Influence of channel thickness on charge transport behavior of multi-layer indium selenide (InSe) field-effect transistors

Abstract

Atomically thin Van der Waals solids that exhibit direct band gap in their few layer form can substantially impact the field of two dimensional (2D) materials based electronic devices and related applications. Here we report on electronic charge transport behavior of multi layer ntype InSe field-effect transistor (FET) devices fabricated on SiO 2 /Si substrate with seven different channel thicknesses, t > 20 nm, well within its direct band gap regime. Through gate dependent conductivity measurements over a wide range of temperatures (T; 20 K <T < 310 K), we show that, irrespective of the channel thickness, carrier transport in these materials occurs via Arrhenius-type activated process above a certain characteristic temperature (T * ), whereas for temperatures T < T * conduction occurs via variable range hopping (VRH) mechanism consistent with Mott's 2D VRH formalism, manifesting the presence of disorder induced localized states in these channels. Although the broad mechanisms of charge transport in all these devices are similar, the variation of correlation energy value (T 1 ) of VRH with channel thickness indicates fewer density of localized states in thinner channels and hence higher electron mobility even without sufficient charge impurity screening from the substrate. Such intricate interplay between channel thickness and charge impurity screening and its influence on overall disorder landscape and hence on carrier localization in 2D layered systems underscores the need for strategic optimization of device parameters for their future prospect in electronic applications.

Role of layer thickness and field-effect mobility on photoresponsivity of indium selenide (InSe)-based phototransistors

“…Detailed analysis and mechanisms of electronic transport in these devices are mentioned elsewhere [20]. Room temperature transfer characteristics curve is shown in Figure 2(d).…”

“…As mentioned earlier, layer thickness plays an important role in electrical/opto-electronic transport properties of 2D Van der Waals materials. It has been shown that mobility varies as thickness changes [20,34]. Also, the underlying substrate plays an import role in opto-electronic transport as charge traps states are primarily originate from underlying substrate [18,35].…”

“…Also, the underlying substrate plays an import role in opto-electronic transport as charge traps states are primarily originate from underlying substrate [18,35]. Effect of substrate is screened in thicker channel devices [20]. Thickness dependent studies are particularly important in optoelectronic devices as absorption of light could vary in thinner samples [36].…”

“…Such effect on the intrinsic properties due to simple addition of layers also influences functional properties of devices such as field-effect transistors (FETs) [17,18]. For example, in FETs fabricated using MoS2 [17,19] and InSe [20,21], the field-effect mobility (FE) shows as inverse relationship with material thickness. Similarly, these studies also indicate that on/off ratios decrease drastically with increasing layer thickness.…”

Broadband Photocurrent Spectroscopy and Temperature Dependence of Band-gap of Few-Layer Indium Selenide

“…The detail device fabrication method and electrical transport characterization are presented in one of our previous publications [22,23]. In short the devices were fabricated on Silicon/Silicon dioxide (SiO 2 ) wafers with a (SiO 2 ) thickness of 1000 nm.…”