•Diode current equation expresses the relationship between the current flowing through the diode as a function of the voltage applied across it.

•Mathematically it is given as,

Where, I is the current flowing through the diode

$\ I_0$ is the dark saturation current,

q is the charge on the electron,

V is the voltage applied across the diode,

η is the (exponential) ideality factor.

is the Boltzmann constant

T is the absolute temperature in Kelvin.

•In this equation, two parameters require to be discussed in quite detail. They are:

•Dark Saturation Current ($\ I_0$) : Dark saturation current indicates the leakage current density flowing through the diode in the absence of light (hence, ‘dark’). This parameter is the characteristic of the diode under consideration and indicates the amount of recombination which occurs within it. That is, I0 will be larger for a diode in which recombination rate is higher and vice versa. Further, its value is also seen to be directly proportional to the absolute temperature and inversely proportional to the material quality.

•(exponential) Ideality Factor (η ): Ideality factor indicates the nearness with which the considered diode behaves with respect to the ideal diode. That is, if the diode under consideration behaves exactly as that of an ideal diode, then η will be 1. Its value increases from 1 as the difference between the behaviors of the ideal diode and diode under consideration increases: greater is the deviation, greater is the value of η.