Room-Temperature Single Atom Silicon Quantum Electronics

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In recent years, it has become possible to define semiconductor quantum electronic switches in silicon using individual impurity atoms within a semiconductor crystal. This reduces the switching 'core' of an electronic device to the ultimate, atomic scale limit. Furthermore, electronic charge in the discrete, quantum states of the impurity atom may be controlled at the level of individual electrons, also reducing the size of information 'bits' from many thousands to a few, or even single electrons. 'Single-atom quantum dot transistors' (SA-QDTs) such as these hold great promise for a wide range of applications, including ultra-low power highly scaled nanoelectronics, single charge/molecule sensors, metrological standards and quantum computation. Achieving wide-scale, general application of SA-QDTs, e.g. in nanoelectronics or ultra-high sensitivity sensing, requires both room-temperature (RT) operation and large-scale manufacturability. However, at present the potential of these devices has remained unfulfilled, due to problems such as electrical operation at only cryogenic temperatures, the use of materials lacking large scale device manufacturability, or a lack of compatibility with current silicon electronic circuits technology, etc. Recently, we have demonstrated RT operation in silicon SA-QDTs based on phosphorus (P) dopant atoms embedded in ~10 nm scale Si-SiO2-Si point-contacts, fabricated by electron beam lithography. Both single and double, coupled, QD RT operation have now been demonstrated. The fabrication of these devices in silicon is completely compatible with conventional large-scale, Si electronic circuit nanofabrication technology. In complementary work to the above, we have also demonstrated methods to locate impurity atoms at precise atomic scales using advanced scanning probe lithographic (SPL) techniques.The central aim of this project is to develop useful RT SA-QDT devices, circuits and sensors in silicon. In doing this we propose to move from the present level of individual devices to 'proof-of-principle' RT circuits with ~10 devices. We will also develop single-molecule sensors based on SA-QDTs, exploiting the sensitivity of these devices to changes in surface charge at the level of <1e. We propose to build memory cell, logic gate and single-molecule sensor circuits, using both electron-beam and scanning probe lithographic methods. We will also extend our fabrication methods for atomically precise nanofabrication using hydrogen depassivation SPL, to establish structural precision at this scale for the first time in devices operating at RT. Simulation methods, from the individual device to circuit level, will be developed to establish design rules for single-atom electronic systems. Successful completion of this project will realise the potential of single-atom devices for quantum nanoelectronic circuits and single-molecule sensors, opening the way for a future large-scale atomic electronics technology.