San Chen

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.

Photocurrent in Ag–Si photodiodes modulated by plasmonic nanopatterns

We demonstrate that Ag–Si photodiodes allow photocurrents to be modulated by changing periods of nanopatterns on Ag film. The maximum and minimum photocurrents occur in certain periods corresponding to the excitation of surface plasmon polariton and Wood’s anomaly, which can be predicted with the help of related theories. Therefore, it is feasible to design nanopatterns to satisfy special requirements.

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.

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.

Comparison of superconducting properties between FeSe0.5Te0.5/CeO2/SrTiO3 and FeSe0.5Te0.5/SrTiO3 thin films

The electrical resistance behaviors under angle-dependent magnetic fields up to 16 T are investigated in superconducting FeSe0.5Te0.5 (FST) thin films grown on SrTiO3 (STO) substrates without or with a CeO2 buffer layer. It is found that the FST/CeO2/STO films have an enhanced superconducting transition temperature Tc and slightly increased superconducting anisotropy in comparison with the FST/STO films. The enhancement of Tc in the presence of the CeO2 buffer is closely related to the changes in both the out-of-plane lattice constant and Se-Fe-Se (Te-Fe-Te) bond angle.

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.

Silicon-based one-dimensional photonic crystal microcavity

The layer-by-layer method is employed to prepare a-SiNx:H microcavity structure in a Plasma Enhanced Chemical Vapor Deposition (PECVD) chamber. Measurements of transmittance spectrum of as-grown samples show that the transmittance resonant peak of a cavity mode at 750 nm is introduced into the band gap of one-dimensional photonic crystal distributed Bragg reflectors based on hydrogenated amorphous silicon nitride. Also the PL measurements of a-SiNx:H microcavities are performed. There is a well agreement between the transmittance spectra and the PL of microcavity samples. In order to clarify the microcavity effects on the bulk a-SiNx:H, the PL of a λ/2-thick layer of bulk a-SiNx:H obtained under the same experimental conditions is presented. By comparison, a dramatic narrowing of emission linewidth and enhancement of PL intensity is observed. The wide emission band with 208 nm is strongly narrowed to 17 nm, and the resonant enhancement of the peak PL intensity is about two orders of magnitude with respect to the emission of the λ/2-thick layer of bulk a-SiNx:H. A linewidth of Δλ=17 nm and a quality factor of Q=50 are achieved in our one-dimensional a-SiNx photonic crystal microcavities.