Combined electrical transport and capacitance spectroscopy of a MoS2-LiNbO3 field effect transistor

Abstract

We have measured both the current-voltage (I SD -V GS ) and capacitance-voltage (C-V GS ) characteristics of a MoS 2 − LiNbO 3 field effect transistor. From the measured capacitance we calculate the electron surface density and show that its gate voltage dependence follows the theoretical prediction resulting from the twodimensional free electron model. This model allows us to fit the measured I SD -V GS characteristics over the entire range of V GS . Combining this experimental result with the measured current-voltage characteristics, we determine the field effect mobility as a function of gate voltage. We show that for our device this improved combined approach yields significantly smaller values (more than a factor of 4) of the electron mobility than the conventional analysis of the current-voltage characteristics only.After the rise of graphene 1-3 , a wide range of twodimensional (2D) materials 4 shifted into focus of fundamental and applied research 5 . One particularly important class of 2D materials are transition metal dichalcogenides (TMDs) 6 . One important representative TMD is molybdenum disulfide, MoS 2 , whose indirect band gap changes to a direct one when its thickness is reduced to one single monolayer 7,8 . The resulting high optical activity and sizable bandgap of ∼ 1.9 eV make this material ideally suited for optoelectronic applications 9 and, thus the optical and electronic properties of MoS 2 and related materials have been investigated intensively in the last years 10 . In particular, field effect transistors (FETs) and logical circuit prototypes have been devised and realized [11][12][13] . In such devices, source and drain contacts are patterned onto the TMD film, and the charge carrier density is controlled by gate contacts. For FET devices, the transport mobility of the charge carriers in the conducting channel is of paramount importance. Here, different approaches exist to derive this key figure for FET devices. The most commonly applied method is to measure the source-drain current I SD as a function of the gate voltage V GS . Then, the field effect mobility µ FE is determined from a tangent to the linear region of the I SD (V GS )-dependence using the following formula known from FET theory:Here, C(V GS )/A is the capacitance per unit area, V SD the source-drain voltage, ∂ISD ∂VGS the slope of the linear a) Electronic region, L the length and w the width of the conducting channel. The intersection of the tangent with the abscissa represents the threshold voltage, V Th . However, this simple FET formula (1) assumes that the mobility is independent of the gate voltage. Moreover, the underlying parallel-plate capacitor model used to quantify the capacitance 11,14 assumes perfectly conducting, infinitely large plates. These assumptions may represent an oversimplification for 2D semiconductors 15,16 . To quantify the capacitance more precisely, Radisavljevic and coworkers 17 followed an indirect approach: the capacitance was determined from the carrier density obtained from Hall effect me...

Large Band Offset in Monolayer MoS2 on Oppositely Polarized BiFeO3(0001) Polar Surfaces

“…In recent years, many experimental efforts − have been focused on integrating 2D MX 2 materials with ferroelectrics due to their switchable electric polarization and the high dielectric constant. Hereinafter, we take MoS 2 as an example.…”

“…For chemical vapor deposition of MoS 2 onto LiNbO 3 (0001) polar surfaces, the polarization direction of the ferroelectric substrate showed a remarkable effect on the growth and transport properties of the MoS 2 films . As demonstrated in refs , , the monolayer MoS 2 /LiNbO 3 hybrid structure can be used for the field-effect transistor (FET) and the FET-electro-acoustic device. By transferring the MoS 2 flakes on top of the epitaxial PbZr 0.2 Ti 0.8 O 3 (PZT) single crystalline film, Lu et al reported that the back-gated MoS 2 /PZT FET shows excellent current–voltage behavior directly controlled by ferroelectric polarization.…”

Multi-harmonic quantum dot optomechanics in fused LiNbO3–(Al)GaAs hybrids

“…The transfer of the QDs onto a strong piezoelectric substrate such as LiNbO 3 , with K 2 » 5%, could help enhance the coupling between a semiconductor heterostructure and the SAW field [4]. However, direct epitaxial growth of semiconductors on LiNbO 3 has so far only be achieved for two-dimensional transition metal dichalcogenides [14,30]. Thus, for most semiconductors, such hybrid devices can be fabricated by epitaxial lift-off and transfer of the QD membrane on a LiNbO 3 SAW-chip [31][32][33][34][35][36][37].…”

Accumulation-Mode Two-Dimensional Field-Effect Transistor: Operation Mechanism and Thickness Scaling Rule

“…Experimentally, C-V measurements in small-area 2D materials are very sensitive and always suffer from several difficulties. 5,[38][39][40][41] A systematic study on the parasitic capacitance resulting from an n + -Si/SiO2 substrate and the channel resistance effect in C-V is necessary. Theoretically, quantum capacitance in monolayer MoS2 has been clarified in our previous work.…”

“…Although C – V measurements are quite informative, blindly applying this method established based on a bulk metal–oxide–semiconductor (MOS) FET/capacitor to an ACCU-FET can lead to incorrect conclusions. Experimentally, C – V measurements in small-area 2D materials are very sensitive and always suffer from several difficulties. ,− A systematic study on the parasitic capacitance resulting from an n + -Si/SiO 2 substrate and the channel resistance effect in C – V is necessary. Theoretically, quantum capacitance in monolayer MoS 2 has been clarified in our previous work .…”