Low field transport calculations in TiS3 using ab-initio methods
Avinash Kumar, .
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Titanium Trisulfide (TiS3) is an attractive material with novel electronic properties. It has a bandgap similar to silicon and predicted high electron mobility. We carry out first principles calculations on TiS3 in order to explain the experimentally observed electronic structure and transport properties. We show that low field electron mobility is limited by the optical phonon scattering mechanism, which explains the large discrepancy between experimentally measured mobility and calculated mobility in previous reports. First, ab-initio calculations are performed on a monoclinic TiS3 lattice, based on density functional theory (DFT) framework, from which the density of states, effective masses of electrons and holes in the x, y and z cartesian directions, are calculated and the hole masses are compared with experimental data. Then, using density functional perturbation theory (DFPT) and recently developed ab-initio based electron phonon interaction theory, we calculate the electron-phonon interaction elements which is used in Fermi's Golden rule to get the scattering rate. The calculated rates are then used to solve the Boltzmann transport equation (BTE) to obtain the anisotropic mobilities and compared with experiments. The group symmetry shows 9 IR (Infrared) active modes which are expected to contribute scattering in TiS3. Low-field mobility is calculated taking into account the polar optical phonon scattering as well as ionized impurity scattering and compared with experimental data. A separate calculation is performed to include the effects of the polar nature of the optical phonon modes. Using the parameters obtained, we also performed a 3D device simulation on two different gate length devices, using Silvaco ATLAS TCAD tool to match experimentally observed current-voltage characteristics.