Pakpour-Tabrizi, A. C.; (2017) Diamond Structures for Advanced Electronics. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Although diamond is slowly becoming an advanced technology there is con- tradictory information and misunderstanding surrounding the fundamental electronic attributes of the material system. In particular, the properties of boron doped diamond for electronics on quantum length scales has yet to be fully understood or utilized within devices. In this thesis, new insight into the electronic band structure of boron doped diamond on nano and macro scales is found and novel planar boron doped nanowires are fabricated electronically probed and a new type of side gated diamond nanowire transistor conceived. High quality single crystal diamond with thin δ-shaped boron-doped epi- layers have been thought to offer a viable approach towards transistors that can operate at high speed, high power and high temperatures. δ-doping diamond has been conjectured to achieve high mobilities and carrier con- centrations, properties of real interest for electronic applications. Taking advantage of diamond’s thermal and electronic properties, thin films can be incorporated into realistic nanoscale devices more easily than the parent bulk system. Using angle-resolved-photoemission spectroscopy (ARPES), the electronic structure of bulk and thin films (≈ 2 nm) of boron-doped di- amond are uncovered. Surprisingly, the ARPES measurements do not reveal any significant differences for these systems, irrespective of their physical dimensionality. This suggests that it is possible to grow nearly atomic-scale structures whilst still preserving the properties of bulk diamond, facilitating the use of thin films diamond for devices which necessitate nearly atomic- scale components. Using a range of techniques such as Secondorary Ion Mass, Angle Resolved Photo-emission and Raman Spectroscopy we compare thin boron doped delta layers (BDDδl) and effectively infinite, thick bulk Boron doped di- amond. We see remarkably little electronic difference and hints of low dimensional transport in both films. Using photo-lithography and Reactive Ion Etching processes, macro scale devices are fabricated, these are charac- terized using Hall effect techniques. For the first time, lateral boron doped diamond nanowires are defined using electron beam lithography. These nanowires are then processed into a variety of novel transistor like devices, showing exciting emergent quantum properties as well as classical transistor like behaviour. In developing the techniques and methods to fabricate structures in diamond we find a variety of processes require optimisation and develop a skill base to handle small and sometimes fragile substrates and process them into devices.

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