Chapter 24, Problem 24.29QP

Interpretation Introduction

Interpretation: The only elemental semiconductors ( $\text{Si}$, $\text{Ge}$, and graphite) are members of Group 4A.  $\text{Sn}$ and $\text{Pb}$ are also in Group 4A, but are not classified as semiconductors has to be explained.

Concept Introduction:

Band theory helps to study about conductors, semiconductors and insulators. The electrons of an atom will be in permitted energy levels.  These energy levels form bands. Three types of bands are available namely,

• Filled band- (found near nucleus, bears no free electrons)
• Valence band- (last band bearing valence electrons, these are free electrons)
• Conduction band – (accepts free electrons escaping from valence band)

These bands help to explain conductivity of elements.  All the bands will lie in different energy levels.  When a free electron from valence band escapes into conduction band, conductivity takes place.  The energy gap between valence band and conduction band decides the conductivity of an element.

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