UNIT 1 – SPECIAL DIODES
,P-N Junction Diodes
• In semiconductor material, one half is doped by p-type impurity and other half is doped by N-type i
junction is formed.
• The plane dividing two hales or zones is called PN Junction.
• N-type – higher concentration of free electrons, P-type – High concentration of holes.
• Therefore, at the junction there is a tendency to diffuse over to the P-side from N-side, and from N-sid
called Diffusion.
• Free electrons move across the junction from N-type to P-type, the donor ions becomes +ve charged, th
is built on N-side of the junction.
• The free electrons uncover the negative acceptor ions by filling the holes. Therefore, a net –ve charge is e
the P-side of the junction.
, • On P-side, the net –ve charge prevents further diffusion of electrons into P-side. Similarly, the net +ve ch
side repels the hole crossing from P-side to N-side.
• Thus a barrier is set up, which is called as depletion layer, junction barrier or contact potential Vo.
• The magnitude of contact potential Vo varies with doping levels and temperature, 0.3 for germanium
silicon.
Forward Bias Condition
• When +ve terminal of battery is connected to P-type and -ve terminal to
N-type of PN junction diode, the bias is known as forward bias.
• The applied +ve potential repels the holes in P-type, and –ve potential
repels the electrons in the N-type.
• When applied potential is greater than barrier potential, the depletion
region and internal potential barrier disappear.
• When forward voltage (VF< Vo), then IF is almost Zero.
• For VF > Vo, then resulting in relatively large current flow in the circuit.
,P-N Junction Diodes
• In semiconductor material, one half is doped by p-type impurity and other half is doped by N-type i
junction is formed.
• The plane dividing two hales or zones is called PN Junction.
• N-type – higher concentration of free electrons, P-type – High concentration of holes.
• Therefore, at the junction there is a tendency to diffuse over to the P-side from N-side, and from N-sid
called Diffusion.
• Free electrons move across the junction from N-type to P-type, the donor ions becomes +ve charged, th
is built on N-side of the junction.
• The free electrons uncover the negative acceptor ions by filling the holes. Therefore, a net –ve charge is e
the P-side of the junction.
, • On P-side, the net –ve charge prevents further diffusion of electrons into P-side. Similarly, the net +ve ch
side repels the hole crossing from P-side to N-side.
• Thus a barrier is set up, which is called as depletion layer, junction barrier or contact potential Vo.
• The magnitude of contact potential Vo varies with doping levels and temperature, 0.3 for germanium
silicon.
Forward Bias Condition
• When +ve terminal of battery is connected to P-type and -ve terminal to
N-type of PN junction diode, the bias is known as forward bias.
• The applied +ve potential repels the holes in P-type, and –ve potential
repels the electrons in the N-type.
• When applied potential is greater than barrier potential, the depletion
region and internal potential barrier disappear.
• When forward voltage (VF< Vo), then IF is almost Zero.
• For VF > Vo, then resulting in relatively large current flow in the circuit.
