Jianhua Ju

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.

Efficient luminescence from CVD diamond film-coated porous silicon

In this Letter a novel passivation method for porous silicon (PS) surfaces, i.e., depositing diamond film on a PS surface by microwave plasma assisted chemical vapour deposition (MPCVD) method, is reported. The morphologies, structure and PL of CVD diamond film coated PS were characterized using scanning electron microscopy (SEM), Raman spectrum and PL spectroscope. Results indicate that efficient luminescence can be obtained from diamond film-coated porous silicon. Also, the CVD diamond film may efficiently stabilize the PL wavelength and intensity of PS, and therefore is a promising candidate for passivation of porous silicon in the future.

Surfaces of undoped and boron doped polycrystalline diamond films influenced by negative DC bias voltage

Abstract The hydrogen ion bombardment is performed by applying a negative bias voltage to the substrate during microwave plasma chemical vapor deposition process, using only hydrogen as reactant gas. The size of (001) faces increases after hydrogen ion etching while other grains are etched off. The surfaces of [001]-oriented films after doping boron are investigated by scanning electron microscopy (SEM) and cathodoluminescent (CL) spectra. The absence of the band-A emission in the CL spectra means a low density of dislocation in the films. It is the first time that the peak at 741.5 nm and the broad peak at approximately 575 and 625 nm in the CL spectra were reduced efficiently after boron doping in (001) polycrystalline diamond films and to propose that these phenomena should be explained in simple terms with penetration of the lattice nets of the [001]-oriented faces model.

Electrical properties of chemical vapor deposition diamond films and electrical response to X-ray

Abstract In this paper, dark current–voltage (I–V) characteristics, current–temperature (I–T) characteristics, and photocurrents under steady-state X-ray excitation of CVD diamond films were investigated. Results indicated that dark currents and photocurrents by X-ray irradiation for the [001] textured CVD diamond film were greater than those for the non-textured one. The differences in dark currents and resistivities were attributed to a large number of grain boundaries contained in the non-textured diamond films. From the I–T curves, at the temperature higher than 500 K, currents clearly followed an exponential behavior because of the activation energy of E a =1.68 eV which was normally attributed to Si trapped to a vacancy in the diamond lattice.

Textured growth of [100] diamond on Al2O3 ceramic substrate by microwave plasma chemical vapor deposition

[100]-textured diamond thin film on a rough and randomly oriented Al2O3 substrate has been achieved by MPCVD. The cyclic technique--the cyclic modulation of the H2 plasma (etching process) and CH4+H2 plasma (growing process)--has been applied during the growth stage with various etching/growth time ratios. The dependencies of properties and morphologies of the films on the etching time interval were well explained by the selective etching of hydrogen ions to non-[100]- oriented grains. The strong effects of different methane concentrations and substrate temperatures on the [100]-textured growth were also concluded. Growth mechanisms of [100]-textured diamond thin films on Al2O3 substrates were discussed based on the detailed results of Scanning Electron Microscopy, Raman Spectrum and X-ray Diffraction Spectrum.

Microstructure and infrared optical properties of hydrogenated carbon nitride film

Microstructure and optical properties of nitrogen doped hydrogenated carbon (a-C:H:N) film deposited by rf plasma enhanced chemical vapor deposition method were studied by AFM, Raman, FTIR and IRE spectrometer. 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 ratio of flux N2/CH4. Raman spectra show the shape of D and G band of a-C:H:N film varies slightly with the increase of N content, which means the main structures of N doped films are still diamondlike carbon films. However Gaussian fit results show that G band widens and the peak shifts to the low wavenumber in Raman spectra is that amorphous C3N4 structure formed in the film. AFM topographies and LFM images of a-C:H:N film confirm the amorphous C3N4 exists as several ten nanometers particles in the film. IRE spectra analysis results show that refractive index of the film in infrared band (2 - 14 um) slightly decreases from 1.8 to 1.6 with increased nitrogen content in the films.

Defects eliminated by hydrogen and boron ion bombardment in polycrystalline diamond films

Bombardments of hydrogen and boron ions are performed by applying a negative bias voltage to the substrate during microwave plasma chemical vapor deposition process. The size of (001) faces increases after hydrogen ion etching, while other grains are etched off. The surfaces of [001]- oriented films after boron dying are investigated by scanning electron microscope and cathodoluminescent (CL) spectra. The absence of the band-A emission in the CL spectra means a low density of dislocations in the films. It is the first time to indicate that the peak at 741.5 nm and the broad peak at around 575 and 625 nm in the CL spectra are reduced efficiently after boron doping in (001) polycrystalline diamond films. We propose that these phenomena could be explained in simple terms by a penetration or adsorption model through the lattice nets of the [001]-oriented surfaces.