Tatyana I. Feygelson

Fabrication and characterization of two-dimensional photonic crystal microcavities in nanocrystalline diamond

Diamond-based photonic devices offer exceptional opportunity to study cavity QED at room temperature. Here we report fabrication and optical characterization of high quality photonic crystal (PC) microcavities based on nanocrystalline diamond. Fundamental modes near the emission wavelength of negatively charged nitrogen-vacancy (N-V) centers (637 nm) with quality factors (Qs) as high as 585 were observed. Three-dimensional Finite-Difference Time-Domain (FDTD) simulations were carried out and had excellent agreement with experimental results in the values of the mode frequencies. Polarization measurements of the modes were characterized; their anomalous behavior provides important insights to scattering loss in these structures.

Reduced Self-Heating in AlGaN/GaN HEMTs Using Nanocrystalline Diamond Heat-Spreading Films

Nanocrystalline diamond (NCD) thin films are deposited as a heat-spreading capping layer on AlGaN/GaN HEMT devices. Compared to a control sample, the NCD-capped HEMTs exhibited approximately 20% lower device temperature from 0.5 to 9 W/mm dc power device operation. Temperature measurements were performed by Raman thermography and verified by solving the 2-D heat equation within the device structure. NCD-capped HEMTs exhibited 1) improved carrier density <i>NS</i>, sheet resistance <i>R</i>_SH; 2) stable Hall mobility μ<i>H</i> and threshold voltage <i>VT</i>; and 3) degraded on-state resistance <i>RON</i> , contact resistance <i>RC</i>, transconductance <i>Gm</i>, and breakdown voltage <i>V</i>_BR.

Ultrathin single crystal diamond nanomechanical dome resonators.

We present the first nanomechanical resonators microfabricated in single-crystal diamond. Shell-type resonators only 70 nm thick, the thinnest single crystal diamond structures produced to date, demonstrate a high-quality factor (Q ≈ 1000 at room temperature, Q ≈ 20 000 at 10 K) at radio frequencies (50-600 MHz). Quality factor dependence on temperature and frequency suggests an extrinsic origin to the dominant dissipation mechanism and methods to further enhance resonator performance.

Thermal conduction inhomogeneity of nanocrystalline diamond films by dual-side thermoreflectance

Thin diamond films of thickness near 1 μm can have highly nonuniform thermal conductivities owing to spatially varying disorder associated with nucleation and grain coalescence. Here, we examine the nonuniformity for nanocrystalline chemical vapor deposited diamond films of thickness 0.5, 1.0, and 5.6 μm using picosecond thermoreflectance from both the top and bottom diamond surfaces, enabled by etching a window in the silicon substrate. The extracted local thermal conductivities vary from less than 100 W m−1 K−1 to more than 1300 W m−1 K−1 and suggest that the most defective material is confined to within 1 μm of the growth surface.

Fabrication of short-wavelength photonic crystals in wide-band-gap nanocrystalline diamond films

Nanocrystalline diamond films and e-beam patterning techniques have been used to fabricate visible to near-infrared photonic slab crystals (PhCs) with deep submicron feature sizes. Two methods of fabrication, both based on electron-beam lithography, have been explored and are detailed in this Communication. The first method uses direct patterning of flowable oxide as a hard mask for a subsequent highly anisotropic oxygen plasma reactive ion etching of the nanocrystalline diamond film. The second method involves image inversion and employs an organic-inorganic bilayer resist structure that planarizes the surface and provides for a well-controlled undercut. The subsequent metal evaporation and lift-off creates a metal mask with 100nm features demonstrating fine control over edge roughness that is not compromised by the nanocrystalline roughness of the diamond film. Chromium etch mask and oxygen plasma were used to fabricate the diamond PhC. With the proper choice of metal mask and reactive ion etch, this te...

