Abstract In this work, H2, CH4, and O2 are used as gas sources and C3H903B is used as the doping source, microwave plasma chemical vapor deposition and a two-steps deposition process will be applied to the growth of boron-doped diamond on p-type(111) silicon substrate. In this work, nucleation and growth of diamond film have been studied. A series of experiments are focused on the depenence of experimental pressure, temperature, power, dc bias, flow rates of O2, and doping concentration of C3H903B. The samples are examined by SEM, Raman, XRD, FTIR, and I-V. The results show that if nucleation is assisted by a negative dc bias, it can reach high density. The growth of diamond and the boron-doped diamond film is in multi steps. After 90 minutes of growth, the mechanism of deposition will be changed.

Chemical Vapor Deposition (CVD) Diamond is a promising technology for the passive cooling of high power Gallium Nitride (GaN) semiconductor devices. The high thermal conductivity diamond can be placed near the junction of the GaN transistor either by direct growth on the backside of the GaN or by bonding it to the GaN. In both cases, the thermal resistance near the interface with the diamond and any semiconductor it is attached to has the potential for large thermal resistance that limits the effectiveness of the diamond layer. In this work, several techniques are developed to understand the thermal conductivity of thin diamond films and the thermal boundary resistance with Si and GaN substrates. Anisotropic thermal conductivity measurements are made using Raman spectroscopy temperature mapping along with electric resistance heating. For devices, the thermal boundary resistance is measured using transistors as the heat source and thermal mapping using Raman spectroscopy. Quick screening methods based on Raman, Fourier Transform Infrared Spectroscopy (FTIR) and X-Ray Photoelectron Spectroscopy (XPS) are also correlated with the thermal properties of the films. Based on this work, the properties of CVD diamond films near the interface of semiconductor substrates is revealed for layers less than 5 µm in thickness and their impact or limitations on thermal management shown through simulations.

Orientador: Teófilo Miguel de Souza / Banca: Celso Eduardo Tuna / Banca: Osiris Canciglieri Junior / Resumo: Visando o conforto e a economia, a ciência, hoje, desenvolve tecnologias capazes de preservar o meio ambiente, diminuindo a perda de energia no processo e na utilização dessas novas técnicas, de forma a garantir um manuseio ecologicamente correto, sem deixar de atender as necessidades do homem. Uma técnica alternativa é o aproveitamento da energia proveniente do sol, que ainda é pouco explorada, podendo ser mais utilizada em coletores solares através do uso de novos materiais. Para isso, o objetivo deste trabalho é comparar o rendimento térmico e o coeficiente global de transferência de calor de materiais como cobre, alumínio e do filme de diamante CVD sobre o silício, pois essas grandezas são essenciais para a caracterização de um bom trocador de calor. Mediante pesquisa experimental foi possível observar que o filme de diamante CVD sobre o silício, mesmo com uma camada muito fina de deposição de filme, mostrou-se mais eficiente no processo de transmissão de calor quando comparado com o cobre e o alumínio / Abstract: To ensure the comfort and economy, science now develops technologies to preserve the environment by reducing energy loss process and the use of these new techniques, to ensure an environmentally friendly handling, while meeting the needs of man. An alternative technique is the use of energy from the sun, which is not explored and may be used in most solar collectors through the use of new materials. For this, the objective is to compare the thermal efficiency and overall coefficient of heat transfer materials such as copper, aluminum and CVD diamond film on silicon, since these quantities are essential for the proper characterization of a heat exchanger. Through experimental research we observed that the CVD diamond film on silicon, even with a very thin film deposition, was more efficient for heat transfer when compared with copper and aluminum / Mestre

Made available in DSpace on 2014-06-11T19:30:10Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-08-01Bitstream added on 2014-06-13T19:39:26Z : No. of bitstreams: 1 dornelas_ln_me_guara.pdf: 431530 bytes, checksum: 5d8aa30beba39823f5403bbf59a82048 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Visando o conforto e a economia, a ciência, hoje, desenvolve tecnologias capazes de preservar o meio ambiente, diminuindo a perda de energia no processo e na utilização dessas novas técnicas, de forma a garantir um manuseio ecologicamente correto, sem deixar de atender as necessidades do homem. Uma técnica alternativa é o aproveitamento da energia proveniente do sol, que ainda é pouco explorada, podendo ser mais utilizada em coletores solares através do uso de novos materiais. Para isso, o objetivo deste trabalho é comparar o rendimento térmico e o coeficiente global de transferência de calor de materiais como cobre, alumínio e do filme de diamante CVD sobre o silício, pois essas grandezas são essenciais para a caracterização de um bom trocador de calor. Mediante pesquisa experimental foi possível observar que o filme de diamante CVD sobre o silício, mesmo com uma camada muito fina de deposição de filme, mostrou-se mais eficiente no processo de transmissão de calor quando comparado com o cobre e o alumínio / To ensure the comfort and economy, science now develops technologies to preserve the environment by reducing energy loss process and the use of these new techniques, to ensure an environmentally friendly handling, while meeting the needs of man. An alternative technique is the use of energy from the sun, which is not explored and may be used in most solar collectors through the use of new materials. For this, the objective is to compare the thermal efficiency and overall coefficient of heat transfer materials such as copper, aluminum and CVD diamond film on silicon, since these quantities are essential for the proper characterization of a heat exchanger. Through experimental research we observed that the CVD diamond film on silicon, even with a very thin film deposition, was more efficient for heat transfer when compared with copper and aluminum

