Intrinsic CVD Research Articles

Alpha-voltaic battery on diamond Schottky barrier diode

A diamond Schottky alpha-voltaic nuclear battery (DSAB) is fabricated, and the alpha-particle degradation test is performed. The device is formed on oxygen-terminated intrinsic CVD diamond epitaxially grown on B-doped HPHT diamond. An open-circuit voltage of 1.13 V and a short-circuit current of 53.4 pA are measured under a low-activity alpha source with 8.85 μCi/cm2 irradiation, and a total conversion efficiency of 0.83% is obtained. The DSAB simultaneously has better open-circuit voltage and short-circuit current stability than Si and SiC diodes, which means that DSAB has the highest potential for achieving high and stable conversion efficiency.

Charge multiplication effect in thin diamond films

Herein, we report on the enhanced sensitivity for the detection of charged particles in single crystal chemical vapour deposition (scCVD) diamond radiation detectors. The experimental results demonstrate charge multiplication in thin planar diamond membrane detectors, upon impact of 18 MeV O ions, under high electric field conditions. Avalanche multiplication is widely exploited in devices such as avalanche photo diodes, but has never before been reproducibly observed in intrinsic CVD diamond. Because enhanced sensitivity for charged particle detection is obtained for short charge drift lengths without dark counts, this effect could be further exploited in the development of sensors based on avalanche multiplication and radiation detectors with extreme radiation hardness.

Adsorption of fetal bovine serum on H/O-terminated diamond studied by atomic force microscopy

We investigate adsorption of fetal bovine serum (FBS), a crucial component for cell growth, on intrinsic CVD mono-crystalline diamond with hydrogen and oxygen surface terminations. The surface terminations are prepared by oxygen and hydrogen plasma process. The FBS adsorption is done by immersing diamond into McCoy's 5A medium supplemented with 15% FBS for 10 s–24 h. After rinsing the samples are characterized in the McCoy's medium and for comparison also in air by atomic force microscopy (AFM). By optimized measurements of AFM topography in oscillating regime and by using advanced AFM regimes such as phase imaging, nanoshaving, and force spectroscopy we characterize FBS thickness, adhesion, conformation and selectivity on the H/O-diamond surfaces. We find that FBS is adsorbed in about the same monolayer thickness (2–4 nm) on both H/O-diamond surfaces, yet the protein conformation is different. We present a schematic model.

Thermoluminescent properties of CVD diamonds for radiation protection and radiotherapy applications

AbstractThermoluminescent properties of intrinsic CVD diamond samples synthesized with oxygen added in the gas phase during crystal growth were investigated. Sensitivity and linearity were evaluated over the 0.2–45 Gy dose range, using Cs‐137 and Co‐60 γ‐ray sources. Extremely high sensitivity was observed at doses exceeding 1 Gy, and poor reproducibility, the signal saturating at doses above 10 Gy. The TL properties of the studied crystals were improved by an annealing procedure (400 °C over 30 minutes) but with a significant decrease of the signal amplitude. The annealed detectors were very sensitive to radiation at doses exceeding 2 Gy and signal saturation was observed at doses above 25 Gy. A “quenching” effect of heating rate on the position and the amplitude of the dosimetric peak was also observed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Development of a TOF measurement system of charge carrier dynamics in diamond thin films using a UV pulsed laser

A fast TOF measurement system with 150 ps time resolution for transport behavior of free charge carriers in an intrinsic diamond film by using a UV pulsed laser was developed. The 213 nm UV laser light narrowed to approximately 80 μm widths could locally create hole–electron pairs in selected locations on a diamond film between two parallel electrodes on the surface. This system measured accurate charge transport characteristics in a diamond film, because created charge carriers moved in a part of the diamond film where they did not get any influence from the laser irradiation. Diamond samples used for verification of the TOF system were intrinsic CVD diamond films with thickness between 4 and 10 μm grown on HP/HT diamond substrates. Transit time of holes for one diamond film was 4.7 ns with a traverse distance of 250 μm. The local irradiation of laser made it possible to measure transport characteristics of electrons and holes separately. In addition, it substantially reduced the influence of photoelectron, because the laser beam did not irradiate electrodes. Through several examinations, excellent reliability of the TOF system was confirmed.

Redox-couple interactions with undoped single crystalline CVD diamond

Intrinsic CVD diamond is well known as insulator, however if the surface is hydrogen terminated, a surface conduction can be detected if exposed to air and covered by an adsorbate layer. In this paper we show that hydrogen terminated intrinsic single crystalline CVD diamond undergoes an insulator metal transition if immersed into redox electrolyte solutions with chemical potentials below the valence-band maximum. We have applied cyclic voltammetry experiments using different redox couples to characterize this phenomenon. The experiments reveal a large chemical window (> 4.6 V) of undoped diamond. We detect the same formal potentials as reported in the literature for H-terminated boron doped polycrystalline diamond. The peaks show comparable symmetries but are shifted towards higher and lower potentials, and are significantly broadened. We attribute this to the rate limited electron transfer at the interface. The results are discussed based on the transfer doping model.

Mechanism of photoconductivity in intrinsic epitaxial CVD diamond studied by photocurrent spectroscopy and photocurrent decay measurements

We report experimental results on photocurrent spectra and the transient decay of photocurrent in intrinsic CVD diamond films grown homoepitaxially on natural, (100) oriented, single crystal type IIa diamond substrates. The detectors fabricated from these layers were developed in the frame of the LYRA project (the LYman-alpha RAdiometer onboard the European satellite PROBA-2) and will be used in space for UV solar monitoring. The typical photosensitivity is about 10 −2 A/W at 200 nm and 10 −6 A/W at 300 nm; the typical response time well below 0.1 ms. The enhance in photosensitivity, related to defects in CVD diamond layer and accompanied by long, non-exponential tails in photocurrent transients (persistent photocurrent), is observed in some detectors. The enhancement in photosensitivity also correlates with a long effective lifetime of photo-excited carriers. New defects at about 3.8 eV and another at about 4.3 eV are observed in the photocurrent spectrum of the sample with enhanced photosensitivity.

Photoconductivity of CVD diamond under bandgap and subbandgap irradiations

We systematically studied the photoconductivity of nominally intrinsic diamond films grown by two CVD methods. In the 200–275 nm wavelength range covering the bandgap energy (5.5 eV or 225 nm), the measured photocurrent showed characteristic behavior that can be quantitatively related to a fast recombination of electrons and effective trapping of holes, mainly by trap states near the valence band edge. In addition to photoconductivity, thermoelectric emission spectroscopy and thermally stimulated current measurements were made. From the results, the density and location of two distinctive trap levels within the energy bandgap was estimated. The results are not only self-consistent, but also agree with other authors' findings, such as a hole-dominated current, without or under bandgap illumination, a Fermi level close to the valence band edge, an electron recombination center in the middle of the bandgap, and a shallow hole-trap state having an extremely high density of ∼ 1019 cm−3. Based on these data, we suggest a bandgap and trap-state model for intrinsic CVD diamond. The details of this model and the characteristic properties of the defects/traps are consistent with experimental results and theoretical findings made by other authors covering a large diversity of areas, such as photoluminescence and cathodoluminescence, photoabsorption, carrier lifetimes and mobilities, electron paramagnetic resonance, cold-cathode electron emission, and photoconductive current switching.