High-pressure CVD Research Articles

Carbon Nanostructures Produced by High Pressure CVD

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Growth temperature - phase stability relation in In1-xGaxN epilayers grown by high-pressure CVD

AbstractThe influence of the growth temperature on the phase stability and composition of single-phase In1-xGaxN epilayers has been studied. The In1-xGaxN epilayers were grown by high-pressure Chemical Vapor Deposition with nominally composition of x = 0.6 at a reactor pressure of 15 bar at various growth temperatures. The layers were analyzed by x-ray diffraction, optical transmission spectroscopy, atomic force microscopy, and Raman spectroscopy. The results showed that a growth temperature of 925°C led to the best single phase InGaN layers with the smoothest surface and smallest grain areas

Characterization of boron-doped diamonds using 11B high-resolution NMR at high magnetic fields

11B static/magic-angle spinning (MAS) NMR experiments are applied to four different B-doped diamond samples prepared by either high-pressure and high-temperature (HPHT) or CVD methods with various starting materials. Application of MAS enhances the spectral resolution appreciably and differences of the four B-doped diamond samples are well reflected in the corresponding MAS spectra. From the comparison among the MAS spectra, and also their dependences on the magnetic-field and the pulse-flip angle, it is suggested that at least four kinds of boron including two kinds of impurities exist in B-doped diamond. We further examine 11B spin-lattice relaxation times ( T 1) for the four components and find that one of them is extremely short (ca. 500 ms) while others are in the range of several seconds. Relation between the component having the short T 1 and the super conducting transition temperature ( T c) value is suggested.

Properties of InN layers grown by High Pressure CVD

ABSTRACTIndium nitride (InN) and indium-rich group III-nitride alloys are promising materials for advanced optoelectronic device applications. Indium-rich alloys, e.g. (Ga1-y-xAlyInx)N will enable the fabrication of high-efficient light emitting diodes tunable in the whole visible spectral region, as well as advanced high speed optoelectronics for optical communication operating. The present limitation in this area is the growth of high quality InN and indium-rich group III-nitride alloys as documented in many controversial reports on the true physical properties of InN. The difficulties arise from the low dissociation temperature of InN that requires an extraordinarily high nitrogen overpressure to stabilize the material up to optimum growth temperatures. We developed a novel “high-pressure chemical vapor deposition” (HPCVD) system, capable to control and analyze the vast different partial pressures of the constituents. Our results show that the chosen HPCVD pathway leads to high-quality single crystalline InN, demonstrating that HPCVD is a viable tool for the growth of indium rich group III nitride alloys. The structural analysis of InN deposited on GaN-sapphire substrate by XRD show single phase InN(0002) peaks with full width half maximum (FWHM) around 400 arcsec. Infrared reflectance spectroscopy is used to analyze the plasmon frequencies, high frequency dielectric constants, the free carrier concentrations and carrier mobilities in these layers. For nominal undoped InN layers, free carrier concentrations in the mid 1019 cm−3 and mobilities around 600 cm−2-V-1-s-1 are observed. Further improvements are expected as the growth parameters are optimized. The explored growth parameters are close to of those employed for GaN growth conditions, which is a major step towards the fabrication of indium rich (Ga1−y−xAlyInx)N alloys and heterostructures.

Properties of InN grown by High-Pressure CVD

AbstractGroup III-nitride compound semiconductors (e.g. AlN-GaN-InN) have generated considerable interest for use in advanced optoelectronic device structures. The fabrication of multi-tandem solar cells, high-speed optoelectronics and solid state lasers operating at higher energy wavelengths will be made possible using (Ga1-y-xAlyInx)N heterostructures due to their robustness against radiation and the wide spectral application range. To date, the growth of indium rich (In1-xGax)N films and heterostructures remains a challenge, primarily due to the large thermal decomposition pressures in indium rich group III-nitride alloys at the optimum growth temperatures. In order to control the partial pressures during the growth process of InN and related alloys, a unique high-pressure chemical vapor deposition (HPCVD) system with integrated real-time optical monitoring capabilities has been developed. We report initial results on InN layers grown at temperatures as high as ∼850°C with reactor pressures around 15 bar. Such process conditions are a major step towards the fabrication of indium rich group III-nitride heterostructures that are embedded in wide band gap group III-nitrides. Real-time optical characterization techniques are applied in order to study the gas phase kinetics and surface chemistry processes during the growth process.For an ammonia to TMI precursor flow ratio below 500, multiple phases with sharp XRD features are observed. Structural analysis perform by Raman scattering techniques indicates that the E2 high mode improves as NH3:TMI ratio is decreased to below 500. Optical characterization of these InN layers indicates that the absorption edge shifts from down from 1.85 eV to 0.7 eV. This shift seems to be caused by a series of localized absorption centers that appear as the indium to nitrogen stoichiometry varies. This contribution will correlate the process parameters to results obtained by XRD, Raman spectroscopy and optical spectroscopy, in order to assess the InN film properties.

Real-time optical monitoring of gas phase dynamics for the growth of InN at elevated pressures

ABSTRACTThe request for increased performance in high-power / high-frequency optoelectronic devices requires new methods for the fabrication of high quality III nitride alloys that exhibit large thermal decomposition pressure such as InN and related materials. To extend the process and growth window towards elevated pressures, a high-pressure CVD system with integrated real time optical characterization techniques has been constructed. The built-in real-time monitoring techniques allow the characterization of gas flow dynamics, precursor decomposition kinetics, as well as the monitoring of the crucial steps of nucleation and film formation. The gas flow dynamics has been characterized and the process parameter are obtained under which the thin film growth process can be maintained under laminar flow condition. Laser light scattering (LLS) has been proven as the most robust optical tool to characterize the onset of turbulence.

High-pressure plasma CVD for high-quality amorphous silicon

The growth rate of device grade amorphous silicon can be increased up to ∼7 Å/s by using high-pressure plasma CVD (∼5 Torr). Control of the electrode gap is important for utilizing high-pressure plasma. The narrowest possible gap, below which plasma becomes unstable, is the best in order to obtain high growth rates from the high-pressure plasma sticking to cathodes. The suppression of higher silane-related radicals is probably responsible for preserving the good quality at the high growth rates because of lower electron temperature in the high pressure and shorter residence time due to the small plasma space.

A dimensionless number for CVD processes: LPCVD versus HPCVD

A dimensionless number is derived which represents the extent to which diffusion affects crystal growth in terms of variables that can be manipulated for the crystal growth. A restriction here is that the result is applicable to processes for which the boundary-layer model is valid, as in the typical horizontal CVD processes. The result is used to critically examine the low pressure CVD process (LPCVD) used for uniform deposition of crystal layers. It is shown that an LPCVD process does not always yield uniform deposition and that a high pressure CVD (HPCVD) in which the total pressure is higher than atmospheric pressure should be used in some cases rather than an LPCVD process if the total pressure is to be manipulated for the uniform deposition. Further, even when an LPCVD process is warranted, the total pressure should be kept as high as possible in some cases for uniform deposition within a certain pressure range. The factor that determines the choice of the total pressure is the apparent order of the growth rate with respect to the total pressure, the choice being dependent on whether or not the order is greater than one-half. No advantage can be gained if the order is one-half. The dimensionless number can also be used to specify growth conditions under which “intrinsic” growth rate data can be generated.