Impact of the Coulomb interaction on the Franz-Keldysh effect in high-current photodetectors.

The Franz-Keldysh effect has been recognized as the largest contributor to oscillations in the responsivity of high-current photodetectors as a function of the applied bias or the incident light wavelength and to device nonlinearity. Prior work only considered the effect of the electric field without considering the Coulomb interaction. We show that it is not possible to obtain agreement with experiments at all optical wavelengths without including this effect in the effective mass equation. We find the maxima and minima in the absorption of the applied electric field shift when the Coulomb interaction is included. We then use the calculated absorption with the drift-diffusion equations to calculate the responsivity in a partially depleted absorber (PDA) photodetector, and we obtain excellent agreement with experiments at all biases and optical wavelengths.