Large current modulation in exfoliated-graphene/MoS2/metal vertical heterostructures

Abstract

Graphene-based vertical field effect transistors have attracted considerable attention in the light of realizing high-speed switching devices; however, the functionality of such devices has been limited by either their small ON-OFF current ratios or ON current densities. We fabricate a graphene/MoS 2 /metal vertical heterostructure by using mechanical exfoliation and dry transfer of graphene and MoS 2 layers. The van der Waals interface between graphene and MoS 2 exhibits a Schottky barrier, thus enabling the possibility of well-defined current rectification. The height of the Schottky barrier can be strongly modulated by an external gate electric field owing to the small density of states of graphene. We obtain large current modulation exceeding 10 5 simultaneously with a large current density of ~10 4 A/cm 2 , thereby demonstrating the superior performance of the exfoliated-graphene/MoS 2 /metal vertical field effect transistor.a)

Electric field modulation of Schottky barrier height in graphene/MoSe2 van der Waals heterointerface

“…An ideality factor approaching unity suggests a high-quality vdW interface. We 5 demonstrated a large current ON-OFF ratio of >10 5 for a device for which N = 44, where the current ON-OFF ratio is defined as (ON-state current)/(OFF-state current) at V B = +0.5 V. This value is comparable to the highest ON-OFF ratio achieved in a graphene/MoS 2 /Ti vertical field-effect transistor [4]. The behavior is notably different in a device using a thinner or thicker MoSe 2 , as shown in Figs.…”

“…Note that a similar thickness dependence whereby the ON-OFF ratio is lower for a thinner TMD layer in a vertical heterostructure has been reported for graphene/MoS 2 /metal vertical heterostructures [3,4,18]. Thus, these behaviors are normal …”

“…Such materials include graphene, black phosphorous, transition metal dichalcogenides (TMD), and hexagonal boron nitride. Among these materials, heterostructures based on graphene and TMD have been found to exhibit functions that were previously not possible, including those of a vertical field-effect transistor [2][3][4][5], photocurrent generation [6,7], a spin-orbit proximity effect [8], and the ability to fabricate flexible devices [9]. Particularly, vertical field-effect transistors based on graphene/MoS 2 /metal heterostructures have been the subject of considerable attention mainly due to their large current ON-OFF ratio (10 3 to 10 5 ) combined with a large ON current density (>10 3 A/cm 2 ) [3,4].…”

“…Therefore, the graphene/MoSe 2 vdW interface acts as a Schottky diode with a gate-tunable barrier height. Therefore, the device acts as a vertical field-effect transistor [3,4] A series of devices with different N were fabricated and the values of φ min and φ max were obtained as summarized in Fig. 4(a).…”

Gate-Tunable WSe2/SnSe2 Backward Diode with Ultrahigh-Reverse Rectification Ratio

“…heterostructures have been recently investigated for different device applications such as transistors [9][10][11][12] , photodetectors 13,14 , photovoltaics 15,16 and LEDs 17,18 .…”