J12 Series detectors are high-quality Indium Arsenide photodiodes for use in the 1 to 3.8 µm wavelength range. The equivalent circuit is a photon-generated current source Iph with parallel capacitance Cd, shunt resistance Rd, and series resistance Rs (Fig. 1). The output signal current Is is defined as:
Is = Iph Rd/Rd + Rs + Rload
Rd varies as a function of detector temperature (Fig. 2). Rs depends on the position of the source light spot on the detector surface; it varies with the distance from the spot to the detector contact ring . When Rs is small compared to Rd it may be disregarded, but with room temperature InAs the effects of Rs are significant.
