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

13. 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

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

19. 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

20. 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

21. 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

22. 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