We developed a process to fully hydrogen-terminate diamond by annealing in forming gas. The surface was characterized using circular transmission line measurements (CTLMs) to evaluate the onset and degree of hydrogen termination. No hydrogenation occurred at temperatures at or below 500 °C. Hydrogenation occurs after annealing for 5 min at temperatures between 600 and 1000 °C, with complete hydrogenation achieved at 1000 °C, which showed the same sheet resistance as diamond terminated in a hydrogen plasma. Annealing at temperatures lower than 1000 °C resulted in only partial hydrogenation but can be compensated by increasing the anneal time. At temperatures exceeding 1100 °C, the sheet resistance suddenly and drastically increases, indicating instability of a hydrogen-terminated diamond surface at elevated temperatures under forming gas. The activation energy was determined to be 1.20eV. SEM inspection showed that annealing in hydrogen produced significantly reduced surface roughness compared to diamond surfaces hydrogenated in a H2 plasma.

In this work, we present the theory and modeling framework of a diamond optically gated junction field-effect transistor (DOGFET). The device utilizes nitrogen substitutional centers in type-1b diamond to optically modulate a p- boron doped diamond channel. Using sub-gap lasers with intensities as low as 100 W/cm ${}^2$, electrons are optically excited from substitutional nitrogen sites to the conduction band of the diamond substrate, thus enabling the optical gate to exercise control on modulating the space-charge region at the junction and therefore the channel conductivity. We show that the device can deliver a current of 7 $\mathrm{\mu A}/\mathrm{\mu }$m, or equivalently 1750 A/cm ${}^2$, while switching at a frequency greater than 100 kHz, in a form factor of 5 ${\mathrm{\mu m}}^2$. The breakdown voltage is found to be greater than 1850 V, with a breakdown field strength of $\sim$13 MV/cm. Moreover, the device supports nonvolatile operation with a “memory effect” enabling single transistor state retention. The presented simulation framework provides a physically grounded insight into the limits and opportunities of optoelectronic diamond systems.

In this study, the growth of high-quality graphite single crystals from a molten metal flux at atmospheric pressure was optimized. The crystals were precipitated from a saturated iron-carbon solution by slowly cooling (4 °C/h) from a maximum temperature to reduce the carbon solubility. The graphite flakes were >25 square millimeters in area and >10 of microns thick, with individual crystal grains as large as 1.2 mm2. The crystals were (0002) oriented, as determined by x-ray diffraction. The high structural quality of the graphite crystals was verified by Raman spectroscopy. For graphite with the natural distribution of carbon isotopes, the G-peak at 1580 cm-1 was narrow (~12 cm-1) and the defect peak (D-peak) was absent. To demonstrate the process versatility, graphite crystals enriched in the 13C isotope were grown. The Raman peak shifted to 1520 cm-1 for graphite crystals en-riched to 99% 13C. The etch densities from defect sensitive etching ranged from 0 to 1.6x108 etch pits per cm2. The process was refined by examining the crystal size and quality as functions of the carbon concentration in the starting sources, the carrier gas composition, and maximum temperature. The simplicity of this process suggests it can be scaled to produce very large graphite crystals that would be suitable for a wide range of technologies.

In this study, the growth of high-quality graphite single crystals from a molten metal flux at atmospheric pressure was optimized. The crystals were precipitated from a saturated iron–carbon solution by slowly cooling (4 °C/h) from a maximum temperature to reduce the carbon solubility. The graphite flakes were >25 square millimeters in area and >10 microns thick, with individual crystal grains as large as 1.2 mm². The crystals were (0002) oriented, as determined by X-ray diffraction. The high structural quality of the graphite crystals was verified by Raman spectroscopy. For graphite with the natural distribution of carbon isotopes, the G-peak at 1580 cm⁻¹ was narrow (~12 cm⁻¹) and the defect peak (D-peak) was absent. To demonstrate the process versatility, graphite crystals enriched in the ¹³C isotope were grown at 5 degrees of enrichment. The Raman G-peak linearly shifted from 1580 cm⁻¹ to 1520 cm⁻¹ for graphite crystals enriched from 1 to 99% ¹³C. The etch pit densities from defect-sensitive etching ranged from 0 to 1.6 × 10⁸ per cm². The process was refined by examining the grain size and quality as functions of the carbon concentration in the starting sources, the carrier gas composition, and maximum temperature. The simplicity of this process suggests it can be scaled to produce very large graphite crystals that would be suitable for a wide range of technologies.