Electric Double Layer Field-Effect Transistors Using Two-Dimensional (2D) Layers of Copper Indium Selenide (CuIn7Se11)

Abstract

Innovations in the design of field-effect transistor (FET) devices will be the key to future application development related to ultrathin and low-power device technologies. In order to boost the current semiconductor device industry, new device architectures based on novel materials and system need to be envisioned. Here we report the fabrication of electric double layer field-effect transistors (EDL-FET) with two-dimensional (2D) layers of copper indium selenide (CuIn 7 Se 11 ) as the channel material and an ionic liquid electrolyte (1-Butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF 6 )) as the gate terminal. We found one order of magnitude improvement in the on-off ratio, a five-to six-times increase in the field-effect mobility, and two orders of magnitude in the improvement in the subthreshold swing for ionic liquid gated devices as compared to silicon dioxide (SiO 2 ) back gates. We also show that the performance of EDL-FETs can be enhanced by operating them under dual (top and back) gate conditions. Our investigations suggest that the performance of CuIn 7 Se 11 FETs can be significantly improved when BMIM-PF 6 is used as a top gate material (in both single and dual gate geometry) instead of the conventional dielectric layer of the SiO 2 gate. These investigations show the potential of 2D material-based EDL-FETs in developing active components of future electronics needed for low-power applications.Electronics 2019, 8, 645 2 of 12 chips. High-κ dielectric materials, such as inorganic, polymer, and electrolyte dielectrics, have been incorporated into FETs depending on cost, durability, operation speed, and transconductance for better performance of FETs, as well as potential applications in flexible and stretchable electronics [4,5]. In this regard, ionic liquids have emerged as promising dielectric gate materials in FETs [6][7][8]. Electric double layers (EDL) formed by ionic liquid result in higher capacitance due to their atomically thin charge layer. The charge accumulated (Q) by a capacitor is given by Q = C × V, where C is the capacitance and V is the applied voltage. The higher capacitance in the EDL yield in higher electrostatic charge carrier doping in the semiconductor channel ultimately results in high on-state current and lower threshold and operational voltages. Further, it has been shown through other different applications, such as batteries, capacitors, fuel cells, solar cells, and actuators, that ionic liquids have exceptional and stable chemical properties [8][9][10][11][12].Recently, ionic liquids have been integrated with two-dimensional (2D) material-based FETs, which has resulted in various fascinating applications [13][14][15][16][17][18][19][20]. For example, studies have indicated that superconductivity can be induced in atomically thin layers of ZrNCl-based FETs at T = 15.2 K by using ionic liquid DEME-TFSI as the gate [13], ambipolar metal-insulator transition can be induced in thin flakes of black phosphorus-based FETs with DEME-TFSI as the gate dielectric [14], and ferroma...

Gate-Induced Metal–Insulator Transition in 2D van der Waals Layers of Copper Indium Selenide Based Field-Effect Transistors

“…As grown CIS crystal has black mica-like texture. Layered CIS has been characterized by SEM, HRTEM, EDX, and XRD. − The ratio between copper and indium has been found to be 1:7, which is consistent with layered-phase formation in CIS (CuIn 7 Se 11 ).…”

“…Multielemental compounds bring an extra degree of freedom via stoichiometric variations, and varying elemental composition could play an important role in determining physical properties. , For example, our own investigations suggest that incorporating copper in indium selenide (InSe) in order to get layered ternary systems of copper indium selenide (CuIn 7 Se 11 ) and using them as the active component for photodetection can substantially improve a photodector’s figures of merit (for example, response time) . Despite the fact that CIS-based systems show excellent electronic , and optoelectronic , properties, electron transport in these systems is not well understood. In order to further engineer their properties for various device applications, it is crucial to understand the nature of electron transport in these materials.…”

Epitaxial Growth of 2D Ternary Copper–Indium–Selenide Nanoflakes for High‐Performance Near‐Infrared Photodetectors

“…At a fixed source–drain voltage ( V DS ) of 3 V, source–drain currents ( I DS ) first slightly decreased and then increased when gate voltages ( V G ) increased from −50 to 50 V. This showed that the CIS nanoflakes exhibited n‐type semiconductive behavior and good switching characteristics with an approximate on/off ratio of 10 9 , which was much higher than that of CuIn 7 Se 11 and better or comparable with those of other as‐grown 2D materials. [ 28,42–46 ] Because graphene exhibits metallic behavior, the field effect mobility of the CIS nanoflakes can be calculated through the transfer curves of the devices according to the following equation: where L and W are the channel length and width of the device, ε (= 8.85 × 10 −12 F m −1 ) is the vacuum permittivity, ε r (= 3.9) is relative permittivity of the insulating barrier SiO 2 , and d (= 300 nm) is the thickness of SiO 2 . The field effect mobility of the CIS nanoflakes was estimated to be 30.4 cm 2 V −1 s −1 , which was comparable with that of mechanically exfoliated CuIn 7 Se 11 .…”

“…−50 to 50 V. This showed that the CIS nanoflakes exhibited n-type semiconductive behavior and good switching characteristics with an approximate on/off ratio of 10 9 , which was much higher than that of CuIn 7 Se 11 and better or comparable with those of other as-grown 2D materials. [28,[42][43][44][45][46] Because graphene exhibits metallic behavior, the field effect mobility of the CIS nanoflakes can be calculated through the transfer curves of the devices according to the following equation:…”

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

“…With the advent of layered Van der Waals solids [1][2][3] and the envisioned applications that are being expected [4][5][6][7][8][9][10][11][12][13] has led to a large variety of fundamental as well as applied scientific investigations. Among these investigations, many have shown that intrinsic properties of 2D layered materials are strongly dependent on the number of layers [8,[14][15][16].…”