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We investigated an effect of interface defects in diamond lateral p-n-junction diodes on their reverse-biased leakage currents. Defects at the p–n interface were observed by cross-sectional transmission electron microscopy from different electron incident directions. The observations revealed that the diodes with the large leakage current had a number of defects localized at the p–n interface. The amount of the defects is related to the magnitude of the reverse leakage currents of the devices. Leakage analysis with applying high voltages strongly suggests that the leakage currents originate from the observed defects. Possible origin of the defect formation is discussed. [ABSTRACT FROM PUBLISHER]

The contact resistance between heavily phosphorus doped n-type (n+-type) diamond (111) layers and graphite electrodes was investigated. To analyze the contact resistance properties in detail in the low-voltage region, the transfer length method including nonlinear terms with a constant current was analyzed based on the double Schottky contact configuration. Using this method, we have revaluated the metal contact resistance reported previously. Using the graphite electrodes, the linearity of current-voltage characteristics was improved. The contact resistance was reduced by a factor of ten compared to that of conventional Ti/Pt/Au electrodes. The graphite electrodes were formed directly by thermal annealing at 1300 °C for 10 min from an n+-type diamond surface. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Reverse characteristics of diamond PiN diodes were studied under high reverse bias for high voltage applications. We have fabricated vertical diamond PiN diode structures consisting of a phosphorus-doped n-type diamond layer and an undoped intrinsic diamond layer on a heavily boron-doped p-type diamond substrate with Au/Pt/Ti Ohmic contacts on both the top and the bottom surfaces. Temperature dependent current-voltage ( I- V) and capacitance-voltage ( C- V) measurements were carried out to reveal the diode characteristics. The fabricated PiN diodes exhibited a sharp and repeatable reverse breakdown with positive temperature dependence indicating an avalanche mechanism. The obtained maximum breakdown field was 2.3 MV cm−1 (920 V) which is comparable to the ideal dielectric breakdown field of SiC. The reverse breakdown field and the leakage current were correlated with the hillock density. This research indicates that robust diamond power devices with high breakdown reliability can be achievable after improvement the quality of the intrinsic layer. [ABSTRACT FROM AUTHOR]

We developed normally-off diamond junction field-effect transistors with narrow channel widths. The p-channel device with the narrowest channel width of 0.26 \mu \textm showed a large threshold voltage of −3 V. The obtained threshold voltage is consistent with the value estimated by considering the tapered channel width and the gradual-doping in the channel, which were measured by secondary ion mass spectrometry and cross-sectional transmission electron microscopy. We confirmed that the threshold voltage can be well controlled by the channel width. [ABSTRACT FROM PUBLISHER]

Blocking characteristics of diamond junction field-effect transistors were evaluated at room temperature (RT) and 200^\circC. A high source-drain bias (breakdown voltage) of 566 V was recorded at RT, whereas it increased to 608 V at 200^\circC. The positive temperature coefficient of the breakdown voltage indicates the avalanche breakdown of the device. We found that the breakdown occurred at the drain edge of the p-n junction between p-channel and the n^+-gates. All four devices measured in this letter showed a maximum gate-drain bias over 500 V at RT and 600 V at 200^\circC. [ABSTRACT FROM PUBLISHER]

High-temperature performance of diamond junction field-effect transistors (JFETs) with lateral p-n junctions is demonstrated. Diamond JFETs fabricated by n-type selective growth can be operated at 723 K, and show very low leakage currents of \sim10^-13~A and high ON/OFF ratios >10^6. Specific on-resistance decreases from 52.2 m\Omega\cdotcm^2 at 300 K to 1.4 m\Omega\cdotcm^2 at 723 K. At high temperatures, the device shows steep subthreshold swings very close to the theoretical limit. The low leakage currents are maintained even at a high drain voltage of -100~V. These excellent properties at high temperatures and high voltage show that diamond JFETs can work in harsh environments. [ABSTRACT FROM PUBLISHER]

A major obstacle limiting diamond electronics is dislocations, which deteriorate device properties. As threading dislocations (TDs) are normally inherited from the substrate to the epitaxial layer, control and annihilation of their propagation are important. Herein, metal‐assisted termination (MAT), in which the propagation of dislocations is suppressed by in situ metal doping, is proposed. Heavy W doping is realized by a hot‐filament (HF) chemical vapor deposition (CVD) using heated wires at a high temperature of >2400‐K. A large reduction of TD density is confirmed by cathodoluminescence studies and etch‐pit analysis. The impact of dislocation reduction is investigated electrically. After insertion of the MAT buffer layer, Schottky barrier diodes (SBDs) show improved rectifying action and highly uniform characteristics even when substrates with high dislocation densities (mosaic and heteroepitaxial wafers) are used. The 3D structure of dislocation propagation is successfully captured by two‐photon‐excited photoluminescence (2PPL) imaging of Band‐A luminescence. The 2PPL Band‐A luminescence (without band‐edge excitation) shows high spatial resolution in the depth direction. An abrupt decrease in TD density is captured for heteroepitaxial substrates with an inserted MAT buffer layer. The MAT technique provides an effective approach to realize high‐performance diamond electronics. [ABSTRACT FROM AUTHOR]

Electron emission plays an important role in diverse applications, from cold cathodes to chemical processes (solvated electrons, water purification), energy generation (thermionic or dye-sensitized solar cells), and even cancer treatment. Here we show that by surface treatment using electrochemically grown polypyrrole the secondary-electron emission and photoelectron emission from boron-doped diamond is enhanced even above the intensity of electron emission from the hydrogen-terminated surface with negative electron affinity. This enhancement is stable in air for at least one month and it persists also in vacuum after thermal annealing. Scanning electron microscopy, Kelvin probe force microscopy, total photoelectron yield spectroscopy as well as surface mapping by Auger and secondary ion mass spectroscopies are used to characterize and correlate the surface electronic and chemical properties. A model of the electron emission enhancement is provided. [Display omitted] • Molecular scale modification enhances electron emission from diamond. • Enhanced electron emission is stable in air and after thermal annealing in vacuum. • Enhancement observed for secondary electrons in electron microscope. • Enhancement observed in photoelectron emission. [ABSTRACT FROM AUTHOR]

We fabricated graphene on atomically flat diamond (111) surfaces via annealing with nickel as a catalyst. The annealing was conducted at 900 °C for 1 min under Ar atmosphere. Using Raman spectroscopy, the formed graphene was characterized as multilayer with some monolayer coverage. After the graphene layers were removed, the diamond (111) surfaces exhibited step-terrace structures with a root-mean-square roughness of 0.05 nm in the terrace region. The step height was ~ 0.21 nm, which agreed well with a single bi-atomic layer of (111) diamond. These results indicate that the graphene layers were formed on atomically flat diamond (111) surfaces with step-terrace structures. The graphene layers showed P-type conduction with sheet carrier concentration and mobility values of 5.7 × 10 13 cm − 2 and 140 cm 2 /Vs, respectively. These electrical properties are equivalent to the band structure properties predicted by density functional theory calculations. [ABSTRACT FROM AUTHOR]