Minglong Zhang

Infrared optical properties of diamond films and electrical properties of CVD diamond detectors

In this paper, the infrared optical properties of diamond films grown on silicon substrates by means of the microwave plasma chemical vapour deposition (MPCVD) method were first studied by infrared spectroscopic ellipsometry in the photo energy range of 0.1–0.4 eV. Using the effects of annealing treatment on the extinction coefficient k and refractive index n of diamond films, the infrared optical quality of the diamond film can be significantly improved by thermal annealing treatment in N2 atmosphere. After annealing the value of k was about 10−12–10−15. However, for the non-annealed diamond film, the value of k varied in a large range, about 10−3–10−14. After annealing the refractive index n of the diamond film increased and was close to that of a single crystal, Type IIa natural diamond. The graphite on the diamond surface can be removed to some extent after surface oxidizing treatment of the diamond film in a solution of H2O2 and H2SO4, which causes the obvious decrease of the leakage current of the CVD diamond detector. Based on these diamond films, diamond x-ray detectors with a response time of about 3 ns were fabricated. From the temperature behaviour and the time response of the CVD diamond detector to x-ray irradiation, we find that the various defects or impurities that exist in the film may be responsible for the long fall time.

The electrical properties of diamond-like carbon film/D263 glass composite for the substrate of micro-strip gas chamber

Abstract Micro-Strip Gas Chamber (MSGC) used as a position sensitive gas detector has perfect performances in the detection of X-ray, α particles, β particles, γ-ray and other nuclear irradiations. However, it encounters a severe problem, that is, positive charge accumulation which can be avoided by reducing the surface resistivity of insulating substrate. So, diamond-like carbon (DLC) film is deposited on D263 glass to modify its electrical properties as substrate for MSGC. DLC film has optical smoothness and strong adhesive force on D263 glass, which helps fabricate microelectrodes on it. Raman spectroscopy demonstrates that DLC film is of sp3 and sp2 bonds corresponding to the occupied bonding (σ) states and the empty antibonding (σ*) states, and therefore it is a type of electronically conducting material. I–V plots indicate that three samples enjoy very steady resistivities between 109 Ω cm and 1012 Ω cm, especially the DLC film under high electrical field over 104 V cm−1, which meet the optimum requirements of MSGC. DLC film/D263 glass composite substrate is essential for MSGC to avoid charge-up.

An ellipsometric analysis of CVD-diamond films at infrared wavelengths

The ellipsometric measurements of diamond films, which were deposited onto polished [100]-oriented silicon and rough alumina ceramic substrates by hot filament chemical vapor deposition (HFCVD) technique, have been performed over the spectral range from 3 to 12 μm. The parameters of the films, namely, film thickness and volume fraction for each constituent have been calculated from the ellipsometric data by the best fitting procedure using the optimized model. A two-layer stack with about 870-nm thick surface rough layer on top of diamond basis can be perfectly used to simulate the films on silicon substrates. However, the films on alumina substrates cannot be well described by the two-layer model. For the sake of good fit, a three-component interface layer, which consists of 64.13±4% alumina, 23.34±3% diamond and 12.53±1% void, must be appended to the model by Bruggeman effective medium approximation.

The influence of deposition conditions on the dielectric properties of diamond films

In this letter, with the aim of optimizing the growth conditions of diamond films on carbon ions implanted in alumina ceramic substrates by the hot filament chemical vapour deposition method using a gaseous mixture of alcohol and hydrogen, the dielectric constants of diamond films deposited under different conditions are determined by infrared spectroscopic ellipsometry in the spectral range of 2.5–12.5 µm. Results show that diamond films with low dielectric constant can be obtained under lower alcohol concentration and higher substrate temperature. Under an alcohol concentration of 0.8% and a substrate temperature of 850 °C, the dielectric constant and the thermal conductivity of the diamond film/alumina composite, with a diamond film of 100 µm thickness, are 6.5 and 3.98 W cm−1 K−1, respectively.

