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Posted: Dec 15, 2014

High-performance phototransistor based on multilayer GaTe

(Nanowerk News) As an emerging class of new material, two-dimensional (2D) layered materials are attracting considerable interest in the past decade since graphene was discovered in 2004. In contrast to graphene, the presence of an inherent band gap allows 2D semiconductors to be highly promising building blocks for high-performance electronic and optoelectronic applications. Moreover, compared to traditional semiconductor materials, such as Si and III-V group materials, 2D layered semiconducting material exhibit three important features: the ultrathin thickness, smooth surface, and high compatibility with flexible devices.
Gallium telluride (GaTe) is an important III-VI layered semiconducting material. Better than most transition metal dichalcogenides, such as MoS2 and WSe2, GaTe has a direct band gap of around 1.7 eV in both single layer and bulk form at room temperature. This implies GaTe may have excellent optoelectronic properties even in its multilayer state. However, due to the challenges from complicated and less symmetric monoclinic crystal structure, GaTe is not well studied.
In addition, for most metal chalcogenide semiconductors, ion vacancies (cation or anion) play a crucial role in their electrical properties. These defects should have strong influences on the electrical properties of these materials. However, how these defects affect the device performance is not systematically studied and the physical mechanism is still unclear. Understanding the origin of device performance deterioration will be helpful to find a way to restore, even enhance the device performance based on these materials.
In the work coming out of the Jun He group at National Center for Nanoscience and Technology of China, researchers find Ga ion vacancy is the critical factor that causes the high off-state current, low on/off ratio of GaTe FET and large hysteresis at room temperature through electrical transport measurements at variable temperatures and first-principles calculations as well. By suppressing thermally activated Ga vacancy defects at liquid nitrogen temperature, the FET properties have been significantly enhanced. A GaTe nanosheet FET with on/off ratio ~105, off-state current ~10-12 A and negligible gate hysteresis is successfully demonstrated.
These results have been published in ACS Nano ("Role of Ga Vacancy on a Multilayer GaTe Phototransistor"). The findings are of scientific importance to understand the physical nature of intrinsic GaTe transisotor performance degradation and also technical significance to unlock the hurdle for practical applications of GaTe transisotors in the future.
Source: National Center for Nanoscience and Technology
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