Beibei Gu

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.

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.

Optimization for the growth of CVD diamond on Al2O3 and the response to alpha particle irradiation

A diamond film was grown on alumina ceramic by micro-wave plasma chemical vapor deposition (MPCVD) and was fabricated into an interdigited alpha-particle detector. By optimizing growth parameters in MPCVD, we found that under the conditions with carbon source (alcohol/hydrogen) concentration in 0.8% and deposition temperature at 850°C, the least content of sp2 and the best quality of diamond film could be obtained. Photocurrent under α-particle irradiation was in the range of 10-5~10-4A within one hundred voltages, and dark current was about 10-9~10-8A.