Semiconductors 2

P-N
Junction
Diode
Jayant Nagda
JEE Coach & Motivational Speaker

B.Tech, IIT Bombay

IIT-JEE AIR - 161
12+ Years of Teaching Experience
Trained Million+ students
Best Content Award
livedaily.me/jee
Telegram Channel
 Unacademy
Subscription

LIVE Class Environment Performance Analysis

LIVE Polls & Leaderboard Weekly Test Series
LIVE Doubt Solving DPPs & Quizzes
LIVE Interaction
 Top Results

Bratin Mondal Amaiya Singhal

100 %ile 100 %ile

 India’s BEST Educators Unacademy Subscription

If you want to be the BEST

“Learn” from the BEST
Types of Semiconductors
1. Intrinsic semiconductor
A Pure Semiconductor is called intrinsic semiconductor.
It has thermally generated current carriers.

1. They have four electrons in the outermost orbit of

atom and atoms are held together by covalent bond
2. Free electrons and holes both are charge carriers and
ne(in C.B.) = nh(in V.B.)
Types of Semiconductors
1. Intrinsic semiconductor

3. In pure semiconductor, impurity must be less than 1 in 108 parts.

4. Because of less number of charge carriers at room temperature,

intrinsic semiconductors have low conductivity so they have no practical use.

5. For them fermi energy level lies

at the centre of the C.B. and V.B.
Extrinsic Semiconductor

1. It is also called impure semiconductor.

2. The process of adding impurity is called Doping.
Extrinsic Semiconductor

Pentavalent Impurity

The elements whose atom has five valence

electrons are called Pentavalent impurities

e.g. As, P, Sb etc.

These are also called donor impurities.

They donates extra free electron.

Also called N-type Semiconductors

Extrinsic Semiconductor

Trivalent Impurity

The elements whose each atom has

three valence electrons are called
trivalent impurities

e.g. In, Ga, Al, B, etc.

These impurities are also called

acceptor impurities as they accept
electron.

Also called P-type Semiconductors

A small impurity is added to germanium to get a
p-type semiconductor. This impurity is a -

A. trivalent substance
B. pentavalent substance
C. bivalent substance
D. monovalent substance
 N-type Semiconductors P-type Semiconductors

Majority charge carriers – electrons Majority charge carriers – holes

Minority charge carriers – Minority charge carriers –

holes electrons

ne >> nh ; ie >> ih nh >> ne ; ih >> ie

Conductivity σ ≈ neμee Conductivity σ ≈ nhμhe

A semiconductor is known to have an
electron concentration of 8 × 1013 per cm3 and
hole concentration of 5 × 1012 per cm3.
The semiconductor is -

A. n-type B. p-type

C. intrinsic D. none of these

Net Current and Conductivity

In intrinsic semiconductor, ne = nh
and in extrinsic semiconductors;

n-type, ne >> nh
and p-type, ne << nh

If ni is the charge density of either type of

charge carrier (in intrinsic semiconductor),
then
The number density of electrons and holes in pure silicon at
27oC are equal and its value is 2.0 x 1016 m-3. On doping with
indium the hole density increases to 4.5 x 1022 m-3, the
electron density in doped silicon is -

A. 10 x 109 m-3 B. 8.89 x 109 m-3

C. 11 x 109 m-3 D. 16.78 x 109 m-3
Net Current and Conductivity
When some potential difference is applied across a
piece of intrinsic semiconductor current flows in it
due to both electron and holes

where ve = drift velocity of electron,

vh = drift velocity of holes,

Hence conductivity of semiconductor

If the ratio of the concentration of electrons to that of holes
in a semiconductor is 7/5 and the ratio of currents is 7/4,
then what is the ratio of their drift velocities?
[AIEEE 2006]

A. 5/8 B. 4/5

C. 5/4 D. 4/7
Holes 1. Holes acts as virtual positive charge,
although there is no physical charge on it.
2. Effective mass of hole is more than electron.
3. Mobility of hole is less than electron.
4. holes are usually slower because they stay in
the valence energy band while electrons can be
in the conduction bands.
5. The drift velocity of
electrons (ve) is
greater than that
of holes (vh)
 N-type Semiconductors P-type Semiconductors

N-type semiconductor is electrically P-type semiconductor is also

neutral (not negatively charged) electrically neutral (not positively
charged)
An n-type semiconductor is -
A. negatively charged
B. positively charged
C. neutral
D. negatively or positively charged
depending upon the amount of impurity
If n-type semiconductor is heated then -

A. the number of electrons increases and the

number of holes decrease.
B. the number of holes increases and the number
of electrons decreases.
C. the number of electrons and holes both remain
Equal.
D. the number of both electrons and holes increases
 N-type Semiconductors P-type Semiconductors

Impurity is called Donor impurity because

one impurity atom generate one e– Impurity is called Acceptor impurity.

Donor energy level lies just below the Acceptor energy level lies just above
conduction band. the valence band.
Which of the following energy band diagram shows the N-
type semiconductor

A. B.

C. D.
The electrical conductivity of a semiconductor increases
when electromagnetic radiation of wavelength shorter
than 2480 nm is incident on it. The band gap in (eV) for
the semiconductor is
[AIEEE 2005]

A. 2.5 eV B. 1.1 eV

C. 0.7 eV D. 0.5 eV
P-N junction Diode

P–type N–type
semiconductor crystal semiconductor crystal
having acceptor impurities having donor impurities

When a P-type semiconductor is suitably joined

to an N-type semiconductor, then resulting arrangement
is called P-N junction or P-N junction diode
P-N junction Diode

Circuit Symbol for p-n Junction Diode:

The arrow-head represents the p-region and

the bar represents the n-region of the diode.

