B.2
Equation (B.2) is known as the Shockley equation that describes the current-voltage
behaviour of an ideal p-n diode. It is a fundamental equation for microelectronics device
physics.
J-V characteristic under illumination
When a p-n junction is illuminated the additional electron-hole pairs are generated through
the junction. In the case of moderate illumination the concentration of majority carriers
does not change significantly while the concentration of minority carriers (electrons in the
p-type region and holes in the n-type region) will strongly increase. In the following
section it is assumed that the photo generation rate, G, is uniform throughout the p-n
junction, this is called the uniform generation-rate approximation. This assumption
reflects the situation where the device is illuminated with a long wavelength light, which
is weakly absorbed by the semiconductor. The concentration of charge carriers in a p-n
junction with uniform photo generation rate is schematically presented in Figure B.2.
Figure B.2: Concentration profiles of mobile charge carriers in an illuminated p-n junction with uniform generation rate
G (red line). Concentration profiles of charge carriers under equilibrium conditions are shown for comparison (black
line).
Eqs. (B.6a) described the steady-state situation for minority carriers. In Section B.1
we then proceeded with assuming that the generation rate is zero. Now we analyse the
case where the junction is illuminated, i.e. the generation rate is not zero. The equations
thus can be rewritten:
Under the assumption that G/D N and G/D P are constant, the general solution to Eq. (B.14)
Equation (B.2) is known as the Shockley equation that describes the current-voltage
behaviour of an ideal p-n diode. It is a fundamental equation for microelectronics device
physics.
J-V characteristic under illumination
When a p-n junction is illuminated the additional electron-hole pairs are generated through
the junction. In the case of moderate illumination the concentration of majority carriers
does not change significantly while the concentration of minority carriers (electrons in the
p-type region and holes in the n-type region) will strongly increase. In the following
section it is assumed that the photo generation rate, G, is uniform throughout the p-n
junction, this is called the uniform generation-rate approximation. This assumption
reflects the situation where the device is illuminated with a long wavelength light, which
is weakly absorbed by the semiconductor. The concentration of charge carriers in a p-n
junction with uniform photo generation rate is schematically presented in Figure B.2.
Figure B.2: Concentration profiles of mobile charge carriers in an illuminated p-n junction with uniform generation rate
G (red line). Concentration profiles of charge carriers under equilibrium conditions are shown for comparison (black
line).
Eqs. (B.6a) described the steady-state situation for minority carriers. In Section B.1
we then proceeded with assuming that the generation rate is zero. Now we analyse the
case where the junction is illuminated, i.e. the generation rate is not zero. The equations
thus can be rewritten:
Under the assumption that G/D N and G/D P are constant, the general solution to Eq. (B.14)