Bo Qian

Oxygen induced strong green light emission from low-temperature grown amorphous silicon nitride films

Luminescent amorphous silicon nitride films were fabricated by plasma-enhanced chemical vapor deposition at room temperature followed by thermal oxidation at 100°C. Very bright green emissions were clearly observed with the naked eye in a bright room after the samples had been oxidized. The emission peak is located at 495nm. Fourier-transform infrared absorption spectra and results of depth profiling with x-ray photoelectron spectroscopy indicate that the introduction of oxygen is of a key role in enhancing the photoluminescence intensity of the films. Emission and excitation spectra analyses suggest that the green emission is originated from the radiative recombination in the localized states related to the Si–O bonds.

Excitation mapping of whispering gallery modes in silica microcavities

We report the direct observation of the electromagnetic-field distribution of whispering gallery modes in silica microcavities (spheres and toroids). It is revealed by their excitation efficiency with a tapered fiber coupler swept along the meridian. The originality of this method lies in the use of the coupler itself for the near-field mapping, eliminating the need of additional tools used in previous work. This method is successfully applied to microspheres and microtoroids.

High thermal stability and low density variation of carbon-doped Ge2Sb2Te5 for phase-change memory application

Carbon-doped Ge2Sb2Te5 (GSTC) film has been experimentally studied as a thermal stable material for high temperature applications. The 10-yr data retention temperature is remarkably increased through C doping. Furthermore, GSTC films have better interface properties after annealing at 410 °C for 30 min. The density variation of GSTC film is significantly improved, which is very important to device reliability. X-ray photoelectron spectroscopy results reveal that the thermal stability enhancement of GSTC film attributes to the forming of C-Ge, C-Sb, and C-Te bonds. The perfect thermal stability makes GSTC materials a good candidate in the actual production of phase-change memory.

Intermediate phase silicon structure induced enhancement of photoluminescence from thermal annealed a-Si/SiO2 multilayers

a-Si/SiO2 multilayers with different a-Si sublayer thicknesses were prepared by plasma enhanced chemical vapour deposition (PECVD). An intermediate phase silicon structure (IPSS), which is intermediate in order between the continuous random network amorphous phase and the well ordered crystalline phase, was discovered in the a-Si sublayers near the crystallization onset temperatures through Raman scattering and cross-section high resolution transmission electron microscopy (HRTEM). A strong broad photoluminescence (PL) band, consisting of two peaks centred at 773 nm and 863 nm respectively, was observed with the formation of the IPSS. Based on the analysis of the temperature dependence of PL, the strong PL emission bands centred at 863 and 773 nm are ascribed to the structural defects inside the IPSS and Si = O at the surface of the IPSS, respectively.

Size dependence of optical eigenmodes in photonic quantum dots prepared by conformal deposition method

An approach was proposed to achieve Si-based three-dimensional optical microcavities, in which photons were confined by Bragg reflectors in all dimensions instead of the lateral confinement by using total internal reflection. Size-dependent photonic energy modes were observed when the lateral size is changed from 4.5to1.5μm. With decreasing lateral size the modes shift to higher energies, and the splitting between the modes increases which indicates that the three-dimensional optical microcavity looks like photonic quantum dots. The observed discrete optical eigenmodes show a quantitative agreement with numerical calculations of quantized photon states in photonic quantum dots.

Faraday Effect sensor redressed by Nd 2 Fe 14 B biasing magnetic film

A Faraday Effect sensor with Nd(2)Fe(14)B biasing magnetic film was described. Ta/Nd(2)Fe(14)B/Ta films were grown by magnetron sputtering method. The magnetic domain in the sensor with the Nd(2)Fe(14)B biasing magnetic film can persist its distribution. The average linearity error of Faraday Effect sensor with biasing magnetic film decreased from 1.42% to 0.125% compared with non-biasing magnetic film, and the measurement range increased from 820 Oe to 900 Oe.

On-chip silicon-based active photonic molecules by complete photonic bandgap light confinement

We demonstrate an on-chip silicon-based active photonic molecule (PM) structures formed by two coupled photonic quantum dots with complete photonic bandgap (PBG) light confinement. The photonic quantum dots are grown by conformal deposition of amorphous silicon nitride multilayers on patterned substrates. A fine structure of the coupled optical modes in PMs has been observed which shows similarity to the electronic bonding (BN) and antibonding (ABN) states in a molecule.

Silicon based photonic quantum dots

We use a patterned conformal deposition technique to fabricate Si-based 3D optical microcavities. The size-dependent confined photonic modes were observed when the size is reduced to 1.0 mum which is similar to the quantum effect of electronic states in semiconductor quantum dots.

Optical magnetic field sensor improved by NdFeB ferromagnetic film

In this paper, two types of optical magnetic field sensors have been prepared, one was pure garnet magnetic field sensor, another was garnet with Ta/NdFeB/Ta film grown by magnetron sputtering method at the base pressure of 1.0×10-5Pa, and the working pressure was 0.8Pa. Ta film worked as buffer layer and protective layer, and the NdFeB worked as ferromagnetic film, the atom proportion of NdFeB was 2:14:1. The measuring was based on Magneto-optical Faraday effect. The Faraday rotation was obtained under the conditions of 1.55μm near-infrared light and the magnetic field in range of -150-150Oe. It was found that the garnet sensor with NdFeB film has lower linearity error 0.125% compared with pure garnet sensor 1.42%, and the difference was attributed to the presence of NdFeB ferromagnetic film interact on the garnet.

On-chip mode-control in active silicon-based photonic molecule by complete photon confinement

We have demonstrated an efficient way to build on-chip active silicon-based photonic molecules in complete photonic bandgap confinement [1]. Due to the conformal deposition processes on square patterns, the luminescent layers are naturally confined in three-dimensional photonic bandgap materials. The confined optical modes in photonic molecules exhibit very similar energy level structure as in chemical molecules. In this paper, the PMs with two different coupling distances were fabricated. The confined modes are precisely and conveniently controlled by such conformal method. We believe this convenient way will greatly promote the study of complex photonic molecule and the schemes of on-chip integrated photonic circuit structures.