Photo-Seebeck measurement of Bi-doped amorphous germanium telluride oxide film

Seebeck measurements of n-type amorphous germanium telluride thin films (100 nm) containing oxygen and implanted with Bismuth (Bi) have been studied under dark and monochromatic light conditions from 1800 to 400 nm. The Bi-doped film has a negative Seebeck coefficient indicating its n-type nature that results from the implantation compared to the p-type undoped films. Upon illumination with monochromatic light across the near-infrared and visible region the magnitude of the measured Seebeck voltage increases (becomes more negative). This increase in Seebeck coefficient displays distinctive behaviours in different spectral regions and is caused by the inclusion of Bi ions as foreign impurities. Furthermore, the Seebeck coefficients are used to determine the film electrical properties and enable, along with complementary characterisation including X-ray photoelectron spectroscopy, electronic band diagrams to be proposed for before and after Bi ion implantation. The photo-Seebeck technique is utilised for the first time to probe the trap states created due to the implantation, providing an understanding of the mechanisms behind non-equilibrium carrier-type reversal in an amorphous system, including the modification of electronic and optoelectronic properties such as the optical bandgap.