Spectroscopic ellipsometric study of CVD diamond films: modelling and optical properties in the energy range of 0.1–0.4 eV

In this paper, the infrared optical properties of diamond films on silicon substrates grown by means of hot filament chemical vapour deposition (HFCVD) and microwave plasma chemical vapour deposition (MPCVD) method, are studied by infrared spectroscopic ellipsometry (IRSE) in the energy range of 0.1–0.4 eV. The establishment of appropriate models has the strongest influence on the fit of ellipsometric spectra. For diamond films grown by HFCVD method, the best fitting model is Si|diamond| (diamond + void)| air with an 879 nm rough surface layer included by Bruggeman EMA, but for MPCVD film with a 77.5 nm middle layer of SiO2. The average refractive index n of the HFCVD film is about 2.19 and the extinction coefficients k are between 1.0 and 10−3. However, for the MPCVD film, the value of n is very close to that of natural diamond and the k values are about 10−12–10−15, which show that the film grown by MPCVD is transparent in infrared region, and is optically much better than the HFCVD film.

Development of MSGC detectors on diamond film-coated silicon composite substrates

In this paper, diamond film-coated silicon was developed to be used as a substrate in a microstrip gas chamber (MSGC) for the first time. The roughness of the composite substrate was rather low, and the resistivity was in the range of 1010?1011??cm. Its capacitance was very small and almost had no variation with frequency. All these results prove that the diamond film/Si composite material is a promising substrate for MSGCs. Using this composite substrate, a MSGC detector with an area of 2 ? 2?cm2 was fabricated. The effects of the drift voltage and cathode voltage on the energy resolution for 5.9?keV 55Fe x-rays have been examined in detail and discussed. An energy resolution (the relative full width at half maximum of the x-ray peak) of 12.3% was achieved when the MSGC was operated at a drift voltage of ?1000?V and a cathode voltage of ?650?V with a gas mixture (90% Ar + 10% CH4).

Preparation and characterization of [100]-oriented diamond films by HFCVD

In this paper we report high quality [100]-oriented diamond films prepared by HFCVD using hydrogen as carrier gas and C2H5OH as carbon source for the first time. The surface morphology observed by SEM showed polycrystalline diamond films with [100] faced structure with an average grain size of ~20 μm. The Raman spectrum indicated sp3 bonding with a sharp peak at 1333 cm-1. The I-V characteristics obtained via Au contact were determined by semiconductor characterization system. The electrical resistivity of HFCVD [100]-oriented diamond film was ~3.0x1010Ω cm. The capacitance and dielectric loss of films were very small with the value of 2.0pF and 0.02, respectively, and almost had no dependence with the change of frequency in high frequencies.

Energy resolution in x-ray detecting microstrip gas chamber fabricated on CVD diamond films

The valuable properties of CVD diamond films used as micro-strip gas chamber (MSGC) substrate are presented and a gas detector with an area of 20x20mm2 was fabricated on a CVD diamond film whose resistivity ranges between 1010 and 1011Ω-cm. We systematically report the energy spectra generated by a 5.9keV55Fe X-ray source. The effects of high potential on the energy resolution are investigated and discussed in detail. A better energy resolution about 12.2% is obtained when MSGC filling with an argon+10%CH4 gas mixture operated at a drift potential of -1100V and a cathode voltage of -650V.

Effects of deposition conditions and annealing process on the infrared optical properties of diamond films grown by MPCVD

The effects of deposition conditions and annealing process on the optical properties of diamond films on silicon substrate grown by MPCVD method are investigated by infrared spectroscopic ellipsometry (2.5-12.5μm). Results indicate that the low nucleation temperature will be in favor of decreasing the infrared absorption at 3.5μm. The refractive index n of diamond films deposited under higher growth temperature will fluctuate weakly. After annealing in N2 atmosphere an obvious improvement of the infrared optical properties is also found. After annealing the value of k was about 10-12~10-15. However, for non-annealed diamond film, the value of k was about 10-3~10-14. After annealing the refractive index n increased and was close to that of single crystal Type IIa natural diamond.

Charge collection properties of 1x128 array radiation detector based on CVD diamond film

CVD diamond film has many excellent features, which promotes its potential application in radiation detection. In this paper, one kind of 1x128 array detector was developed by using a free-standing (100) textured CVD diamond film with a thickness of 300µm. The charge collection efficiencies (η) and distances (d) of the detector were investigated by using 241Am α particles (5.5MeV), 60Co γ-rays (1.25MeV), 55Fe X-rays (5.9KeV), resulting that the CVD diamond detector boasts high η (>38%) and d (>115µm), among which the η and d of X-ray reaches 41.70% and 125µm, respectively.