Andre Frota
Heteroepitaxial boron-doped diamond: from synthesis to application
Supervisor: Prof. Dr. Bernd Stritzker [Experimental physics IV]
Date of oral examination: 05/31/2016
220 pages, english
This thesis focusses on synthesis of boron-doped, heteroepitaxial diamond grown on Ir/YSZ/Si(001). Gas phase processes during Chemical Vapour Deposition (CVD) was investigated by Optical Emission Spectroscopy (OES), in order to monitor and control B-doping of diamond, and to understand mutual interaction with other gas species, such as O and N. In particular, the effect of B on the growth rate enhancement by N was studied, and it was found that growth rate threshold between standard and accelerated growth corresponds to an incorporated N/B ratio close to unity. The influence of B incorporation in diamond films with high dislocation densities was investigated. It was demonstrated that, for the correct estimation of B incorporation by CL and XRD, a biaxial stress component must be separated from the hydrostatic stress component caused by the B incorporation-induced lattice expansion. The identification of dislocations by selective etching was studied. Etch-pit formation was found to depend substantially on process parameters. The shape of the etch-pits was explained in terms of crystallographic planes and off-axis direction. It was demonstrated that the inner facets of the etch-pits switch from lower to higher index planes with increasing temperature or with decreasing pressure. Combined TEM and EELS analysis have shown that dislocations in heavily B-doped diamond tilt towards [001] and are enriched with B. Furthermore, B in the dislocations are embedded tetrahedrally and also in lower coordination. Heteroepitaxial B-doped diamond films were investigated for the first time as electrodes for electrochemical applications. It was demonstrated that they present much improved merits compared with polycrystalline diamond, showing wide potential window of 3.3 V, lower background current, resistance to fouling by polar adsorbates and much higher electrochemical homogeneity across the surface. The results are comparable with high-quality B-doped diamond single crystal electrodes. Heteroepitaxial diamond was for the first time applied as Schottky barrier diodes for high-power applications, showing very high rectification ratio of 10 orders of magnitude and very low on-state resistance for Ni-diamond junctions. The measured performance in forward bias approached that of state-of-the-art devices built with high-quality homoepitaxial crystals. Reverse blocking voltages of 600-700 V was demonstrated with heteroepitaxial diamond for the first time using Ir as a Schottky contact. The work presented in this thesis contributes with a humble step towards one of mankind%92s biggest goals: the need to produce clean and renewable energy and to use it in an efficient manner.