Effect of temperature on the current–voltage characteristics of GaAs/AlGaAs quantum cascade photodetectors

Transport of electrons within a quantum cascade photodetector structure takes place with the help of the scattering of electrons by phonons. By calculating scattering rates of the electrons mediated by longitudinal optical phonons (the dominant scattering mechanism), current–voltage characteristic of a quantum cascade photodetector is calculated. The results indicate that with the increase of bias voltage dark current increases rapidly, then the increase becomes slow at higher voltages, whilst photocurrent remains approximately constant with only slight variations in its magnitude. With the increase of temperature from 80 K to 160 K dark current increases by about two orders of magnitude while photocurrent varies slightly, so that at the illuminating power of 1 mW/m2 photocurrent density increases in mean from 1.10×10−9 A/cm2 at 80 K to 1.14×10−9 A/cm2 at 160 K and then decreases to 1.03×10−9 A/cm2 at 240 K. Thus the responsivity of the detector varies only slightly with temperature. However owing to the decrease in the resistivity of the photodetector with the increase of temperature, Johnson noise limited detectivity decreases considerably.