Photocurrent nonlinearity in GaAs/AlGaAs quantum cascade photodetectors

In this paper short circuit photocurrent nonlinearity in a quantum cascade photodetector as a function of illumination power density is studied theoretically. Theoretical modelling is based on the scattering of electrons by photons and longitudinal optical phonons. For this purpose electronic wavefunctions are calculated by using the Schrödinger equation in effective mass approximation. The results of calculations indicate that the short circuit photocurrent responsivity of the photodetector decreases very slightly with the increase of illumination power density, so that at the power density of 156 MW/m 2 the responsivity only decreases a few percent relative to the responsivity at 10 MW/m 2 . The decrease is smaller if the photodetector temperature is higher. In addition the responsivity of the photodetector is less sensitive to the value of illumination power density if the dopants densities in the active wells are lower. As the calculations indicate, the decrease in the short circuit photocurrent responsivity is due to the decrease of sheet density of electrons in the ground subbands of the active wells and the increase of the sheet density of electrons in the other subbands.