Chapter 24.6, Problem 24.6.1SR

Interpretation Introduction

Interpretation: The group in the periodic table that contains elements which are semiconductors at room temperature should be determined.

Concept Introduction:

Semiconductors are substances that conduct electricity either by addition of an impurity or by the effects of temperature on it. Semiconductors have small energy gap between valence and conduction band hence its electrical conductivity lies between conductor and insulator.

Addition of impurity to a semiconductor is termed as doping. Doping alters the conductivity of a semiconductor. The addition of an element having either more or less number of valence electrons than the natural semiconductor decides the combination as the following two types of semiconductor.

• n- type semiconductor:  (conduction is due to movement of extra electrons)

The element added will have more valence electron than the natural semiconductor. Therefore, the extra electron from the added element resides in conduction band and increase the conductivity.

Example: Silicon (natural semiconductor) and Phosphorus

• p-type semiconductor: (conduction is due to movement of holes)

The element added will have less valence electron than the natural semiconductor. Here, instead of extra electron, there will be “holes” at the places, where a semiconductor is replaced by added element. A p-type semiconductor increases conductivity because the holes (effective positive charge; lies at valence band) move through the natural semiconductor rather than electrons.

Example: Silicon (natural semiconductor) and Gallium

Periodic Table: The available chemical elements are arranged considering their atomic number, the electronic configuration and their properties. The elements placed on the left of the table are metals and non-metals are placed on right side of the table and the elements that exhibits both metal and non-metals properties are placed in between metals and non-metals.

In periodic table the horizontal rows are called periods and the vertical column are called group.

There are seven periods and 18 groups present in the table and some of those groups are given special name as follows,

$\begin{array}{l}\text{Group-1}\to \text{Alkali metal}\\ \text{Group-2}\to \text{Alkaline metals}\\ \text{Group-16}\to \text{Chalcogens}\\ \text{Group-17}\to \text{Halogens}\\ \text{Group-18}\to \text{Noble gases}\end{array}$

Atomic Number: Atomic number of the element is equal to the number of protons present in the nucleus of the element which is denoted by symbol Z. The superscript presents on the left side of the symbol of the element.