Question

Which of the following statements is not true?
A) The resistance of an intrinsic semiconductor decreases with temperature
B) Doping pure Si with trivalent impurities gives p-type semiconductor
C) The majority carriers in the n-type semiconductor are holes
D) A p-n junction can act as a semiconductor diode.

Answer 1

Hint: The p-type semiconductor has a trivalent impurity because in p-type semiconductor we have an excess number of holes. In a p-type semiconductor, the current will flow is due to the movement of holes inside the material.

Complete step by step solution:
Option A: The resistance of an intrinsic semiconductor decreases with temperature: at absolute zero temperature, all the electrons are there in the valence band. When the temperature is increased, then most of the electrons gain enthalpy (EGE) and then jump into the conduction band and so are responsible for the conductivity in the semiconductor. When we increase in temperature, the number of electrons increases in the valence band jumps into the conductance band which results in the increase in conductivity of the intrinsic semiconductor. As a result, with increase in the temperature, the conductivity of the intrinsic semiconductor increases.
$\text{conductivity}$ $\propto$ $\dfrac{1}{\text{Resistivity}}$
So, with an increase in temperature, resistivity can be decreased.

Option B: Doping pure Si with trivalent impurities gives p-type semiconductor: for a p-type semiconductor, p is known as positive, which means a semiconductor is rich in holes or a positively charged ions So when a semiconductor like Si is doped with a trivalent impurity, it will give us the p-type semiconductor.

Option C: The majority carriers in the n-type semiconductors are holes: In an N-type semiconductor, N stands for negative. An N-type semiconductor, the holes are the minority charge carriers and the electrons are the majority charge carriers. Hence the concentration of electrons is more than the concentration of the hole.

Option D: A p-n junction can act as a semiconductor diode: A p-n junction is a two-terminal or a two-electrode semiconductor device. It allows the electric current only in one direction while blocking the electric current in the opposite direction or a reverse direction. If the diode is forward biased, it will allow the electric current flow, and if the diode is reversed biased, it will block the electric current flow.

$\therefore$ The required answer: Option (B) is not true.

Note:
In a p-type semiconductor, the electrons and the holes are charge carriers but the number of holes is very large as compared to the number of electrons. The conductivity of the material can be defined as the extent to which the material can conduct electricity. For an intrinsic semiconductor, the number of electrons and the number of holes is equal.