Chemical Vapour Deposition (CVD) diamond detectors were modelled for dosimetry of radiotherapy beams. This was achieved by employing the EGSnrc Monte Carlo (MC) method to investigate certain properties of the detector, such as size, shape and electrode materials. Simulations were carried out for a broad 6 MV photon beam, and water phantoms with both uniform and non-uniform voxel dimensions. A number of critical MC parameters were investigated for the development of a model that can simulate very small voxels. For a given number of histories (100 million), combinations of the following parameters were analyzed: cross section data, boundary crossing algorithm and the HOWFARLESS option, with the rest of the transport parameters being kept at default values. The MC model obtained with the optimized parameters was successfully validated against published data for a 1.25 MeV photon beam and CVD diamond detector with silver/carbon/silver structure with thicknesses of 0.07/0.2/0.07 cm for the electrode/detector/electrode, respectively. The interface phenomena were investigated for a 6 MV beam by simulating different electrode materials: aluminium, silver, copper and gold for perpendicular and parallel detector orientation with regards to the beam. The smallest interface phenomena were observed for parallel detector orientation with electrodes made of the lowest atomic number material, which was aluminium. The simulated percentage depth dose and beam profiles were compared with experimental data. The best agreement between simulation and measurement was achieved for the detector in parallel orientation and aluminium electrodes, with differences of approximately 1%. In summary, investigations related to the CVD diamond detector modelling revealed that the EGSnrc MC code is suitable for simulation of small size detectors. The simulation results are in good agreement with experimental data and the model can now be used to assist with the design and construction of prototype diamond detectors for clinical dosimetry. Future work will include investigating the detector response for different energies, small field sizes, different orientations other than perpendicular and parallel to the beam, and the influence of each electrode on the absorbed dose.

Chemical Vapour Deposition (CVD) diamond detectors were modelled for dosimetry of radiotherapy beams. This was achieved by employing the EGSnrc Monte Carlo (MC) method to investigate certain properties of the detector, such as size, shape and electrode materials. Simulations were carried out for a broad 6 MV photon beam, and water phantoms with both uniform and non-uniform voxel dimensions. A number of critical MC parameters were investigated for the development of a model that can simulate very small voxels. For a given number of histories (100 million), combinations of the following parameters were analyzed: cross section data, boundary crossing algorithm and the HOWFARLESS option, with the rest of the transport parameters being kept at default values. The MC model obtained with the optimized parameters was successfully validated against published data for a 1.25 MeV photon beam and CVD diamond detector with silver/carbon/silver structure with thicknesses of 0.07/0.2/0.07 cm for the electrode/detector/electrode, respectively. The interface phenomena were investigated for a 6 MV beam by simulating different electrode materials: aluminium, silver, copper and gold for perpendicular and parallel detector orientation with regards to the beam. The smallest interface phenomena were observed for parallel detector orientation with electrodes made of the lowest atomic number material, which was aluminium. The simulated percentage depth dose and beam profiles were compared with experimental data. The best agreement between simulation and measurement was achieved for the detector in parallel orientation and aluminium electrodes, with differences of approximately 1%. In summary, investigations related to the CVD diamond detector modelling revealed that the EGSnrc MC code is suitable for simulation of small size detectors. The simulation results are in good agreement with experimental data and the model can now be used to assist with the design and construction of prototype diamond detectors for clinical dosimetry. Future work will include investigating the detector response for different energies, small field sizes, different orientations other than perpendicular and parallel to the beam, and the influence of each electrode on the absorbed dose.

No description available.

