Abstract
Enhancing the device performance of single crystal organic field effect transistors (OFETs) requires both optimized engineering of efficient injection of the carriers through the contact and improvement of the dielectric interface for reduction of traps and scattering centers. Since the accumulation and flow of charge carriers in operating organic FETs takes place in the first few layers of the semiconductor next to the dielectric, the mobility can be easily degraded by surface roughness, charge traps, and foreign molecules at the interface. Here, a novel structure for high‐performance rubrene OFETs is demonstrated that uses graphene and hexagonal boron nitride (hBN) as the contacting electrodes and gate dielectric layer, respectively. These hetero‐stacked OFETs are fabricated by lithography‐free dry‐transfer method that allows the transfer of graphene and hBN on top of an organic single crystal, forming atomically sharp interfaces and efficient charge carrier‐injection electrodes without damage or contamination. The resulting heterostructured OFETs exhibit both high mobility and low operating gate voltage, opening up new strategy to make high‐performance OFETs and great potential for flexible electronics.
Highlights
The performance of organic field effect transistors (OFETs) is often constrained by the carrier channel mobility limited by the dielectric-semiconductor interface.[1,2,3,4,5] In particular, trap states, which can be induced by residual charge density in the dielectric or active layer, influence the threshold voltage, mobility, and hysteresis of transfer characteristics
We demonstrate a novel structure of high performance OFETs by stacking rubrene single crystal, graphene, and hexagonal boron nitride (hBN), which were employed as channel, electrode, and dielectric, respectively
We used rod-like rubrene crystals for OFET devices so that all the devices used in this work have b-axis of rubrene as a channel direction, which has been known as the highest mobility direction of rubrene.[18]
Summary
The performance of OFETs is often constrained by the carrier channel mobility limited by the dielectric-semiconductor interface.[1,2,3,4,5] In particular, trap states, which can be induced by residual charge density in the dielectric or active layer, influence the threshold voltage, mobility, and hysteresis of transfer characteristics. Rubrene single crystal FETs with air-gap dielectric and Au electrodes (Figire S5a) showed high mobility of 13 ~ 20 cm2/Vs as reported by other groups.[10, 30,31] When different electrodes such as evaporated thin gold (20 nm, Figure S5b) or exfoliated FLG (Figure S5c) were used in bottom gate-bottom contact (BG-BC) device configuration with hBN dielectric, the mobility (3 ~ 4 cm2/Vs) was lower than that of the devices with CVDSLG electrodes Using CVDSLG and hBN as contacts and dielectric in a BG-BC device (Figure S5d) resulted in high mobility similar to that of TG-TC devices, but with high operating voltage
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