Yiben Xia

Electrical properties of contacts on P-type Cd0.8Zn0.2Te crystal surfaces

Abstract In this paper effects of surface treatments of p-type Cd0.8Zn0.2Te devices were studied by Atomic Force Microscopy (AFM), I–V measurements, and electrical properties as well as different contact technologies using Au, Al, In and electroless Au. It is shown that electroless Au film deposited by the chemical method can form a heavily doped p+ layer on a smooth surface, which is nearly ohmic on p-type material. Electroless Au gives better contact than evaporated Au, Al or In. A post-annealing treatment of electroless Au film improves the ohmic quality of contacts and enhances the adhesion between contact layer and the Cd0.8Zn0.2Te crystal surface.

Growth of p-type ZnO films and fabrication of ZnO photodiode-based UV detectors

In this work, Al–N-co-doped ZnO films were deposited on the smooth nucleation side of a freestanding diamond film by a radio-frequency (RF) reactive magnetron sputtering method. The influence of sputtering atmosphere and substrate temperature on the conduction type of ZnO films was studied. ZnO photodiodes were fabricated by depositing the Al–N-co-doped p-type ZnO films on the Al-doped n-type ZnO films. The ZnO photodiode exhibited the distinct rectifying current–voltage (I–V) characteristics with a turn-on voltage of ~2.0 V. The photodiode was used for UV detector application and the detector showed a significant discrimination between UV and the visible light.

A new passivation method for porous silicon

Abstract In this paper, we show the enhancement and stabilization of the luminescence when depositing diamond-like carbon (DLC) thin films on top of porous silicon (PS) layers. DLC thin films reduce the influence of different ambients to PS, which can cause the desorption of hydrogen molecules from the Si–Hx bonds leaving dangling bonds which operate as non-radiative recombination traps. So DLC thin films can lead to a more stable luminescence from PS layers. At the same time, hydrogenated carbon nitride films can further enhance the photoluminescence efficiency of PS because more dangling bonds are passivated by nitridation.

Infrared optical properties of amorphous hydrogenated carbon nitride film

The microstructure and optical properties of nitrogen-doped hydrogenated carbon DLC:N films deposited by the rf plasma-enhanced chemical vapor deposition (PECVD) method were studied by atomic force microscopy (AFM), Raman, Fourier-transform infrared (FTIR) and infrared ellipsometric (IRE) spectrometry. The absorption intensities of the peaks CNH (1600 cm−1), CN (2200 cm−1) and NH (3250 cm−1) in the IR spectra increase with the N2/CH4 flux ratio. Raman spectra show that the shape of the D and G bands of DLC:N film varies slightly with the increase of N content, which means that the main structures of N-doped films are still diamond-like carbon (DLC). However, four Gaussian decomposition results show that the peak of the G band widens and shifts to the low wavenumber with increased nitrogen content in Raman spectra due to amorphous C3N4 structure being formed in the nitrogen-doped DLC film. AFM topographies and lateral force microscopy (LFM) images of DLC:N film confirm that the amorphous C3N4 exists as particles several tens of nanometers in size in the film. IRE spectral analysis results show that the refractive index of the film in the infrared region (2–14 μm) decreases slightly from 1.8 to 1.6 with increased nitrogen content.

Effect of a buffer layer on the properties of UV photodetectors based on a ZnO/diamond film structure

In this paper, ZnO films were grown on the nucleation sides of freestanding diamond substrates with and without a ZnO homobuffer layer by the radio-frequency (RF) magnetron sputtering method. The effects of buffer layers on the properties of the ZnO film and UV photodetectors based on a ZnO/freestanding diamond film structure were studied. The experimental results suggested that the buffer layer was helpful in improving the crystalline quality of ZnO/diamond heteroepitaxial films and the electrical property of the ZnO photodetectors was relative to the crystalline quality of ZnO films. For the photodetector based on the ZnO film with a buffer layer, a higher value of photo-responsivity under a 10 V bias voltage and a better time-dependent photocurrent characteristic were obtained.

