Test: Properties Of Semiconductors - Mechanical Engineering MCQ

A semiconductor is a solid which has the energy band similar to that of the insulator. It acts as an insulator at absolute zero.

When the temperature is raised or when impurity is added, their conductivity increases. Conductivity is inversely proportional to temperature.

Semiconductors have negative temperature co-efficient. The reason for this is, when the temperature is increased, a large number of charge carriers are produced due to breaking of covalent bonds and hence these electrons move freely and gives rise to conductivity.

In conductors, electrons are charge carriers. But in semiconductors, both electrons and holes are charge carriers and will take part in conduction.

The elemental semiconductor is made up of single element from the fourth column elements such as Germanium. Here recombination takes place takes place via traps. It is called indirect bad gap semiconductors.

The compound semiconductors are made by combining the third and fifth column elements. Such as GaAs are made by combining third and fifth column elements.

In compound semiconductors, recombination takes place directly and its energy difference is emitted in the form of photons in the visible or infrared range. Hence the compound semiconductors are also knows as direct band gap semiconductors.

Impure semiconductors in which the charge carriers are produced due to impurity atoms are called extrinsic semiconductors. They are obtained by doping an intrinsic semiconductor with impurity atoms.

 N-type semiconductor is obtained by doping an intrinsic semiconductor with pentavalent impurity atoms.

 P-type semiconductor is obtained by doping an intrinsic semiconductor with trivalent impurity.

 When a conductor carrying current is placed in a transverse magnetic field, an electric field is produced inside the conductor in a direction normal to both the current and the magnetic field. This phenomenon is known as Hall Effect.

Conductivity of an intrinsic semiconductor = n_ie(μ_e+μ_h)
Conductivity = 2.32
Resistance = ρl/A = l/(conductivy ×A)
Resistance = 4310 ohm

Hall coefficient = (V_H b)/(I_H B)
Hall coefficient = 3.7×10^-6 m³/C

 Conductivity = n_ie(μ_e+μ_h)
Conductivity = 2.12352/ohm m
Resistivity = 1/Conductivity
Resistivity = 0.4709ohm m

V_H = (R_H I_H B)/t
V_H = 1.83×10^-3 Volts