Hidden surface channel in two-dimensional multilayers

Abstract

Numerous carrier scatterers, such as atomic defects, fixed oxide charges, impurities, chemical residues, and undesired surface adsorbates, including oxygen and water molecules, strongly degrade the carrier mobility of atomically thin two-dimensional (2D) materials. However, the effect of surface adsorbates and surface oxidation on the carrier density profile along the thickness of 2D multilayers is not well known, particularly for a substantial interruption in the formation of the top-surface channel. Here, we uncover a hidden surface channel in p-type black phosphorus and n-type rhenium disulfide multilayers originating from undesired ambient adsorbates and surface oxides that not only populate hole density (or reduce electron density) but also suppress carrier mobility. The absence of a second peak in the transconductance curve under ambient conditions indicates the disappearance of the top-surface channel inside the 2D multilayers, which is a possible indicator for the cleanliness of the top surface and can be used in gas sensor applications. Moreover, the negligible variation in the drain bias polarity-dependent turn-on voltage for the bottom channel under ambient conditions validates the exclusive contribution of surface adsorbates to the formation of the top channel in 2D multilayers. Our results provide a novel insight into the distinct carrier transport in 2D optoelectronic devices and diverse sensors.

High Temperature Carrier Scattering Mechanisms in Multilayer ReS2 Field-Effect Transistors

“…The observed dominant E g (≈ 150−160 cm −1 ), A 1g -like (≈ 215 cm −1 ) and E g -like (≈ 312 cm −1 ) peaks are consistent with those obtained in previous reports, and clearly indicate the presence of a ReS 2 multilayer, as shown in Fig. 1(c) [7,9,11,12]. All electrical measurements were conducted using a commercial semiconductor analyzer (B1500A Keysight).…”

“…2(a) and 2(b). A clear linearity regardless of V G is presented in these figures at small V D regimes (< 0.5 V), which indicate negligible Au-ReS 2 Schottky barrier (SB) effects [9,11,13]. However, a non-monotonic behavior gradually appears after V D exceeds 1 V. This distinct behavior has been mainly ascribed to the suppressed R IT and/or enhanced carrier mobility effects on conducting channel migration in the ReS 2 multilayers [10,14].…”

“…The fabricated device was thermally annealed for 10 h at 200 ∘ C under a high vacuum of less than 10 −6 Torr. The detailed fabrication method employed in this study is described in the literature [9][10][11]. The optical Raman spectrum of 11 nm-thick ReS 2 was obtained using a laser excitation wavelength (𝜆 EX ) with a laser power (P) of 5 mW.…”

“…4, the employed Matthiessen's rule appropriately describes the V Ddependent 𝜇 FE for T ≤ 380 K. In this temperature regime, the dominant scattering mechanism varies from 𝜇 C to 𝜇 Ph , mainly because of conducting channel migration with increasing V D . Since the SiO 2 used in this study consists of numerous positive fixed trap sites near the bottom surface of the proposed ReS 2 structure, 𝜇 C should dominate 𝜇 FE when the channel centroid is located near dielectrics[1,11,21]. However, as the channel centroid shifts upward to minimize the R IT contribution to carrier transport with increasing V D , the effect on 𝜇 FE of 𝜇 C (or 𝜇 Ph ) becomes weaker (or stronger), resulting in a sign reversal of the temperature exponent of 𝜇 FE , ranging from −0.4 to 1.2.At T ≥ 380 K, the general trend of Matthiessen's rule fails to explain the T-dependent 𝜇 FE , mainly because of the largely enhanced 𝜇 FE at high temperatures, as shown in Fig.3(d).…”

2D Rhenium Dichalcogenides: From Fundamental Properties to Recent Advances in Photodetector Technology

“…From a device perspective, more studies on the electrical behavior of these materials in field‐effect transistor device configuration, under various dielectric and passivation environments, are needed as phototransistor remains the most common device platform for sensing the light. This later necessity also comes from recent demonstration of hidden surface channel [ 370 ] and restricted channel migration [ 371 ] in multilayer ReS 2 transistors. The broadband optical anisotropy in these layered systems shows their incredible potential for the design of miniaturized spectrometers and active control of polarization‐sensitive photonic devices.…”