Logotyp: till Uppsala universitets webbplats

Diamond is a wide band semiconductor with fascinating electrical and physical properties. It has high thermal and electrical conductivity, high electrical breakdown field, high radiation hardness and is chemically inert. These properties make diamond an excellent material for high power electronics, high frequency electronics, particle detectors and for electronics in hazardous environments. Moreover, diamond has been suggested for applications in valleytronics.

Valleytronics is a term for semiconductor technology that exploits minima in an energy band, so called valleys. In diamond there are six of these valleys in the conduction band and the conduction electrons resides in one of these six valleys at low temperatures. The valley an electron is in, its valley polarization, affects how it behaves in an electric field. The valley polarization along with an understanding of the electron-phonon scattering processes makes a good framework for understanding of electron transport in diamond. In this thesis, both of these topics have been explored, with the purpose of understanding low temperature electron transport in diamond. A detailed description of low temperature charge transport is relevant for several reasons. Firstly, it can help with understanding the charge transport in e.g. detectors. Secondly, it gives more degrees of freedom when designing new electronics.   

In this thesis, both experiments and simulations has been used investigate low temperature transport in diamond. The main experiment method used was time-of-flight were the drift current of valley polarized electrons measured between two contacts. These experiment could then be compared with Monte Carlo simulations. The simulations gave valuable insigne into the dynamics of the electrons. This self-written code for Monte Carlo simulations is described in greater detail in this thesis. 

Some highlighted results of this thesis are as follows: optical observations of valley polarized diffusion, electrical control of valley polarized currents and the estimations of the acoustic deformation potentials to D_u = 18.5 eV and D_d = -5.7 eV. This thesis also includes a more general part about charge transport.

Diamond and graphene are two unique carbon allotropes whose exceptional properties, extensively investigated separately, make them attractive for next-generation electronics. Diamond combines ultra-high thermal conductivity, a wide bandgap, excellent mechanical robustness, and chemical inertness, enabling efficient heat dissipation and high breakdown fields. Graphene, by contrast, is a two-dimensional material with extremely high carrier mobility and outstanding electrical conductivity arising from its Dirac-cone band structure. These attributes have sparked strong interest in integrating graphene with diamond to realize high-power, high-frequency, and quantum-compatible devices.

However, reproducible fabrication of graphene-based devices and a comprehensive understanding of the physical and chemical properties of the graphene/diamond interface are still lacking. Furthermore, the physical and chemical properties of the graphene/diamond heterostructure remain incompletely explored.

This thesis investigates two routes for forming graphene/diamond interface —rapid direct growth on (100) single-crystalline diamond (SCD) using a Nickel (Ni) catalyst at high temperature (1073 K), and wet transfer of commercial CVD graphene— and evaluates their electrical and quantum-sensing performance. Direct growth yields predominantly multilayer graphene with only ~20% monolayer coverage due to high carbon solubility in Ni, resulting in a room-temperature Hall mobility of ~79 cm²V⁻¹s⁻¹, underscoring challenges such as Ni dewetting and non-uniform precipitation. In contrast, transferred graphene on electronic-grade SCD with low Nitrogen concentration(< 5 ppb) attains derived hole Hall mobilities up to 2750 cm²V⁻¹s⁻¹ and exhibits weak temperature dependence from 80 K to 300 K, indicating that charged-impurity scattering is strongly suppressed.

Surface-termination engineering, such as plasma O-termination and thermal H-termination, further improves low-temperature mobility, increasing from 1238 to 1640 cm²V⁻¹s⁻¹ and reveals distinct remote-interfacial-phonon energies, ~60 meV and ~114 meV, for O- and H-termination types respectively. Electrical robustness is demonstrated by current densities exceeding 1×10⁹ A/cm², surpassing limits on conventional substrates such as SiO₂.

Photoelectric detection of magnetic resonance (PDMR) of NV ensembles operates reliably from 77 K to 395 K, yielding a zero-field-splitting temperature coefficient dD/dT ~73 kHz/K and magnetic-field sensitivities comparable to conventional ODMR, thereby providing an on-chip electrical readout pathway for quantum sensing.

The goal is to develop a fabrication process and investigate its properties. Ultimately, this study aims to explore the potential of graphene-on-diamond for electronic devices and to identify factors that can optimize their performance.