Chemical Vapor Deposition最新文献

A 3-dimensional (3D) computational fluid dynamics (CFD) simulation study on the effect of temperature and carrier-gas flow rate on the deposition of photocatalytic titanium dioxide (TiO₂) nanoparticles by metal-organic (MO)CVD is presented. The model predicts the temperature, velocity, mass fraction of reactants and products, kinetic rate of reaction, and surface deposition rate profiles. Increasing temperature and reducing carrier gas flow rate increases the deposition rate and hence the amount of nanoparticles produced. Unlike carrier-gas flow rate, temperature is significant in determining the rate of surface deposition. Simulation results are validated by experiments whenever possible due to limited data. Decent agreement between experiment and simulation supports the reliability of the simulation.

To deposit a film with uniform thickness, flow rectifiers are often used in a CVD reactor. Despite the effectiveness of these rectifiers, some degree of flow non-uniformity persists within the reaction chamber, due to variations in the flow and buoyancy effects. Here, the non-uniformity caused by the non-axisymmetric pumping system, specifically a single and non-annular pumping outlet, is investigated. A pumping liner, which directs the fluid mixture through embedded channels into a ring chamber connected to the pumping outlet, is used to improve flow uniformity. The flow resistance associated with each component in the pumping system is analyzed, then two carefully designed pumping liners, the channels of which either have non-uniform radii or are unevenly spaced, are proposed. The pumping effect is balanced through the non-uniform channel flow resistances, giving an axisymmetric flow field in the reaction chamber. This balance is confirmed in simulations.

A mixture of carbon micro- and nanocoils (CMCs/CNCs) is synthesized by catalytic pyrolysis of acetylene at 650 °C using NiSO₄ as the catalyst precursor. The morphology of the grown product is analyzed by scanning electron microscopy (SEM). Experimental results indicate that, in general, the CMCs are in double-helical form, while most of the grown CNCs are in twisted single-helical form. The coil diameters of CMCs and CNCs are approximately 4 to 10 mm and 300 to 400 nm, respectively. Raman spectra indicate that the real active catalyst precursor for growing CMCs/CNCs is NiSO₄, while NiO is not an effective catalyst precursor for synthesizing CMCs or CNCs.

Iridium thin films are deposited on sub-micrometer three-dimensional trench structures by plasma-enhanced metal-organic chemical vapor deposition (PE-MOCVD). The iridium precursor used in this study is (ethylcyclopentadienyl)(1,5-cyclooctadiene)iridium [Ir (EtCp)(1,5-COD)]. Various process conditions at substrate temperatures from 300 °C to 450 °C, with and without plasma enhancement, are investigated and compared. Crystal structure of the deposited iridium films is analyzed by X-ray diffraction (XRD). Step coverage of the deposited iridium films on three-dimensional trench structures is analyzed by scanning electron microscopy (SEM). Surface morphology is quantitatively evaluated by atomic force microscopy (AFM) and the electrical resistivity of the deposited Ir films is measured by the four-point probe method.

Atmospheric pressure (AP) thermal CVD is used to deposit thin poly-Si films on glass substrates. Also produced are heterojunction solar cells carrying out the deposition on c-Si wafers. A batch-type hot-wall reactor, employing SiHCl₃ as a precursor, H₂ as a carrier and reaction gas, BBr₃ as a p-type doping agent, and PCl₃ as a n-type doping agent, is used. The films obtained are homogeneous and well-adhered to the substrate. Samples are structurally characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), reflectance spectroscopy in the UV-vis region, X-ray diffraction (XRD), and Raman spectroscopy (RS). The electrical characterization includes conductivity measurements as a function of temperature, and Hall effect measurements. For the p-doped samples, XRD reveals a strong (220) preferential orientation of the films, while the n-doped samples lack columnar structure or preferential orientation. RS and UV-reflectance confirm a high crystalline fraction. Dark conductivity measurements as a function of temperature show that the films can be grown intrinsic, p-type or n-type. Activation energies between 0.61 and ∼0 eV are obtained, with reasonable values for the carrier mobilities. For the solar cells, relatively high values of V_OC(∼507 mV) and J_SC (∼29.6 mA cm⁻²) are measured. In conclusion, these results demonstrate the feasibility of directly depositing doped poly-Si thin films on glass and c-Si substrates at intermediate temperatures, with interesting characteristics for photovoltaic applications.

The improvements in electrical characteristics of AlGaN/GaN high electron mobility transistors (HEMTs) grown using metal-organic (MO)CVD by engineering structure, barrier strain, and unintentional carbon incorporation, are demonstrated in this work. Both normal HEMT structure (with a high temperature (HT) AlN buffer) and advanced HEMT structure (with a high-low-high temperature (HLHT) AlN buffer, and a HT AlN interlayer (IL)) present a breakdown voltage higher than 200 V, while a much smaller breakdown voltage of 17 V is measured on the conventional structure using a low-temperature GaN buffer. The HT AlN IL inserted in the middle of the conventional HEMT structure introduces a reduction in the tension of the AlGaN barrier, which results in an improvement of the surface morphology (0.46 nm). As a consequence, the two-dimensional electron gas (2DEG) mobility increases by remarkable 46% (1900 cm² V⁻¹ s⁻¹). The HLHT AlN buffer, substituting for the HT AlN buffer, leads to the enhancement of GaN crystalline quality, which contributes to the performance improvement for HEMTs. The advanced HEMT, using both an AlN IL and an HLHT AlN buffer, produces increases in the DC maximum drain current by 35.5% (∼680 A mm⁻¹), and in the transconductance by 15% (114 mS mm⁻¹) in comparison with the normal HEMT with an AlN buffer. The very low leakage current in the advanced HEMTs is caused by optimizing the design of the buffer and modifying growth parameters. Lastly, the reduction of AlGaN barrier tensile strain by inserting the HT AlN IL is promising for an improvement in AlGaN/GaN HEMT reliability.