Afandi, Abdulkareem; (2018) Electronic properties of doped-nanoscale diamonds. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Nanodiamonds (ND) have been the subject of intense research in recent years, for they have unique physical properties normally associated with diamond, in addition to their rich surface chemistry and bio-compatibility. In this thesis, the electronic properties of intentionally boron-doped nanodiamond materials are studied. In chapter 5, the possibility of substitutional doping of NDs is investigated. The properties of boron-doped, detonation nanodiamonds (B-DND) are studied using electrical impedance measurements and spectral analysis, and are compared to un-doped detonation-NDs (DND). Activation energies from variable-temperature impedance spectroscopy are found to be lower in comparison to intrinsic NDs. Chapter 6 discusses the nucleation of high-pressure, high-temperature (HPHT) boron-NDs, as well as B-DNDs on silicon. By combining pH titration and ultra-sonication from solution, nucleation densities are measured using atomic force microscopy (AFM). It is found that for most samples, highly acidic solutions (pH~2) are ideal for high surface coverage. Chapter 7 describes the electrical properties and activation energies of boron-doped HPHT and detonation nanodiamonds. Thin films are aggregated on conductive silicon substrates, and are subjected to electrical impedance measurements in vacuum. Following vacuum annealing, electrical measurements showed activation energies comparable to highly boron-doped PE-CVD thin film diamond. Electrical conductivity and resistivity are also compared to literature. In chapter 8, aluminium-diamond Schottky-barrier diodes (SBD) are fabricated. HPHT nanodiamond films were used as both Ohmic contacts and as a source of dopant (boron), where aggregated nanodiamonds were subjected to PE-CVD film growth. Electrical (I-V) and capacitance-voltage (C- V) measurements are performed to study conduction mechanisms in fabricated devices. Resulting devices are found to have low carrier densities in the grown active layer (~1015 cm-3), which is desirable for SBDs. This is the first account of using doped-NDs as the source of low boron-doping in PE- CVD diamond films, paving the way for potentially economical nanoscale diamond electronic devices.

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