Few-Layer GeAs Field-Effect Transistors and Infrared Photodetectors.

The family of 2D semiconductors (2DSCs) has grown rapidly since the first isolation of graphene. The emergence of each 2DSC material brings considerable excitement for its unique electrical, optical, and mechanical properties, which are often highly distinct from their 3D counterparts. To date, studies of 2DSC are majorly focused on group IV (e.g., graphene, silicene), group V (e.g., phosphorene), or group VIB compounds (transition metal dichalcogenides, TMD), and have inspired considerable effort in searching for novel 2DSCs. Here, the first electrical characterization of group IV-V compounds is presented by investigating few-layer GeAs field-effect transistors. With back-gate device geometry, p-type behaviors are observed at room temperature. Importantly, the hole carrier mobility is found to approach 100 cm2 V-1 s-1 with ON-OFF ratio over 105 , comparable well with state-of-the-art TMD devices. With the unique crystal structure the few-layer GeAs show highly anisotropic optical and electronic properties (anisotropic mobility ratio of 4.8). Furthermore, GeAs based transistor shows prominent and rapid photoresponse to 1.6 µm radiation with a photoresponsivity of 6 A W-1 and a rise and fall time of ≈3 ms. This study of group IV-V 2DSC materials greatly expands the 2D family, and can enable new opportunities in functional electronics and optoelectronics based on 2DSCs.