Thermal noise that occurs in resistors. The rms noise voltage of a resistor is given by √(4 kTRB) where is Boltzmann's constant, is the abolute temperature, is the resistance and is the bandwidth in Hertz.
When operated in the PV mode at 0 volt bias, a photodiode will generate Johnson noise current due to its shunt resistance (RD) according to: i2 = 4KT f / RD where K is the Boltzman constant, T is temperature in °K, f is the noise measurement bandwidth and RD is the detector shunt resistance. Junction Capacitance (CD) The p-n junction of a photovoltaic detector has a capacitance proportional to the active size.