Robert Chodelka

High-pressure process to produce GaN crystals

High melt temperature and thermal decomposition prevent the use of standard bulk semiconductor crystal growth processes for the production of GaN. We have employed a hydrostatic pressure system to grow GaN crystals. An ultrahigh pressure, high temperature process was developed using a solid-phase nitrogen source to form GaN crystals in a Ga metal melt. Using a thermal gradient diffusion process, in which nitrogen dissolves in the high temperature region of the metal melt and diffuses to the lower temperature, lower solubility region, high quality crystals up to ∼1 mm in size were formed, as determined by scanning electron microscopy, x-ray diffraction, and micro-Raman analysis.

GaN films annealed under high pressure

Abstract We present in this manuscript the results of a comparison study between MOCVD-grown GaN films annealed in a novel high-pressure annealing furnace and those annealed in a conventional tube furnace under flowing argon gas at similar temperatures for similar times. Atomic force microscopy, scanning electron microscopy, X-ray diffraction, photoluminescence and cathodoluminescence were used to investigate the affects of the high-pressure anneals in comparison to those which were annealed with the more conventional method. We demonstrate that high pressure annealing has successfully prevented the degradation of GaN films at high temperatures.

Preparation and characterization of barium titanate electrolytic capacitors by anodic oxidation of porous titanium bodies

Low-temperature (50-60 degrees C) anodic oxidation of porous titanium bodies in an aqueous electrolyte containing Ba/sup 2+/ in solution has been used to infiltrate BaTiO/sub 3/ onto a large surface area. Microstructural and dielectric characterization indicates the possibility of achieving extremely high capacitance values by further improving the porosity of the Ti bodies and electroding the BaTiO/sub 3/ surface using electroless plating techniques.<<ETX>>

Crystal growth of gallium nitride and manganese nitride using an high pressure thermal gradient process

Abstract Standard, semiconductor-industry bulk crystal growth processes are virtually impossible for the production of GaN as this is prohibited by both the high melt temperature of GaN and thermal decomposition of the compound into Ga metal and diatomic nitrogen gas. In this study, a novel hydrostatic pressure system was employed to grow GaN crystals in a very high pressure ambient. The ultra-high pressure, high temperature process uses a solid-phase nitrogen source to form GaN crystals in a metal alloy melt. Using a thermal gradient diffusion process, in which nitrogen dissolves in the high temperature region of the metal melt and diffuses to the lower temperature, lower solubility region, high quality crystals up to ∼0.5 mm in size were formed, as determined by scanning electron microscopy, X-ray diffraction, and micro-Raman analysis.