More Wave Equation Solutions Leading To Energy Bands 3 and 5 February 2014

Electron Effective Mass For electrons in semiconductor lattice, Analogy to free electron, and, Free electron mass For example, in Si in GaAs, The bottom part of conduction band can be approximated by the parabola. 13 13

Conduction Band and Valence Band For valence band holes Ec Ev For conduction band electrons Bandgap k E 15 15

Conduction band (empty) Band Structure of Insulators Eg Conduction band Valence band Eg Filled with few electrons Filled with few holes Conduction band (empty) Valence band (full) T > 0 K T = 0 K Few number of electrons and holes results in poor conductivity 19 19

Conduction band (empty) Band Structure of Semiconductors Conduction band (empty) Valence band T > 0 K Eg Filled with some electrons Filled with some holes Conduction band Eg Valence band (full) T = 0 K Significant number of electrons and holes results in higher conductivity than insulator 20 20

Band Structure of Metals Occupied band Empty band Band overlap T = 0 K It is easy for the electrons to jump into the empty levels, so metals have high conductivity. 21 21

Concept of Hole The movement of a valence electron into a empty state is equivalent to the movement of the positively charged empty state itself Movement of holes can also give rise to a current Each hole carries 1.6Х10-19 (C) of charge 22 22