Quasilinear Kane conduction band model in nitrogen-doped indium tin oxide

The band nonparabolicity of indium tin oxide (ITO) polycrystalline thin films is investigated with the quasilinear Kane model through Seebeck and Hall effect measurements. We report Kane model nonparabolic band parameters of $m_0^{*}=0.21m_0$ and $C=0.52{\mathrm{eV}}^{\text{−}1}$ for ITO, in good agreement with historical photoemission, optical, and transport measurements. To do this, the ITO films were doped with nitrogen by ion implantation, with fluences ranging from $5\times {10}^{14}N{\mathrm{cm}}^{\text{−}2}$ to $5\times {10}^{15}N{\mathrm{cm}}^{\text{−}2}$. The presence of the nitrogen in the films was verified with x-ray photoelectron spectroscopy, and their acceptor character studied theoretically by density functional theory. Experimentally, the doped nitrogen formed ${N_O}^{\text{−}}$ defects, deep acceptor states that led to a controlled compensation in carrier concentration from $10.1\times {10}^{20}\pm 0.6\times {10}^{20}{\mathrm{cm}}^{\text{−}3}$ to $2.9\times {10}^{20}\pm 0.2\times {10}^{20}{\mathrm{cm}}^{\text{−}3}$. Understanding the band nonparabolicity of degenerately doped transparent conducting oxides is essential for their commercial application in solar cells, transparent thermoelectric generators, and transparent thin film transistors. In this work, the Seebeck and Hall effect approach with the quasilinear Kane model for band nonparabolicity is presented as a practical method by which to study the variation in carrier effective mass without reliance on optical measurements.