N‐Doped Graphene Field‐Effect Transistors with Enhanced Electron Mobility and Air‐Stability

Although graphene can be easily p‐doped by various adsorbates, developing stable n‐doped graphene that is very useful for practical device applications is a difficult challenge. We investigated the doping effect of solution‐processed (4‐(1,3‐dimethyl‐2,3‐dihydro‐1H‐benzoimidazol‐2‐yl)phenyl)dimethylamine (N‐DMBI) on chemical‐vapor‐deposited (CVD) graphene. Strong n‐type doping is confirmed by Raman spectroscopy and the electrical transport characteristics of graphene field‐effect transistors. The strong n‐type doping effect shifts the Dirac point to around ‐140 V. Appropriate annealing at a low temperature of 80 ºC enables an enhanced electron mobility of 1150 cm² V^?1 s^?1. The work function and its uniformity on a large scale (1.2 mm × 1.2 mm) of the doped surface are evaluated using ultraviolet photoelectron spectroscopy and Kelvin probe mapping. Stable electrical properties are observed in a device aged in air for more than one month.     

25th Anniversary Article: Recent Advances in n‐Type and Ambipolar Organic Field‐Effect Transistors

The advantages of organic field‐effect transistors, such as low cost, mechanical flexibility and large‐area fabrication, make them potentially useful for electronic applications such as flexible switching backplanes for video displays, radio frequency identifications and so on. A large amount of molecules were designed and synthesized for electron transporting (n‐type) and ambipolar organic semiconductors with improved performance and stability. In this review, we focus on the advances in performance and molecular design of n‐type and ambipolar semiconductors reported in the past few years.     

Free‐Standing 2D Hexagonal Aluminum Nitride Dielectric Crystals for High‐Performance Organic Field‐Effect Transistors

The existence of defects and traps in a transistor plays an adverse role on efficient charge transport. In response to this challenge, extensive research has been conducted on semiconductor crystalline materials in the past decades. However, the development of dielectric crystals for transistors is still in its infancy due to the lack of appropriate dielectric crystalline materials and, most importantly, the crystal morphology required by the gate dielectric layer, which is also crucial for the construction of high‐performance transistor as it can greatly improve the interfacial quality of carrier transport path. Here, a new type of dielectric crystal of hexagonal aluminum nitride (AlN) with the desired 2D morphology of combing thin thickness with large lateral dimension is synthesized. Such a suitable morphology in combination with the outstanding dielectric properties of AlN makes it promising as a gate dielectric for transistors. Furthermore, ultrathin 2,6‐diphenylanthracene molecular crystals with only a few molecular layers can be prepared on AlN crystal via van der Waals epitaxy. As a result, this all‐crystalline system incorporating dielectric and semiconductor crystals greatly enhances the overall performance of a transistor, indicating the importance of minimizing defects and preparing high‐quality semiconductor/dielectric interface in a transistor configuration.