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Types of Solids

Based on various factors, solids have been categorized into conductors, insulators, and semiconductors, as given in Table.
 
Table Types of solid

Conductors
 
Properties
Conductors
Electrical conductivity
102 to 108/m
Resistivity
10–2 to 10–8 -m (negligible)
Band structure
107901.png
Energy gap (Eg)
Zero or very small
Current carriers
Free electrons
Condition of VB and CB at ordinary temperature
VB and CB are completely filled or CB is some what empty
Temperatureco-efficient of resistance
Positive
Effect of temperature on conductivity
Decreases
Effect of temperature on resistance
Increases
Examples
Cu, Ag, Au, Na, Pt, Hg, etc.
Electron density
1029/m3

Insulators
 
Properties
Insulators
Electrical conductivity
10–8 /m
Resistivity
108 -m
Band structure
107909.png
Energy gap (Eg)
Very large; for diamond, it is 6 eV
Current carriers
––
Condition of VB and CB at ordinary temperature
VB is completely filled.
CB is completely unfilled
Temperatureco-efficient of resistance
Zero
Effect of temperature on conductivity
Effect of temperature on resistance
Examples
Wood, plastic, mica, diamond, glass, etc.
Electron density

 

Semiconductors
 
Properties
Semiconductors
Electrical conductivity
10– 5 to 100/m
Resistivity
105 to 100 -m
Band structure
107915.png
Energy gap (Eg)
Ge  0.7 eV
Si  1.1 eV
GaAs 1.3 eV
GaF2  2.8 eV
Current carriers
Free electrons and holes
Condition of VB and CB at ordinary temperature
VB – somewhat empty
CB – somewhat filled
Temperatureco-efficient of resistance
Negative
Effect of temperature on conductivity
Increases
Effect of temperature on resistance
Decreases
Examples
Ge, Si, Ga, As, etc.
Electron density
Ge ~ 1019 /m3
Si ~ 1016 /m3




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