GaN is a monocrystalline material that can be grown using metallo-organic chemical vapour deposition (MOCVD), and has desirable mechanical and semiconducting properties for operating as a sensor. It has a Young’s modulus of 250 to 350 GPa, which shows little decrease with respect to temperature beyond 400°C. GaN also exhibits piezoelectric and piezoresistive effects, meaning that it will generate a charge and its electrical resistance will change when the material is strained respectively. In this PhD, GaN has been used as the base material for pressure sensors that potentially can be used in excess of 400°C and at a pressure in excess of 50 bar (5 MPa), with potential applications in aerospace and oil exploration. The pressure sensor is a circular diaphragm created from a GaN/sapphire wafer, and was designed and tested in order to determine if GaN can act as a sensing material in these environments. In addition to the diaphragm sensor, GaN templates that can potentially be used for sensors were grown using an epitaxial layer overgrowth (ELOG) method. These sensors are potentially more mechanically robust than similar templates etched out of GaN/sapphire wafers because they will have less inbuilt strain due to lower dislocation densities. It was possible to release beams and cantilevers from GaN ELOG templates. Mechanical probe tests were undertaken on these devices to see if they were fully released and robust. GaN single crystal growth requires a substrate material, such as (111) silicon or (0001) sapphire, meaning that the thermal properties of the substrate are important for a device operating in excess of 400°C. GaN high electron mobility transistors are heat sensitive, experiencing a decrease in current between the drain and source terminals as the temperature increases. Therefore a GaN-based sensor needs a substrate with the highest possible thermal conductivity to act as a heat sink, which means removing as much heat as possible from the GaN sensor. Diamond has superior thermal conductivity to both sapphire and silicon, so a novel silicon/polycrystalline diamond composite substrate has been developed as a potential GaN substrate. Polycrystalline diamond (PD) can be grown on 4 inch diameter wafers using hot filament chemical vapour deposition (CVD), on (111) silicon (Si) from which single crystal GaN epitaxy can also be grown. In order for the (111) Si/PD composite substrates to be useful heat sinks, the Si layer needs to be less than 2 m. PD was initially grown on 525 to 625 m thick Si wafers that required thinning to 2 m. Achieving this Si layer thickness is difficult due to the presence of tensile stress in the Si caused by a mismatch in the coefficients of thermal expansion (CTEs) between Si and PD. This stress causes the wafer to bow significantly and has been modelled using ANSYS FE software. The models show that the bow of the wafer increases when it is thinned, which will eventually cause the Si layer to delaminate at the Si/PD interface due to poor adhesion and a build up for shear stress. When the Si layer is mechanically thinned, the Si layer can crack due to clamping. The experimental wafer bow and micro-Raman measurements validate the model for when the silicon layer is thicker than 100 m and these results show that an alternative processing route is required.

In the study, the effect of current density and rotation speed of grinding disk on characters of Ni-Diamond composite coating are investigated. Experimental results show that current density and film thickness are almost linearly depend. When the current density is increased, the film thickness is increased, too. And it can cover diamond particles much more efficiently. The rotation speed of grinding disk is 20 rpm, the average deposition rate is approx. 2£gm/min in 5 ASD. When reduce the current density to 2.5ASD, the average deposition rate reduce to approx. 1.08£gm/min. The current density is 5 ASD, the covered area of diamond particle in Ni-Diamond composite coating is 60% when the rotation speed of grinding disk is 0rpm. Increasing the rotation speed up to 100 rpm, the covered area of diamond particle in Ni-Diamond composite coating is down to 24% because diamond particle can`t stay in the same position in a long period. Secondary, we use composite electroplating on grinder in process to grind CVD diamond films, the effect of current density and loads on grinding characters of CVD diamond films by using the composite electroplating on grinder in process are investigated. The load is 4.2 kg, the surface roughness Ra is about 0.2 £gm when composite coating grind CVD diamond with no electroplating. But the current density is up to 2.5 ASD, Ra can down to 0.12£gm. The load is increasing to 6.3 kg, the Ra of CVD diamond films is about 0.16£gm.

This work has employed the Micro-wave Plasma enhanced Chemical Vapor Deposition (MPCVD) method to fabricate diamond PN junction device. The n+ <111> orientation single-crystal silicon has used as substrates. P-type diamond layer is doped with B(OCH3)3 and the N-type diamond layer is doped with ammonia. The surface structure of diamond film has been observed by scanning electron microscope; and the device rectification property of a PN junction has measured by current-voltage characteristic. The carrier density and mobility of diamond films have been analyzed by Hall measurement. Furthermore, the Cathodoluminescence (CL) spectroscopy showed the defect spectra in diamond PN junction. The N-type diamond film and P-type diamond film have deposited at temperature of 800 ¢J, for 30 minutes and 90 minutes, respectively. The process CVD has performed in the same chamber continually. A I-V curve of sample showed the set on positive voltage 0.5 V and the reverse breakdown voltage of 6 V. Further, CL results revealed a peak at 285 nm (4.4 eV), which represents the CVD diamond band and the other one is at 500 nm (2.5 eV), which stands for donor-acceptor recombination from defect in these diamond films.