Diamond Structures for Advanced Electronics

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

Simultaneous conduction and valence band quantisation in ultra-shallow, high density doping profiles in semiconductors

We demonstrate simultaneous quantisation of conduction band (CB) and valence band (VB) states in silicon using ultra-shallow, high density, phosphorus doping profiles (so-called Si:P $\delta$-layers). We show that, in addition to the well known quantisation of CB states within the dopant plane, the confinement of VB-derived states between the sub-surface P dopant layer and the Si surface gives rise to a simultaneous quantisation of VB states in this narrow region. We also show that the VB quantisation can be explained using a simple particle-in-a-box model, and that the number and energy separation of the quantised VB states depend on the depth of the P dopant layer beneath the Si surface. Since the quantised CB states do not show a strong dependence on the dopant depth (but rather on the dopant density), it is straightforward to exhibit control over the properties of the quantised CB and VB states independently of each other by choosing the dopant density and depth accordingly, thus offering new possibilities for engineering quantum matter.Comment: 5 pages, 2 figures and supplementary materia

Probing Electron-Phonon Interactions Away from the Fermi Level with Resonant Inelastic X-Ray Scattering

Interactions between electrons and lattice vibrations are responsible for a wide range of material properties and applications. Recently, there has been considerable interest in the development of resonant inelastic x-ray scattering (RIXS) as a tool for measuring electron-phonon (e-ph) interactions. Here, we demonstrate the ability of RIXS to probe the interaction between phonons and specific electronic states both near to, and away from, the Fermi level. We perform carbon K-edge RIXS measurements on graphite, tuning the incident x-ray energy to separately probe the interactions of the π∗ and σ∗ electronic states. Our high-resolution data reveal detailed structure in the multiphonon RIXS features that directly encodes the momentum dependence of the e-ph interaction strength. We develop a Green’s-function method to model this structure, which naturally accounts for the phonon and interaction-strength dispersions, as well as the mixing of phonon momenta in the intermediate state. This model shows that the differences between the spectra can be fully explained by contrasting trends of the e-ph interaction through the Brillouin zone, being concentrated at the Γ and K points for the π∗ states while being significant at all momenta for the σ∗ states. Our results advance the interpretation of phonon excitations in RIXS and extend its applicability as a probe of e-ph interactions to a new range of out-of-equilibrium situations

Simultaneous Conduction and Valence Band Quantization in Ultrashallow High-Density Doping Profiles in Semiconductors

We demonstrate simultaneous quantization of conduction band (CB) and valence band (VB) states in silicon using ultrashallow, high-density, phosphorus doping profiles (so-called Si:P δ layers). We show that, in addition to the well-known quantization of CB states within the dopant plane, the confinement of VB-derived states between the subsurface P dopant layer and the Si surface gives rise to a simultaneous quantization of VB states in this narrow region. We also show that the VB quantization can be explained using a simple particle-in-a-box model, and that the number and energy separation of the quantized VB states depend on the depth of the P dopant layer beneath the Si surface. Since the quantized CB states do not show a strong dependence on the dopant depth (but rather on the dopant density), it is straightforward to exhibit control over the properties of the quantized CB and VB states independently of each other by choosing the dopant density and depth accordingly, thus offering new possibilities for engineering quantum matter

The occupied electronic structure of ultrathin boron doped diamond

Funding: RBJ acknowledges the UK's Engineering and Physical Sciences Research Council (EPSRC) for partial funding for this activity (EP/H020055/1) as well as The EC's Horizon 2020 Programme for support from the “GREENDIAMOND” project (ID: 640947). This work was supported by the Research Council of Norway through its Centres of Excellence funding scheme, Project No. 262633, “QuSpin”, and through the Fripro program, Project No. 250985 “FunTopoMat” and 262339 “NEAT”. This work was supported by the Danish Council for Independent Research, Natural Sciences under the Sapere Aude program (Grants No. DFF-4002-00029 and DFF-6108-00409) and by VILLUM FONDEN via the Centre of Excellence for Dirac Materials (Grant No. 11744) and the Aarhus University Research Foundation.Using angle-resolved photoelectron spectroscopy, we compare the electronic band structure of an ultrathin (1.8 nm) δ-layer of boron-doped diamond with a bulk-like boron doped diamond film (3 μm). Surprisingly, the measurements indicate that except for a small change in the effective mass, there is no significant difference between the electronic structure of these samples, irrespective of their physical dimensionality, except for a small modification of the effective mass. While this suggests that, at the current time, it is not possible to fabricate boron-doped diamond structures with quantum properties, it also means that nanoscale boron doped diamond structures can be fabricated which retain the classical electronic properties of bulk-doped diamond, without a need to consider the influence of quantum confinement.Publisher PDFPeer reviewe

Radiation tolerance of diamond detectors

International audienceDiamond is used as detector material in high energy physics experiments due to its inherent radiation tolerance. The RD42 collaboration has measured the radiation tolerance of chemical vapour deposition (CVD) diamond against proton, pion, and neutron irradiation. Results of this study are summarized in this article. The radiation tolerance of diamond detectors can be further enhanced by using a 3D electrode geometry. We present preliminary results of a poly-crystalline CVD (pCVD) diamond detector with a 3D electrode geometry after irradiation and compare to planar devices of roughly the same thickness