# Electron Transport in \(n\)-Type InSe van der Waals Crystals with Co Impurities
###### Abstract  
Intercalation and doping are promising routes to tune properties of van der Waals (vdW) semiconductors and pave the way for their applications in digital electronics beyond Moore's law, sensors and spintronics. The indium selenide (InSe) vdW crystal shows great promise for use in next-generation semiconductor technologies. For these applications to be realized, the effects of impurities on properties of InSe must be understood. Here, we present a comparative experimental study of electron transport in \(n\)-type InSe semiconductor doped and electrochemically intercalated with magnetic cobalt (Co) impurities. It is shown that the presence of Co decreases the free electron density, the Hall mobility along layers and the conductivity anisotropy \(\sigma_{\perp\mathrm{C}}/\sigma_{\parallel\mathrm{C}}\). Furthermore, this leads to a change of the behavior of \(\sigma_{\perp\mathrm{C}}(T)\) dependence from a metallic one in pristine samples to a semiconducting one in samples with Co. We also demonstrate that the interaction of electrons with space-charge regions is an effective scattering mechanism, which should be taken into account in doped and intercalated crystals. The present work is important for the basic physics knowledge of the effect of Co impurities on physical properties of InSe, which is needed to tailor the parameters of this semiconductor for applications in electronics and spintronics. InSe; electron transport; semiconductors; van der Waals crystals; intercalation; doping; cobalt; magnetic impurities +
Footnote †: journal: Applied Sciences  
materials that integrate both semiconducting and magnetic properties within the same crystal. To date, the integration of magnetic properties within a semiconductor crystal has proven to be challenging. Attempts to create magnetic semiconductors have often led to a significant deterioration of the crystal quality, but also led to material systems with new interesting magnetic and electronic properties. The majority of layered van der Waals materials, including InSe, are nonmagnetic in the pristine form, which restricts their application in spintronic devices, and controlling their magnetism still remains an open question [14]. The integration of magnetic properties within a semiconductor van der Waals crystal is generally challenging to achieve. This integration is important for several applications and new device concepts in spintronics, including electrical control of the magnetization and generation of spin-currents, spin-filtering and spin-amplification in logic devices. To date, the realization of magnetic semiconductors has proven to be challenging, but it has a great potential to lead to material systems with interesting magnetic and electronic properties. There are many ways to introduce magnetism in such layered materials, for instance by using dopants, vacancies, elastic deformations and absorption of molecules [15]. In contrast to conventional covalently bonded materials, the properties of van der Waals crystals can be changed by one more method, namely intercalation [16]. The absence of dangling bonds within separate layers of III-VI crystals and a significant spacing between them (3:4 A) enable modification of properties of as-grown crystals by inserting guest species, such as atoms, ions or molecules, into empty van der Waals gaps. Their number can be compared and even exceed that of the basic compound. Intercalation technology enables creation of new composite material systems in which there is a nanoscale alternation of semiconductor 2D layers and intercalant interlayers, including those of magnetic substances. This has been explored in our earlier experiments on III-VI van der Waals compounds [17; 18; 19; 20; 21; 22]. This approach can be considered as one of the most promising for progress of spintronic devices based on van der Waals semiconductors. Previous attempts to obtain semi-magnetic van der Waals III-VI semiconductors reported in the literature usually involved adding magnetic dopants before synthesis [23; 24; 25; 26; 27; 28].