• drift current
The steady flow of charge carrier in one direction caused by the applied electric field constitutes electric current called drift current.
Jsc = q[ nun + pup ] E
=) Isc = q [ nun + pup ] E×A.
Where isc = drift current
And jsc = current density
Jsc = i/A
# Key points
• drift current is depend on its
(1) concentration of charge carrier
(2) electric field
(3) area
• Diffusion current
A second type of current is also exists in a semiconductor is called diffusion current.
Diffusion current is due to concentration gradient (charge carrier flows due to differences in concentration).
In n- type semiconductor
Concentration gradient = - dn/ dx
Jn = q Dn dn/dx
Where Dn = diffusion constant for free electrons
In p- type semiconductor
Concentration gradient = - dp/dx
Jp = - q Dp dp/dx
• Key points
Diffusion current is depend on
(a) Concentration gradient
(b) Thermal agitation ( change in temperature)
(c) Area
