High Performance n-type Black Phosphorus Transistors with Self-Encapsulated Photoactive Doping Layers
Date Issued
2015
Date
2015
Author(s)
Li, Min-Ken
Abstract
Black phosphorus, the most stable allotrope of phosphorus, is a layered material and each atomic layer is held together by weak van der Waals interactions, which is similar to graphite. Other than graphene, black phosphorus is the second known two-dimensional material which is formed by a single element. Recently, exfoliated few-layer black phosphorus, also named as phosphorene, has drawn great interest because of its innovative optical and electrical properties. Its high hole mobility (intrinsic p-type semiconductor) up to ~1000 cm2V-1s-1, high current on/off ratio of ~105, thickness-tunable direct bandgap, anisotropy, and so on make black phosphorus a promising candidate in the future two-dimensional transistors, optoelectronic devices, and logic devices. However, few-layer black phosphorus has also been widely investigated for its instability upon exposure to ambient condition. The quality of phosphorene in many respects, such as carrier mobility and current on/off ratio gradually deteriorate when exposed to ambient air. Phosphorene would even totally disintegrate in the long run and its further researches and applications are then severely restricted. In this regard, suitable passivation techniques for black phosphorus to enhance the stability have turned into an urgent issue. In the first part of this work (chapter 4), we introduced a novel passivation approach by covering few-layer black phosphorus with self-encapsulated, ultra-thin film titanium suboxide (TiOx) which is low-cost and solution-processable. With the passivation of ultra-thin film TiOx which is merely a few nanometers on phosphorene, the unstable nature of black phosphorus under ambient condition can be significantly improved. Besides, black phosphorus is well known as an intrinsic p-type semiconductor. Thus, to obtain a high performance n-type black phosphorus transistor would be more difficult than its p-type counterpart. In the second part of this work (chapter 5), we integrated the innovative characteristics of TiOx with black phosphorus transistors. In fact, TiOx has been well studied as passivation layer, charge transport layer, and even light-sensitized n-type dopant in organic electronics or graphene-based transistors. With these properties, we not only solved the instability problem of black phosphorus but also successfully demonstrated a high performance and precisely controllable n-type black phosphorus transistor at the same time, which can be of great impact for developing practical complementary metal–oxide–semiconductor devices based on black phosphorus.
Subjects
black phosphorus
TiOx
stability
photoactive
n-type doping
Type
thesis
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