Structural defect generation and band-structure features in the HfNi$_{1-x}$Co$_x$Sn semiconductor

The crystal and electronic structure and magnetic, energy, and kinetic properties of the $n$-HfNiSn semiconductor heavily doped with the Co acceptor impurity (HfNi$_{1-x}$Co$_x$Sn) are investigated in the temperature and Co concentration ranges $T$ = 80–400 K and $N^{\mathrm{Co}}_A\approx$ 9.5 $\cdot$ 10$^{19}$–5.7 $\cdot$ 10$^{21}$ cm$^{-3}$ ($x$ = 0.005–0.30), respectively, and under magnetic field $H\le$ 10 kOe. It is established that the degree of compensation of the semiconductor changes due to transformation of the crystal structure upon doping, which leads to the generation of acceptor and donor structural defects. The calculated electronic structure is consistent with the experiment; the HfNi$_{1-x}$Co$_x$Sn semiconductor is shown to be a promising thermoelectric material. The results obtained are discussed within the Shklovsky–Efros model for a heavily doped and compensated semiconductor.