Features of the conduction mechanisms of the $n$-HfNiSn semiconductor heavily doped with the Co acceptor impurity

The crystalline structure, electron density distribution, energy and kinetic parameters of a HfNi$_{1-x}$Co$_x$Sn semiconductor heavily doped with a Co acceptor impurity are studied in the ranges $T$ = 80–1620 K and $N^{\mathrm{Co}}_A$ from 9.5 $\times$ 10$^{20}$ cm$^{-3}$ (at $x$ = 0.05) to 7.6 $\times$ 10$^{21}$ cm$^{-3}$ (at $x$ = 0.40). It is shown that variations in the activation energy of hopping conduction $\varepsilon^\rho_3(x)$ and the modulation amplitudes of continuous energy bands $\varepsilon^\alpha_1(x)$ are caused by the appearance of a donor source in the $n$-type HfNi$_{1-x}$Co$_x$Sn semiconductor. It is shown that the doping of $n$-HfNiSn with a Co acceptor impurity is accompanied by a change in the degree of compensation of the semiconductor due to the simultaneous generation of both structural acceptor-type defects during Ni atom substitution with Co atoms and structural donor-type defects during the partial occupation of Ni sites by Sn atoms. The results are discussed within the Shklovskii–Efros model for a heavily doped and compensated semiconductor.