Hydrogenated amorphous silicon carbon alloys (a-SiCx:H) were fabricated by radio frequency glow discharge technique. The optically bistable phenomenon was observed for the first time using those uncoated materials as nonlinear medium. The effect was obtained with a high intensity Nd:YAG laser at the room temperature. The excitation wavelength is 532 nm and the switching time is in the nanosecond scale. The different two kinds of nonlinear characteristics have been observed, which can be tentatively explained using the band-tail states blocking effect and thermal effect respectively. © 1993.

Chen Kunji;Xu Jun;Huang Xinfan;Feng Duan;Zhuang Dakui;Li Qun;Wang Wenyao;Qiu Peihua

Solid State Communications

1993

Crystallized aGe:H/aSiNX:H multiquantum-well (MQW) structures were prepared by a computer controlled plasma enhanced chemical vapor deposition method and then crystallized by Ar⁺ laser annealing technique. The layered structures and the crystallinity of the samples were determined by means of X-ray diffraction (XRD) spectroscopy. The crystallized samples showed a radiative transition with visible light as the Ge well layer thickness was less than 4 nm. This may preliminary be explained by the quantum confinement of electrons and holes. © 1993.

Chen K. J.;Jiang J. G.;Huang X. F.;Li Z. F.;Qu X. X.;Du J. F.;Feng D.

Journal of Non Crystalline Solids

1993

Preparation of Ge quantum crystallites embedded in a-SiNx matrix was successfully achieved by the PECVD technique and followed thermal annealing treatment at 800°C. The microscopic heterogeneity of the as-deposited and thermal-annealed films were analyzed by the TEM and X-ray diffraction. We have found that substrate temperature is a critical parameter for the formation of Ge clusters. The temperature and time duration of annealing determine the size of Ge quantum crystallites. We are temporarily using the diffusion-limited growth model to explain the crystallization mechanism of this quantum material. © 1994.

Qu X. X.;Chen K. J.;Wang M. X.;Li Z. F.;Shi W. H.;Feng D.

Solid State Communications

1994

Photoinduced light scattering of LiTaO 3 :Nd crystal (0.1 wt %) was examined by using a focused He-Ne laser beam. When an ordinary incident beam illuminates the sample along the y axis, the scattered light is asymmetrical in the xy plane, and the scattered intensities display a time-dependent distribution with a gradual increase and decrease for the ordinary and extraordinary beams, respectively. The situation is reversed for an extraordinary incident beam. When an incident beam with ordinary or extraordinary polarizations illuminates the sample along the x axis, two scattered specklons are dependent upon the crossing angle with almost the same intensity. We attribute them to a new photorefractive effect due to the microstructure change in LiTaO 3 crystal with Nd doping. In addition, Raman spectra concerning the observed scattered structures are also measured and elucidated.

Wu Xinglong;Zhang Ming-Sheng;Chen Xiaoyuan;Meng Xiangkang;Feng Duan

Applied Physics Letters

1994

Ge nanocrystals embedded in a-SiNx matrix were prepared by the PECVD method with SiH4, GeH4 and NH3 mixed in H2 plasma and followed the thermal-annealing treatment, which was based on the preferential chemical bonding formation of Si-N and Ge-Ge. The samples were characterized by infrared absorption, X-ray diffraction, Raman scattering spectra and TEM micrograph. Visible photoluminescence was observed at room temperature with the PL peak at about 560 nm and the linewidth about 0.45 eV. We are temporarily using the quantum confinement model to explain the PL mechanism.

Qu Xuexuan;Huang Xinfan;Chen Kunji;Li Zhifeng;Feng Duan

Proceedings of SPIE the International Society for Optical Engineering

1994

The waveguiding epitaxial LiTaO 3 and LiNbO 3 films have been prepared on sapphire substrates by pulsed laser deposition technique. The as-grown films were characterized by Raman scattering, XRD and SEM techniques, which revealed that epitaxial LiTaO 3 and LiNbO 3 films with small roughness were achieved on (001) and (012) sapphire substrates, respectively. Optical waveguiding properties were demonstrated by m-line measurement of TM and TE modes.

Liu Junming;Liu Zhiguo;Zhu Shining;Wu Zhuangchun;Zhang Ming Sheng;Feng Duan

Proceedings of SPIE the International Society for Optical Engineering

1994

We report two kinds of method for preparing luminescent silicon films with quantum crystallites (QCs) structures: (1) Using laser annealing technique to crystallize ultrathin amorphous silicon layers which were constructed in a-Si:H/a-SiNx:H multiquantum well (MQW) structures. (2) Applying the layer-by-layer deposition technique to the growth of silicon QCs by varying the hydrogen plasma exposure time. The novel structures of these two types of QCs films were characterized by X-ray diffraction and Raman scattering spectroscopy. The room temperature visible photoluminescence (PL) from Si QCs with size of 4 nm or less has been observed in most of samples.

Chen Kunji;Huang Xinfan;Chen Maorui;Shi Weihua;Li Zhifeng;Feng Duan

Proceedings of SPIE the International Society for Optical Engineering

1994

Raman spectra of LiNbO3 and LiTaO3 crystals with different proton-exchanged time were examined. Two new vibrational modes at 38 and 58cm^-1 were found. The 38cm^-1 mode shows a line spectrum and its intensity changes with proton-exchanged time. The 58cm^-1 mode, which exists only in the Raman spectrum of protonated LiNbO3 crystal with 14 hours treatment, shows a large intensity and a broad line. We attribute the 38 and 58cm^-1 modes to a localized vibrational mode resulted from defect-induced disorder and a second-order Raman scattering mode, respectively. The properties of the two modes really reflect the microstructure change of the protonated samples. © 1994.

Wu Xing-long;Zhang Ming-sheng;Yan Feng;Feng Duan

Solid State Communications

1995

We report a new method for synthesizing Ge nano-crystallites embedded in SiNy film matrices. On the basis of the effect of the reactant precursors and preferential chemical bonding of Si-N and Ge-Ge, thin films with Ge clusters embedded in SiNy matrices have been prepared in the PECVD system with reactant gases of SiH4, GeH4 and NH3 mixed in the hydrogen plasma. The as-deposited films were then crystallized by Ar ion laser annealing or thermal annealing technique to form nanometer-sized Ge crystallites. The composition and microstructures of these new type of sample were characterized by infrared absorption spectra, transmission electron microscopy, X-ray diffraction and Raman scattering spectra. The results indicated that the average size of Ge crystallites was estimated to be 2-20 nm depending on the deposition and annealing parameters and can be controlled by a designed manner.

Chen Kunji;Qu Xuexuan;Huang Xinfan;Li Zhifeng;Feng Duan

Materials Research Society Symposium Proceedings

1995

The constrained crystallization in a-Si:H/a-SiNx:H multilayer structures by Ar ion laser annealing treatment has been studied by high-resolution transmission electron microscopy (HRTEM) and Raman scattering. HRTEM photograph shows that the a-Si:H layers crystallize without disturbing the multilayer structures and that the interfaces after the crystallization are atomically smooth and uniform. The lattice image of the Si crystallites arrayed one by one can be seen clearly in Si layers and the average size is roughly equal to the thickness of Si layer. The thermodynamics of constrained crystallization within multilayer structures has been discussed.

Huang Xinfan;Shi Weihua;Chen Kunji;Yu Shidong;Feng Duan

Materials Research Society Symposium Proceedings

1995