The direction of the arrow is from p to n and

indicates the direction of conventional current
flow under forward bias.

The p -side is called 'anode' and

the n -side is called 'cathode’.
P-N junction Diode

Due to difference in the concentration of charge carriers

in the two sections Electrons from N-region diffuse through
the junction into P-region and the hole from P region diffuse
into N-region
Depletion Region

p-type n-type
Semiconductor Semiconductor
Depletion Region

p-type n-type
Semiconductor Semiconductor

Holes in the
P-region are
occupied with
electrons and
N-region is left
with deficiency of
electrons i.e. with
positive ions
The region on either of the junction which becomes
depleted (free) of the mobile charge-carriers is called
the 'depletion region'.
Depletion layer in the p-n junction consists of -

A. Electrons

B. Holes
C. Positive and negative ions fixed in their position

D. Both electrons and holes

In p-n junction what is the direction
of internal electric field -

A. From p to n

B. From n to p

C. Perpendicular to the p-n junction

D. There is no electric field

Potential Barrier

The potential difference created across the P-N junction due to

the diffusion of electron and holes is called potential barrier.

for Ge VB = 0.3 V and

for Silicon VB= 0.7 V

On the average the potential barrier in P-N junction

is ~ 0.5 V and the width of depletion region ~ 10–6 m.

So the Barrier Electric Field,

The depletion layer in silicon diode is 1 μm wide and
the knee potential is 0.7 V, then the electric field in
the depletion layer will be -

A. Zero B. 0.7 Vm-1

C. 7 x 104 Vm-1 D. 7 x 105 Vm-1

Important Graphs
Important Graphs
Important Graphs

Charge Density Electric field Potential

P N N P N
P
+ve
-ve

Distance Distance Distance

 In a P-N junction diode which is not connected to
any circuit-
[IIT JEE 1998]
A. Potential is the same everywhere
B. The P-type side is at a higher potential than the N-
type side
C. There is an electric field at the junction directed from
the N-type side to the P-type side
D. There is an electric field at the junction directed from
the P-type side to the N-type side

Ans: C
 If ne and nh are the number of electrons and holes in a
semiconductor heavily doped with phosphorus, then -

A. ne >> nh B. ne ≤ nh
C. ne << nh D. none

Ans: A
 In a p–type semiconductor the acceptor level is situated
57 meV above the valence band. The maximum wavelength
of light required to produce a hole will be –

A. 57 Å B. 57 × 10–3 Å
217100 Å
C. D. 11.61 × 10–33 m

Ans: C
Depletion Region

1. The thickness of depletion layer is 1 micron = 10–6 m.

1. Width of depletion layer

1. Depletion is directly proportional to temperature.

2. The P-N junction diode is equivalent to capacitor in
which the depletion layer acts as a dielectric.
 Which graph shows correct variation of electric field
across depletion layer of p-n junction -

A. B.

C. D.

Ans: C
 A potential barrier of 0.50 V exists across a P-N junction. If
the depletion region is 5.0 × 10–7 m wide, the intensity of the
electric field in this region is
A. 1.0 × 106 V/m

B. 1.0 × 105 V/m

C. 2.0 × 105 V/m

D. 2.0 × 106 V/m

Ans: A
 Potential barrier developed in a junction diode opposes-

A. Minority carriers in both regions only

B. Majority carriers

C. Electrons in N-region

D. Holes in P-region

Ans: B
A potential barrier of 0.50 V exists across a p-n junction.
(a) If the depletion region is 5.0 × 10–7 m wide, what is the
intensity of the electric field in this region ?
(b) An electron with speed 5.0 × 105 m/s approaches the p-n
junction from the n-side. With what speed will it enter the
p-side ?
 In p-type semiconductor the majority charge carriers are -

A. electrons

B. neutrons

C. holes

D. protons

Ans: C
 In N-type semiconductors, the concentration of
minority charge carriers mainly depends upon -

A. the doping technique

B. the doping ratio
C. the temperature of the material
D. None

Ans: C
Pure Si at 300K has equal electron (ne) and hole (nh)
concentrations of 1.5 × 1016 m–3. Doping by indium increases
nh to 3 × 1022 m–3. Calculate ne in the doped Si.

Ans:
7.5 × 109 m–3
 #JEELiveDaily Schedule

11th

Namo Sir | Physics Ashwani Sir | Chemistry Sameer Sir | Maths

6:00 - 7:30 PM 7:30 - 9:00 PM 9:00 - 10:30 PM

12th

Jayant Sir | Physics Anupam Sir | Chemistry Purnima Ma’am | Maths

1:30 - 3:00 PM 3:00 - 4:30 PM 4:30 - 6:00 PM
Telegram Channel
 Unacademy
Subscription

LIVE Class Environment Performance Analysis

LIVE Polls & Leaderboard Weekly Test Series
LIVE Doubt Solving DPPs & Quizzes
LIVE Interaction
 Top Results

Bratin Mondal Amaiya Singhal

100 %ile 100 %ile

 India’s BEST Educators Unacademy Subscription

If you want to be the BEST

“Learn” from the BEST
Plus ICONIC

11th / 9, 10
11th / 9, 10

12th / Drop
12th / Drop

JAYANTLIVE JAYANTLIVE
JAYANTLIVE
JAYANTLIVE
JAYANTLIVE
JAYANTLIV
E
JAYANTLIVE
हज़ारो सुकून छोड़ने
पड़ते हैं एक जुनून के
लिए !