Features of the band structure and conduction mechanisms in the $n$-HfNiSn semiconductor heavily doped with Ru

The crystal and electronic structure and energy and kinetic properties of the $n$-HfNiSn semiconductor heavily doped with a Ru acceptor impurity are investigated in the temperature and Ru concentration ranges $T$ = 80–400 K and $N_A^{\mathrm{Ru}}\approx$ 9.5 $\times$ 10$^{19}$–5.7 $\times$ 10$^{20}$ cm$^{-3}$ ($x$ = 0–0.03), respectively. The mechanism of structural-defect generation is established, which changes the band gap and degree of compensation of the semiconductor and consists in the simultaneous concentration reduction and elimination of donor structural defects by means of the displacement of $\sim$1% of Ni atoms from the Hf (4$a$) positions, the generation of acceptor structural defects upon the substitution of Ru atoms for Ni atoms in the 4$c$ positions, and the generation of donor defects in the form of vacancies in the Sn (4$b$) positions. The calculated electronic structure of HfNi$_{1-x}$Ru$_x$Sn is consistent with the experiment. The results obtained are discussed within the Shklovsky–Efros model for a heavily doped and compensated semiconductor.