Electrical properties and local structure ofn-type conducting amorphous indium sulphide

An n-type amorphous chalcogenide, In49S51, having a band gap of 1.9eV, has been found. The conductivity in as-prepared films was ∼10−4 S cm−1, which increased to 1 × 10−1 S cm−1 on post-annealing at 125°C in vacuum, accompanied by a reduction in the sulphur content of the films. TEM observations showed the amorphous nature of the films before and after annealing. Both Seebeck and Hall coefficients are negative, indicating that the major carriers are electrons. The Hall mobility can be as large as 26 cm2 V−1 s−1 at 300 K. No significant changes to the optical absorption were observed upon annealing. Analysis of the X-ray radial distribution function reveals that the sulphur atoms have four-fold coordination, making the structure more rigid than conventional amorphous chalcogenides in which the chalcogen is alloyed to elements of group IV or V of the periodic table. We tentatively associate the electron carrier generation with the formation of sulphur vacancies.