Two dimensional III-VI semiconductors and graphene-hybrid heterostructures

The isolation of single-atomic layer graphene has led to a surge of interest in other layered crystals with strong in-plane bonds and weak, van der Waals-like, interlayer coupling. A variety of two-dimensional (2D) crystals have been investigated, including large band gap insulators and semiconductors with smaller band gaps such as transition metal dichalcogenides. Interest in these systems is motivated partly by the need to combine them with graphene to create field effect transistors with high on-off switching ratios. More importantly, heterostructures made by stacking different 2D crystals on top of each other provide a platform for creating new artificial crystals with potential for discoveries and applications.
The possibility of making van der Waals heterostructures has been demonstrated experimentally only for a few 2D crystals. However, some of the currently available 2D layers are unstable under ambient conditions, and those that are stable offer only limited functionalities, i.e. low carrier mobility, weak optical emission/absorption, band gaps that cannot be tuned, etc. In a recent series of pilot experiments, we have demonstrated that nanoflakes of the III-VI layer compound, InSe, with thickness between 5 and 20 nanometers, have a "thickness-tuneable" direct energy gap and a sufficiently high chemical stability to allow us to combine them with graphene and related layer compounds to make heterostructures with novel electrical and optical properties. The main goal of this project is to develop graphene-hybrid heterostructures based on this novel class of two-dimensional (2D) III-VI van der Waals crystals. This group of semiconductors will enrich the current "library" of 2D crystals by overcoming limitations of currently available 2D layers and by offering a versatile range of electronic and optical properties. From the growth and fabrication of new systems to the demonstration of prototype devices, including vertical tunnel transistors and optical-enhanced-microcavity LEDs, our project will provide a platform for scientific investigations and will contribute to the technology push required to create new routes to device miniaturization, fast-electronics, sensing and photonics. There is great potential for further growth of all these sectors as the fabrication of 2D systems improves and as new properties are discovered and implemented in functional devices.

From the fabrication and growth of new heterostructures to the demonstration of prototype devices, including transistors, and optical-microcavity-enhanced LEDs and photodetectors, our project will provide a platform for scientific investigations and will contribute to the technology required to create new routes to device miniaturization, fast-electronics, sensing, miniaturised LEDs/photodetectors, and graphene-based integrated optoelectronic circuits.
To maximize this impact, we will promote the adoption of our methods of fabrication, new 2D layers and graphene-hybrid systems to collaborators within the EU GRAPHENE Flagship and interested parties in academia and industry. This will be facilitated by our links to leading international research groups, facilities and industry. In particular, in 2011 Nottingham established a partnership with e2v Technologies ltd, a UK company with over 1500 employees and turnover exceeding £200M (http://www.e2v.com). e2v Technologies ltd. has established a centre within the School of Physics and Astronomy at Nottingham, which manufactures semiconductor devices. e2v Technologies ltd. will work with our team to assess the technical and economic feasibility of a commercial product and provide expertise in identifying routes to technology transfer. The vertical tunnel transistor based on 2D III-VI layers provides an innovative device architecture that will enable access to fast electron speeds at room temperature ; photonic applications of the 2D III-VI layers are also particularly attractive due to the potential to access a wide spectral range across the visible and near-infrared range, and will be explored in collaboration with Helia Photonics ltd, a company specializing in optical coatings for micro-optics and light emitting semiconductor devices. We have also links with the UK National Graphene Institute funded by the EPSRC and Bluestone Global Tech, which has established their European production plant in Manchester. Relationships with industry are central to the operation of the Institute and some of the world's biggest and most influential companies are already working with it on applications of graphene.
The proposed activities align with plans to establish at Nottingham the first Molecular Beam Epitaxy dual-chamber system in the UK for the synthesis of graphene/boron nitride heterostructures (operational in summer 2014). This is part of over £50M UK investment to establish the UK as a graphene research and technology 'hub'. Our work on new 2D van der Waals crystals will both benefit from this new national initiative and will contribute to its expansion by enabling the fabrication of new graphene-hybrid structures.
In addition to the impact arising from research outputs, we highlight the output of 2 post-doctoral researchers and 3 PhD students who will contribute to a new generation of talent and leaders in key scientific areas and whose training will be enhanced through their participation in this project.
In summary, our project will generate transformational impact on science and technology; maintain and enhance the UK leadership in key scientific areas and training; leverage impact through the alignment and collaboration with national and international programmes.