CVD diamond alpha-particle detectors with different electrode geometry.

In this paper, two types of detectors, one with a coplanar and the other with a sandwich geometry using an identical CVD diamond film, were fabricated in order to investigate the effects of the film microstructure on the performance of diamond film alpha-particle detectors. An average charge collection efficiency of 42.9% for the coplanar structure and of 37.4% for the sandwich structure detectors was obtained, respectively. Raman scattering studies directly demonstrated that the different counts, collection efficiencies and photocurrents of the two types of detectors mainly resulted from the different micro-structural features between the final growth side and the nucleation side of the diamond film. Under alpha particle irradiation the detector with sandwich geometry had a similar trend on energy resolution with coplanar geometry under different applied electric field. A good energy resolution of 1.1% was obtained for both detectors.

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.

Polymer photovoltaic cells by using manganese phthalocyanine derivative

A novel near-infrared absorbing manganese phthalocyanine bisphenol A epoxy derivative (MnPc-DGEBPA) was synthesized and characterized by infrared, UV–Vis and fluorescence spectra. The absorption spectrum of the derivative exhibited a Q-band in the near-infrared region and its fluorescence quantum yield reached 0.36 in N, N-dimethylformamide. MnPc-DGEBPA has high solubility and good film forming ability as well. The MnPc-DGEBPA films with a planar electrode were prepared by the dip-coating process using 2, 9, 16, 23-tetra-amino manganese phthalocyanine (TAMnPc) as a solidifying reagent. The current–voltage characteristics of the films were measured and photoconductivity was increased by an order of magnitude compared with dark conductivity, which indicates that MnPc-DGEBPA films have good photoelectric response. Schottky-type and pn-junction-type photovoltaic cells with ITO/MnPc-DGEBPA/Al and ITO/MnPc-DGEBPA/C60/Al structures were achieved by spin coating (using TAMnPc as a solidifying reagent) and vacuum evaporation. The open-circuit voltage (Voc) and short-circuit current density (Jsc) of the Schottky device were 0.6 V and 4.7 nA cm−2, while Voc and Jsc of the pn-junction device were 0.14 V and 0.45 µA cm−2, respectively. The photocurrent efficiency of the pn-junction cell was about 0.1%.

A nanocrystalline CVD diamond film as an x-ray radiation detector

In this work, an x-ray radiation detector was developed from a nanocrystalline diamond (NCD) film. The NCD film, with a grain size of about 20 nm and a thickness of ~5 µm, was deposited on a silicon substrate using a hot-filament chemical vapour deposition (HFCVD) method. The response to radiation and the energy resolution at room temperature of the obtained metal-NCD/Si-metal detector were investigated using 5.9 keV x-rays from a 55Fe source. With an electric field 50 kV cm−1, this detector showed a dark-current of ~5.88 µA, and under x-ray illumination a net response current of ~576 nA and an energy resolution of ~22.7%. It was also shown that the energy resolution deteriorated when the diamond grain size was reduced.

Preparation of free-standing diamond films for high frequency SAW devices

Abstract Free-standing diamond films were prepared by hot filament chemical vapor deposition (HFCVD) method under different conditions. Inter-digital transducers (IDTs) were formed on the nucleation sides of free-standing diamond films by photolithography technique. Then piezoelectric ZnO films were deposited by radio-frequency(RF) reactive magnetron sputtering to obtain the ZnO/diamond film structures. Surface morphologies of the nucleation sides and the IDTs were characterized by means of scanning electron microscopy (SEM), atomic force microscope (AFM) and optical microscopy. The results indicate that the surfaces of nucleation sides are very smooth and the IDTs are of high quality without discontinuity and short circuit phenomenon. Raman spectra show the sharp diamond feature peak at about 1 334 cm −1 and the small amount of non-diamond carbon in the nucleation side. X-ray diffraction (XRD) patterns of the structure of ZnO/diamond films show a strong diffraction peak of ZnO (002), which indicates that as-sputtered ZnO films are highly c -axis oriented.