1) The document discusses the theory of a PN junction diode, which is formed when a piece of semiconductor material is doped with a P-type impurity on one half and an N-type impurity on the other half. 2) At the junction, there is a tendency for free electrons to diffuse from the N-side to the P-side and holes to diffuse from the P-side to the N-side. This process is called diffusion. 3) A depletion region or width forms at the junction due to the space charge from donors on the N-side and acceptors on the P-side losing electrons and holes. An electric field is established across the junction, causing a potential

1. ANURAG COLLEGE OF ENGINEERING
(Approved by AICTE, New Delhi & Affiliated to JNTU-HYD)
Aushapur (V), Ghatkesar (M), Medchal(Dist.), Telangana-501 301.
ANALOG ELECTRONIC
TOPIC: PN-Junction DIODE
Presented By:
B. Raj Kumar
Assistant Professor
Department of ECE
Anurag College of Engineering

2. Theory of PN Junction Diode
In a piece of semiconductor material, if one half is doped
by P-type impurity and other half is doped by N-type
impurity, a PN junction. Is formed. The plane dividing the
two halves or zones is called PN-Junction Diode.

3. Density charge

4. • As shown in the above fig, the N-type material
has high concentration of free electrons.
• While P-type material has high concentration
of holes.
• Therefore, at the junction there is a tendency
for the free electrons to diffuse over P-side
and hoes to the N-side.
• This process is called DIFFUSION.

5. Calculation of Depletion Width or
Region
• Let us consider the width of depletion region in
the junction (fig 1.1). The region contains space
charge due to the fact that donors on N-side ND
and acceptors on P-side NA have lost their
accompanying electrons and holes.
• Hence an electric field is established which, in
turn, causes a difference in potential energy(qVo)
between the two parts of the specimen. Thus, a
potential is built up across the junction

6. • Fig 1.1e represents the variation in potential.
Here, the P-side of the Jn is at lower potential
than N-side which means that the electrons
on the P-side have greater potential energy.
• In this analysis, let us consider an Alloy Jn.
• In which there is an abrupt charge from
acceptor ions on P-side to Donor ions on N-
side .
• Assume that the conc. of e-’s & holes in the
depletion region is negligible and that all of
the donors and acceptors are ionized.

7. • Hence, the region of free space charge may be
described as
• From fig 1.1e, in such a way that V1 & X1 have
negative values. The potential in the space
charge region can be calculated by using
passions equation, which is given by,

8. • The relevant eqn for the required one
dimensional problem is
• Applying the eqn 3 to the P-side of the jn, we
get
• Integrating the above eqn twice, we get
• From fig1.1e, we have V=0 at X=0, and hence
D=0, when x<X1 on P-side, the potential is
constant, so that

9. If we apply the same procedure to N-side, we get

10. • Therefore, the total built-in potential or the
concept potential VO is given by
• We know that the +ve charge on N-side must
be equal in magnitude to the –ve charge on P-
side for neutral specimen. Hence
NAX1= NDX2
• By substuting this relationship in eqn 8 and
using the fact that X1 is –ve quantity, we get

11. • The total depletion width W=X2-X1 and hence
• By substuting for X2 andX1 , we get
• Hence in alloy jn, the depletion width W is
proportional to (Vo)
• In grown jn, the charge density varies
linearly with distance X (fig 1.1c).
• If a similar analysis is carried out for this jn, it
is found that W varies as

12. Reference
s
Integrated Electronics, Jacob
Miliman, McGraw-Hill
Education, 2010.
Electronic Devices and
Circuits- S. Salivahanan, N.
Suresh Kumar, McGraw-Hill
Education, 2018.
Electronic Devices and
Circuits theory– Robert L.
Boylestead, Louis Nashelsky,
11th Edition, 2009