To determination of the band-gap of the semiconductor using the four probe method.
In a crystalline solid as a result of interaction between tremendous numbers of atoms in the crystal the energy levels are split up and form bands of allowed energy which contains almost continuum of levels. The band which contains the valence electrons is called the valence band. The unoccupied energy levels also split up and form another band called conduction band. These energy bands are separated by a gap of forbidden energy termed as the band-gap.
The electrical conductivity in a semiconductor will be the sum of contribution of both electron and holes. In general it is given by the expression:
Distance between the probes(s) = 0.200cm
Thickness of the crystal (w) = 0.050 cm
Table for determination of determination of the resistivity of the semiconductor:
Current (I) = …..mA (constant).
K = 8.6 x 10-5 eV/deg & T is the temperature in Kelvin