Ideal Diodes

The diode equation gives an expression for the current through a diode as a function of voltage. The Ideal Diode Law, expressed as:

where:
I = the net current flowing through the diode;
I₀ = "dark saturation current", the diode leakage current density in the absence of light;
V = applied voltage across the terminals of the diode;
q = absolute value of electron charge;
k = Boltzmann's constant; and
T = absolute temperature (K).

The "dark saturation current" (I₀) is an extremely important parameter which differentiates one diode from another. I₀ is a measure of the recombination in a device. A diode with a larger recombination will have a larger I₀.

Note that:

• I₀ increases as T increases; and
• I₀ decreases as material quality increases.

At 300K, kT/q = 25.85 mV, the "thermal voltage".

Non-Ideal Diodes

For actual diodes, the expression becomes:

where:
n = ideality factor, a number between 1 and 2 which typically increases as the current decreases.

The diode law is illustrated for silicon.

The diode law for silicon - current changes with voltage and temperature. For a given current, the curve shifts by approximately 2 mV/°C.