allows the conduction to take place for all the reverse voltages. There is no breakdown effect as observed in the conventional rectifier diode.
Therefore we can not use the tunnel diode as a rectifier
Forward characteristics:
It can be divided into three region namely X to Y, Y to Z, and z onwards.
Region X to Y: In this region the forward voltage Vf is extremely small. But heavy conduction will take place in this region. Because electron “tunnel ” through the p-n junction.
Region Y to Z: in this region, at point Y the forward voltage begins to develop a barrier and the forward current starts decreasing inspite of continued increase in Vf. This region is called as the negative resistance region.
Region Z: At point Z.the current starts increasing with increase in voltage.so this is a positive resistance region and the tunnel diode acts as the conventional diode.

4. step-recovery diodes
The doping of step-recovery diode is slightly unusual, the density of charge carriers (electron and holes) decrease near the junction.
The step-recovery diode is also known as Snap diode.
The operation of step-recovery diode during the positive half cycle is same as that of a silicon diode. But during negative half cycle reverse current flows for sometime due to the storage charge then suddenly reduce to zero.
The step-recovery diode is used for fast switching applications. This is achieved by reduced doping at the junction.
The step-recovery diode is used in the frequency multiplier circuits.

5. Pin diodes

6. Pin diodes
When a PIN diode is reverse biased, the electrons and holes move in opposite directions to “sweep free” the intrinsic material off electrons and holes.
It is important to note that the length of the length “L” of the depletion region in PIN diodes is approximately same as that of the intrinsic i-region.
When a PIN diode is forward biased, holes from the p layer will diffuse into the I-layer. They will attract equal number of holes from the n side.
This double injection of charged particles will reduce the resistivity of the i-region. In other conductivity increases.
Depending on the forward voltage, the conductivity of the i-layer will keep changing. This is known as the “ conductivity modulation ”of PIN diode.

7. Back diodes
The reverse breakdown voltage of a zener diode is <2V. By increasing the doping levels it is possible for us to get the breakdown at very low reverse voltage(typically ~0.1v). This diode is known as a BACK DIODE.
Back diode conducts better when it connected in reverse bias than forward bias.
Back diode shares same symbolic representation as that of a zener diode .
Back diode are used for rectifying weak signals having amplitudes between 0.1 and 0.7 volts.