## 3 Results and Discussion
### Transport Properties along the Layers
According to the literature [31; 32; 33], extrema in \(R_{\text{H}}(T)\) dependences were observed in many compounds and were explained by a simultaneous contribution to the conductivity of the carriers from a main band and an impurity band, which is separated from it, with essentially different mobilities. However, the apparent mobility values are too high to be attributed to an impurity band, which is evidence against such an explanation in our case. A mixed conductivity of the samples under investigation could also be caused by light and heavy electrons in the conduction band. However, starting from band structure calculations for \(\gamma\)-InSe [34], a model of a complex conduction band should be rejected. The decrease of the Hall coefficient with decreasing temperature could also be explained as a tendency to change the conductivity type from \(n\) to \(p\). However, a self-compensation mechanism is inherent for \(n\)-InSe crystals--that is, adding acceptors leads to the appearance of new compensating donors. Besides, it is known that even if the impurities are acceptors within a layer, they act as donors in the interlayer positions [35]. Therefore, this explanation of the Hall coefficient behavior after the insertion of RbNO\({}_{3}\) is probably not correct. As we found earlier [36; 37; 38; 39], non-monotonic temperature dependences of \(R_{\text{H}}\) and \(\mu_{\perp C}\) in \(n\)-InSe irradiated with electrons can be explained assuming that electron transport along the layers is due to a contribution of high-mobility three-dimensional (3D) electrons and less-mobile two-dimensional (2D) ones. It is known that polytypism and vdW coupling between the InSe layers cause the presence of typical planar stacking faults between different structure polytypes, where impurities (dopants, intercalants, intrinsic atoms, residual impurities) can be accumulated. The presence of degenerate 2D accumulating layers is ascribed to planar inclusions of charged donor impurities at such stacking faults. Their electrical potential bends the c-band bottom, creating energy wells across the layers. In such energy sub-bands, electrons behave as a degenerate 2D electron gas--that is, they keep free motion along the layers but are restricted to move across them. The apparent temperature dependences of the Hall coefficient and mobility for the intercalated samples can also be interpreted within the model that takes into account the contributions of 3D and 2D electrons to the transport of charge carriers along the layers. One can assume that 2D carriers largely determine the transport properties at low temperatures. With increasing temperature, the 2D carriers become thermally activated in the main bulk of \(n\)-InSe and the dimensionality of electron transport changes. If we assume that, according to [40], the dependence of the mobility ratio \(b=\mu_{3}/\mu_{2}\) on temperature is much weaker than that on the concentration ratio of 3D and 2D electrons \(x=n_{3}/n_{2}\), then in the maximum point of the Hall coefficient the equation  
\[R_{max}/R_{dep}=\left(b+1\right)^{2}/4b \tag{4}\]  
is correct. Here, \(R_{max}\) is the value of the parameter at the depletion of carriers when \(n_{dep}=n_{2}+n_{3}=\text{const}\). Knowing the value of \(b\), one can determine from the experimental data the values of \(n_{2}\) and \(n_{3}\) as a function of temperature using expression (3). For the intercalated sample 3, calculations were not done because it is impossible to determine \(n_{\text{dep}}\), but for sample 2 at \(r_{2}=r_{3}=1\) and \(n_{\text{dep}}=2.08\cdot 10^{15}\) cm\({}^{-3}\) the temperature dependences of the concentrations are shown in Figure 4.  
Further analysis of the \(n_{3}(T)\) dependence was carried out within a \"single donor-single acceptor\" model considering that \(N_{D}-N_{A}=n_{\text{dep}}\).