Silicon Valleytronics

Lead Research Organisation: University of Bath
Department Name: Physics


Harnessing the interface between silicon and its thermal oxide has had, and continues to have, enormous impact on humankind through the crucial role it plays in metal-oxide-semiconductor transistors. These transistors can be found in anything containing integrated circuitry like computers. Due to the importance of this interface, vast efforts were made to understand the underlying physics around three decades ago and as such, it is often assumed that most of the pertinent physics is well understood.However, along with extreme miniaturisation and the developing interest in quantum information processing, we are now entering into an exciting new era where our understanding of silicon is tested in ways only dreamt about thirty years ago. Miniaturisation has come so far, that cross-sectional micrographs of cutting-edge transistors can now show individual atomic structures on the same picture encompassing an entire device. In such small devices, and indeed in emergent devices aimed at manipulating quantum information, details such as atomic layer fluctuations of an interface and quantum mechanical effects come to the fore. These have enormous effects on device properties, rendering further progress critically dependent on our ability to understand and control them. This is leading to a world-wide revival of interest in the basic physics of silicon. As an unexpected and surprising result of this endeavour, recent experiments have revealed, that when the interface is prepared in a particular manner, the band-structure of silicon is profoundly altered in a completely new way which we call giant valley-splitting . The band-structure of a material lies at the very heart of the physics of any crystalline solid - it dictates all properties involving electrons such as how suitable the material is for use in a transistor, and what colour of light the material absorbs and emits.Despite silicon-silicon dioxide being one of the most important interfaces in the infrastructure of modern society, at present, we know very little about this effect. We do not have a quantitative theory to explain it; we do not know what microscopic structural parameters determine it; we do not know what exact preparation parameters determine it, and we do not know how it affects other physical properties except limited aspects of electrical conductivity. In this respect, this silicon-silicon dioxide interface is a new material with yet-unknown properties.The aim of this project is to understand the origin and consequences of this new interface so that we can harness it as a new ingredient for physics of low dimensional systems and technology of semiconductor devices. Since the material is made from silicon and silicon dioxide, it is automatically compatible with the vast arsenal of cutting-edge silicon technology. New properties and resulting functionalities can be embedded into existing silicon based systems at the deepest level of integration which is impossible with any other material.

Planned Impact

Who will benefit from this research? Outside academic and basic research communities, the main benefits of this research will be to the microelectronics and telecommunications industry with their vast range of stakeholders worldwide. How will they benefit from this research? Since our new material is compatible with silicon technology at the most fundamental level, discovering new properties and gaining new insights will benefit the development of truly ubiquitous devices such as transistors found in their billions in every computer. Control over the valley degree of freedom will equip device engineers with a new handle with which to tackle the challenges of extending Moore's Law. New physical properties will also enable new functionalities. Due to the unique scalability and integrability of silicon, creating new functionalities for silicon has unparalleled potential for impact. What will be done to ensure that they have the opportunity to benefit from this research? We will present relevant results of our research in fora attended by communities engaged in industrial research and development such as the annual Silicon Nanoelectronics Workshop which is held alongside the VLSI (Very Large Scale Integration) symposia on technology and circuits. We will also seek to write patents where appropriate. Resulting technology will be commercialised where possible, working closely with Bath Ventures at the University of Bath. We will also exploit the capabilities and networks of our partner organisation in the telecommunications industry (Nippon Telegraph and Telephone Corporation (Japan)) to maximise the economic impact of our work. A collaboration agreement is already in place and extends beyond the proposed period of the project. Since the research is based on collaboration with a large-scale high-profile international partner, the success of this project will also serve to demonstrate that the UK is indeed the best place in the world to engage in research and innovation. It will encourage further collaborations of this kind and scientifically motivated inward investment.


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Description We have been able to obtain new insights into how valley splitting and valley polarization affect electronic properties of silicon based two-dimensional electronic systems, and how they relate to spin polarization. We have also obtained further insights that have allowed us to enhance our ability to engineer valley splitting in these systems.
Exploitation Route Our findings relate to quantum transport phenomena and the control of electronic states. We expect that our findings would be useful in engineering silicon based quantum electronic devices in the future.
Sectors Digital/Communication/Information Technologies (including Software),Electronics

Description Scientific data obtained from this research continue to be used to provide new insights into the impact of valley degeneracy and valley polarization on the electronic properties of two-dimensional electronic systems.