Bradley A. Fox

Diamond devices and electrical properties

Abstract Diamond offers tremendous potential for electronic applications such as field effect transistors. An investigation of the electrical properties of boron-doped homoepitaxial diamond films and the metal-oxide-diamond gate structure was performed. Additionally, field effect transistors were fabricated and characterized. Improvements in the diamond deposition process produced boron-doped homoepitaxial diamond films where the room temperature Hall mobility exceeded 1000 cm 2 V −1 s −1 . Analysis of the temperature-dependent carrier concentration indicated that the compensation was 15 cm −3 . The gate structure for metal-silicon dioxide-boron-doped diamond field effect transistors was evaluated by current-voltage and capacitance voltage measurements. Good correlation of the uncompensated acceptor concentration, determined by capacitance-voltage measurements, and the boron concentration, determined by secondary ion mass spectroscopy, was attained. Preliminary measurements suggested that the density of interface states for this structure was ≈ 10 12 cm −2 eV −1 . Field effect transistors exhibited saturation and pinch-off at temperatures as high as 773 K. The highest normalized transconductance measured was 1.3 mS mm −1 . The field effect transistors were combined into analogue and digital circuits that operated at 523 K and 673 K, respectively.

Comparison of the electrical properties of simultaneously deposited homoepitaxial and polycrystalline diamond films

The electrical transport properties of simultaneously deposited, B‐doped homoepitaxial and polycrystalline diamond thin films have been evaluated by Hall‐effect and resistivity measurements over a temperature range of 80–600 K. The same films were later characterized by scanning electron microscopy, secondary‐ion‐mass spectroscopy, and an oxidation defect etch. The study involved four sets of chemical‐vapor‐deposited diamond films with individual B concentrations ranging from 1.5×1017 to 1.5×1020 cm−3. In each of the four cases the mobility of the polycrystalline film was lower than that of the homoepitaxial film by 1–2 orders of magnitude over the entire temperature range. Polycrystalline films also incorporated 2–4 times more B, had 3–5 times higher compensation ratios, and displayed activation energies that were 0.05–0.09 eV lower than in the homoepitaxial films. Hopping conduction was observed in both types of films at low temperatures, but was enhanced in polycrystalline films as evident by higher tr...

Comparison of electronic transport in boron‐doped homoepitaxial, polycrystalline, and natural single‐crystal diamond

Hall‐effect and resistivity measurements were performed on simultaneously deposited B‐doped homoepitaxial and polycrystalline diamond films, as well as a (100)‐oriented type‐IIb natural diamond crystal, over a temperature range of 140–600 K. At 298 K, the respective Hall mobilities for the homoepitaxial and polycrystalline films were 519 and 33 cm2/V s, while the active carrier concentrations were both approximately 2×1014 cm−3. For the natural diamond, a Hall mobility of 564 cm2/V s and a carrier concentration of 2×1013 cm−3 were measured at room temperature. A comparison of the transport behavior of the three specimens indicates that the electronic properties of diamond grown by chemical vapor deposition are potentially of equal or greater quality than natural diamond and that the transport properties of polycrystalline films are severely degraded by the effects of grain boundaries.

Characterization of rectifying contacts on natural type IIb diamond

Metal‐semiconducting diamond (MS) and metal‐insulating diamond‐semiconducting diamond (MIS) contacts were fabricated on the same type IIb single crystal diamond. Direct comparisons of MS and MIS structure characteristics were made by analysis of current‐voltage and differential capacitance‐voltage (C‐V) data. Both the MS and MIS contacts exhibited good rectifying characteristics, with a 5 V rectification ratio ≳106. The depletion layer uncompensated acceptor concentration measured in both structures by C‐V analysis was ∼1.8×1016 cm−3.