Optical Absorption, Depolarization, and Scatter of Epitaxial Single-Crystal Chemical-Vapor-Deposited Diamond at 1.064 μm

Epitaxial single-crystal chemical-vapor-deposited diamond with (100) crystal orientation is obtained from Element Six (Ascot, United Kingdom) and Apollo Diamond (Boston, Massachusetts). Both companies supply 5×5-mm squares with thicknesses of 0.35 to 1.74 mm. Element Six also provides disks with a state of the art diameter of 10 to 11 mm and a thickness of 1.0 mm. The absorption coefficient measured by laser calorimetry at 1.064 μm is 0.003 cm -1 for squares from Element Six and 0.07 cm -1 for squares from Apollo. One Apollo specimen has an absorption coefficient near those of the Element Six material. Absorption coefficients of Element Six disks are 0.008 to 0.03 cm -1 . Each square specimen can be rotated between orientations that produce minimum or maximum loss of polarization of a 1.064-μm laser beam transmitted through the diamond. Minimum loss is in the range 0 to 11% (mean=5%) and maximum loss is 8 to 27% (mean=17%). Element Six disks produce a loss of polarization in the range 0 to 4%, depending on the angle of rotation of the disk. Part of the 0.04 to 0.6% total integrated optical scatter in the forward hemisphere at 1.064 μm can be attributed to surface roughness.

Anisotropic and inhomogeneous thermal conduction in suspended thin-film polycrystalline diamond

While there is a great wealth of data for thermal transport in synthetic diamond, there remains much to be learned about the impacts of grain structure and associated defects and impurities within a few microns of the nucleation region in films grown using chemical vapor deposition. Measurements of the inhomogeneous and anisotropic thermal conductivity in films thinner than 10 μm have previously been complicated by the presence of the substrate thermal boundary resistance. Here, we study thermal conduction in suspended films of polycrystalline diamond, with thicknesses ranging between 0.5 and 5.6 μm, using time-domain thermoreflectance. Measurements on both sides of the films facilitate extraction of the thickness-dependent in-plane ( κr) and through-plane ( κz) thermal conductivities in the vicinity of the coalescence and high-quality regions. The columnar grain structure makes the conductivity highly anisotropic, with κz being nearly three to five times as large as κr, a contrast higher than that report...

Low temperature internal friction in nanocrystalline diamond films

Measurements of the temperature dependence of the internal friction and frequency of three nanocrystalline diamond films grown on silicon oscillator substrates indicate that the mechanical properties of the films are dominated by their interface layers. The films, with thicknesses of 0.3, 0.6, and 1.14μm, were measured between 0.4K and room temperature and have low temperature (below 10K) internal frictions between 2×10−6 and 5×10−6, which is an order of magnitude lower than has been reported previously. Additionally, all films display an internal friction peak at approximately 1.7K. The shear modulus of the films, 545–551GPa, is comparable to that for single-crystal diamond.

Bunch characteristics of an electron beam generated by a diamond secondary emitter amplifier

Electron bunches for high performance free electron lasers are subject to constraints on charge per bunch and pulse shape. A Diamond secondary emitter used in conjunction with a photocathode and drive laser has potential to enable a high brightness, high peak current photoinjector by increasing the effective quantum efficiency of the photocathode. A theoretical characterization of the bunches so produced has been heretofore absent. Using a combination of Monte Carlo and analytical models, the shape of the bunches, their transit time, and emission time constants are determined and shown to be sensitive to the accelerating field in the diamond flake, incident beam profile, doping, and surface conditions. Methods to allow for extension to regimes of technological interest in terms of diamond thickness, external field, and primary pulse shape are given.

Nanocrystalline diamond films as UV-semitransparent Schottky contacts to 4H-SiC

A heterojunction between thin films of nanocrystalline diamond (NCD) and 4H-SiC has been developed. Undoped and B-doped NCDs were deposited on both n− and p− SiC epilayers. I-V measurements on p+ NCD∕n− SiC indicated Schottky rectifying behavior with a turn-on voltage of around 0.2V. The current increased over eight orders of magnitude with an ideality factor of 1.17 at 30°C. Ideal energy-band diagrams suggested a possible conduction mechanism for electron transport from the SiC conduction band to either the valence band or acceptor level of the NCD film. Applications as an UV semitransparent electrical contact to 4H-SiC are discussed.