In this lecture, we are going to learn about the Hall effect, the principle of the Hall effect, the theory & derivation of the Hall effect, the derivation of the Hall coefficient, and the application of the Hall effect in a very detailed manner. So let’s start with the knowledge of the principle of the Hall effect.
Principle of Hall Effect
If a specimen ( metal or semiconductor) carrying a current I is placed in a transverse magnetic field B, an electric field E is induced in the direction of perpendicular to both I and B. This phenomenon is known as Hall Effect and the generated voltage is called Hall voltage.
Theory & Derivation of Hall effect
 Consider a rectangular slab of an ntype semiconductor material that carries a current I along the positive Xdirection, as shown in the figure below.
 In an ntype semiconductor, electrons are the majority carriers.
 Let a magnetic field B be applied along the positive Zdirection. Under the influence of this magnetic field, the electron experience a force called Lorentz force given by,
F_L=Bev_d ……(1)
Where e is the magnitude of the charge of the electrons and V_{d} is the drift velocity.
 This Lorentz force is exerted on the electrons in the negative Ydirection. The direction of this force is given by Fleming’s lefthand rule. Thus, the electrons are, therefore, deflected downwards and collect at the bottom surface of the specimen.
 On the other hand, the top edge of the specimen becomes positively charged due to the loss of electrons. Hence, a potential called the Hall voltage V_{H} is developed between the upper and lower surfaces of the specimen, which establishes an electric field E called the Hallfield across the specimen in the negative Ydirection.
 This electric field exerts an upward force on the electron and is given by,
F_E=eE_H ……(2)
 At equilibrium, the Lorentz force and electric force get balanced. Hence,
F_E=F_L
 Therefore, from equations (1) and (2)
eE_H=Bev_d
or E_H=Bv_d ……(3)
 If b is the width (i.e., the distance between the top and bottom surface) of the specimen, then
E_H=\frac{V_H}{b} ……(4)
or V_H=E_Hb …….(5)
and V_H=Bv_db ……(6)
 Let t be the thickness of the specimen along the Zdirection. Therefore, its area of crosssection normal to the direction of current is bt.
 If J is the current density then,
J=\frac{I}{bt} ……(7)
 But J can also be expressed as
J=n_eev_d ……(8)
where n_{e} is the density of electrons.
\therefore \; v_d=\frac{J}{n_ee} ……(9)
 Hence, substituting equation (9) in (6),
V_H= Bb\; \frac{J}{n_ee} ……(10)
 But V_{H} is also equal to E_{H}b
\therefore \; E_Hb= Bb\;\frac{J}{n_ee}
or E_H = \frac{BJ}{n_ee} ……(11)
Hall Coefficient formula
 The Hall Effect is described by means of Hall Coefficient R_{H}. It is given by,
R_H=\frac{1}{ne}
where n is, in general, the carrier concentration.
R_{H} for ntype and ptype material
 A negative sign is used while denoting the Hall coefficient for an ntype material, i.e., it is given by
R_H=\frac{1}{ne} ……(12)
where n_{e} is the density of electrons.
 But for ptype material, a positive sign is used to denote the Hall coefficient, i.e., it is given by
R_H=\frac{1}{ne} ……(13)
where n_{h} is the density of holes.
 Therefore, equation (11) can be written as
E_H=BJR_H
\therefore \; R_H=\frac{E_H}{JB} ……(14)
 But we Know E_H=\frac{V_H}{b} \;and \; J = \frac{I}{bt}. Hence equation (14) becomes,
R_H=\frac{V_Hbt}{IBb}
\therefore \; R_H=\frac{V_Ht}{IB} ……(15)
 Since the quantities V_{H}, t, I and B are measurable, the Hall coefficient R_{H} can be determined.
Mobility Determination from Hall Effect
 For ntype material the conductivity is given by,
\sigma_e=n_ee\mu_e
where \mu_e is the mobility of electrons.
\therefore \; \mu_e=\frac{\sigma_e}{n_ee} ……(16)
or \therefore \; \mu_e=\sigma_e R_H ……(17)
 Similarly, for ptype material, the conductivity is given by,
\sigma_h=n_he\mu_h
where \mu_h is the mobility of holes.
\therefore \; \mu_h=\frac{\sigma_h}{n_he} ……(18)
or \therefore \; \mu_h=\sigma_h R_H ……(19)
 In the above discussion, it is assumed that all the charge carriers travel with average velocity. But actually, the charge carriers have a random thermal distribution in velocity.
 With this distribution taken into consideration, R_{H} is defined in general as,
R_H = \frac{3\pi}{8ne}\;=\frac{1.18}{ne} ……(20)
Therefore, equations (16) and (18) can be written as,
\mu_e \;= \frac{\sigma_eR_H}{1.18} ……(21)
\mu_h \;= \frac{\sigma_hR_H}{1.18} ……(22)
Application of Hall Effect
The Hall effect can be used for:
 Determining whether a semiconductor is ntype and ptype.
 Determining the carrier concentration and mobility.
 Determining the magnetic field B in terms of Hall voltage V_{H}.
 Designing the gauss meter and electronics meters based on Hall voltage.
Frequently Asked Question on Hall Effect

Name one practical use of Hall effect.
Hall effect is used to determine if a substance is a semiconductor or an insulator. The nature of the charge carriers can be measured.

How is Hall potential developed?
When a currentcarrying conductor in the presence of a transverse magnetic field, the magnetic field exerts a deflecting force in the direction perpendicular to both magnetic field and drift velocity. This causes charges to shift from one surface to another thus creating a potential difference.

What is a Hall effect sensor?
A Hall effect sensor is a device that is used to measure the magnitude of a magnetic field.

In the Hall effect, the direction of the magnetic field and electric field are parallel to each other. True or False?
False. The magnetic field and electric field are perpendicular to each other.
Also Read:
[…] Ans: When a semiconductor is placed under influence of the magnetic field, and a current is passed, an electric field is induced in a direction perpendicular to both I(current) and B(Magnetic field). The direction of filed induced remains the same irrespective of charge carriers. This force is Lorentz force and it results in the accumulation of negative & positive charges on top and bottom surfaces. This results in the induction of a field called as Hall Effect. […]
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