TEMPERATURE EFFECTS
All photodiode characteristics are affected by changes in temperature. They include shunt resistance, dark current, breakdown voltage, responsivity and to a lesser extent other parameters such as junction capacitance.
Shunt Resistance and Dark Current:
There are two major currents in a photodiode dark current and shunt resistance. Diffusion current is the dominating factor in a photovoltaic (unbiased) mode of operation, which determines the shunt resistance. It varies as the square of the temperature. In photoconductive mode (reverse biased), however, the drift current becomes the dominant current (dark current) and varies directly with temperature. Thus, change in temperature affects the photodetector more in photovoltaic mode than in photoconductive mode of operation.
In photoconductive mode the dark current may approximately double for every 10 ºC increase change in temperature. And in photovoltaic mode, shunt resistance may approximately double for every 6 ºC decrease in temperature. The exact change is dependent on additional parameters such as the applied reverse bias, resistivity of the substrate as well as the thickness of the substrate.
Breakdown Voltage:
For small active area devices, by definition breakdown voltage is defined as the voltage at which the dark current becomes 10µA. Since dark current increases with temperature, therefore, breakdown voltage decreases similarly with increase in temperature.
Responsivity:
Effects of temperature on responsivity is discussed in the “Responsivity” section of these notes.