Modulation of the two-photon absorption by electric fields in HgCdTe photodiode

We demonstrate the tunability of the two-photon absorption (TPA) coefficient by adjusting the electric field in a HgCdTe (MCT) photodiode with cutoff wavelength of 5.2μm. The TPA coefficient was measured by using a picosecond pulsed laser with wavelength of 7.92μm. An enhancement of the TPA coefficient occurs in the space charge region of the MCT pn junction, which can be attributed to the Franz–Keldysh effect induced by the built-in electric field. By applying a reverse bias to intensify the built-in field, the TPA coefficient is found to be further enhanced by a factor of 18.9. This electric field dependence of the TPA coefficient has been fairly interpreted by the pn junction model with the Franz–Keldysh effect included.