Tunnel DiodeZulhilmi b Ab Rafit A124667

Introduction A Tunnel Diode is s pn junction that exhibits

negative resistance between two values of forward voltage

 voltage is increased the current through it decreases.

Introduction A pn junction with heavy doping of p type and n

type semiconductor materials results in large no of majority carriers Because this large no of carriers, most are not

used during initial recombination that produces depletion layer

Tunneling effect occurs

Theory p-n junction with highly doped regions creating

very thin barrier (depletion region)

Theory In such case, there is a probability that electrons

can tunnel from the conduction band of n-region to the valence band of p-region

Theory (a) the bottom of the n-side

conduction band overlaps the p-side valence band

(b) with a small forward bias electrons can directly tunnel across the small depletion region from the n-side conduction band into the p side valence band,

(c ) for increased forward voltage the tunnel current ceases as the two bands do not overlap anymore (regular pn junction)

Operation

Forward bias Also known as negative resistance As voltage begins to increase, electrons at first

tunnel pass through the very narrow p-n junction barrier

because filled electron states in the conduction band on the n-side become aligned with empty valence band hole states on the p-side of the pn junction.

As voltage increases further these states become more misaligned and the current drops

Forward Bias Zero bias, no current flow

Forward Bias Small forward bias, Potential barrier still very high Electron tunnel – tunnel current

Forward Bias Lager voltage Electron tunnel = Hole create Maximum tunneling current

Forward Bias Higher voltage #electron decrease at n-reagion start tunneling current decrease

Forward Bias Higher voltage Tunneling Current = 0 regular diode forward current due to electron –

hole injection increases due to lower potential barrier.

Forward Bias Higher voltage I-V characteristic similar to a regular p-n diode.

Reverse Bias electrons in the valence band of the p side tunnel

pass directly towards the empty states present in the conduction band of the n side

creating large tunneling current which increases with the application of reverse voltage.

Similar to zener diode