Zhifeng Li

Microstructures and optical properties in crystallized a-Si:H multi-quantum wells using excimer laser annealing

Abstract The visible light emission from KrF excimer laser crystallized a-Si:H/a-SiNx:H multi-quantum well (MQW) films at room temperature is reported. Both X-ray diffraction (XRD) and Raman scattering spectra provide evidence for the crystallization of Si layers within the MQWs after laser annealing treatment. Transmission electron micrographs (TEM) show the perfect conservation of the layered structures and proves the mechanism of constrained crystallization by stable a-SiNx:H barrier layers during laser annealing. The peak wavelength of visible PL spectra of the crystallized samples is around 640 nm (∼ 1.94 eV) and does not shift with different exposure energy. The FWHM of the PL peak becomes narrower to 0.4 eV when the irradiation energy density is increased to 0.9 J/cm2.

Novel photoluminescence from hydrogenated amorphous carbon films prepared by using xylene source

Hydrogenated amorphous carbon thin films were prepared by using organic hydrocarbon source, xylene (C 8 H 10 ), in a plasma enhanced chemical vapor deposition-(PECVD) system. In contrast to a single broad PL peak from methane (CH 4 )-based hydrogenated amorphous carbon films, a new PL feature was observed from xylene-based a–C:H films in the blue-green light region. It was found that the aromatic-structures were enhanced in xylene-based a–C:H films deposited at high radio frequency power, which may result in the existence of luminescence centers in the carbon films and induce the appearance of a new PL peak.

Ar+ laser crystallization of a-Si:H film for active layer of TFT

Abstract The high quality crystallized films of a-Si:H have successfully been obtained by the Ar+ laser scanning irradiation. The analyses of cross-section TEM show that a liquid phase laser crystallization region (LP-LCR) has the chevron grain structure with average grain size of about 40 μm under the conditions of powers (3.0–3.5 W) and speeds (3–5 cm/s). The results of X-ray, Raman Spectra and SIMS indicate that preferential crystal orientation is in the direction of and crystallized films still contain about 2 × 1020 H atoms cm−3 Dark conductivity of the crystallized film is about five orders of magnitude larger than that of as-deposited a-SI:H film at room temperature.

Radiative transition with visible light in crystallized aGe:H/aSiNX:H multiquantum-well structures

Abstract Crystallized aGe:H/aSiNX: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.

The study of optical nonlinearity in amorphous Si-based alloys

Amorphous all-dielectric Fabry-Perot interference filters were adopted as a prototype for studying optical bistability. Room-temperature optical bistability has been demonstrated in hydrogenated amorphous silicon-carbon alloys at wavenlength about 532 nm. The switching intensity which should be required <0.5 W/μm 2

Structure and Photoluminescence of Hydrogenated Amorphous Carbon Films Produced by Using Aromatic Hydrocarbon Source

The organic carbon source –xylene(C 6 H 6 -C 2 H 4 ), was used to fabricate a-C:H films in plasma enhanced chemical vapor deposition system. The structures and bonding configurations were characterized and compared with that of conventional methane-based samples by using Fourier Transform Infrared spectroscopy and Raman scattering technique. Strong room temperature luminescence in blue-green light range was found and the PL feature was quite different from that of methane-based a-C:H films.

Visible photo- and electro-luminescence from laser-crystallized a-Si:H and its based multilayers

We have reported for the first time on visible photoluminescence (PL) in crystallized a-Si:H/aSiNx:H multilayers structure by CW Ar ion laser annealing treatments. In this paper we present new results on visible PL and electroluminescence (EL) from crystallized a:SiH and its based multilayers by using KrF excimer pulse laser irradiating treatments. Strong and stable PL and EL have been observed by naked eye in both laser irradiated a-Si:H and a-Si:H/aSiNx:H multilayers samples at room temperature. The EL peak of crystallized a-Si:H/a-SiNx:H multilayers is blue shifted from 1.79 eV to 2.00 eV with narrowing the well layer thickness from 4 nm to 2 nm which suggests the origin of the light emission should be related to the quantum size effect.

Microstructures and visible photoluminescence of excimer laser crystallized a-Si:H/a-SiN/sub x/:H multi-quantum wells

We report the visible photoluminescence (PL) at room temperature from KrF excimer laser annealed a-Si:H/a-SiN/sub x/:H multi-quantum wells (MQWs). X-ray diffraction (XRD) and Raman scattering spectra demonstrate the microstructures of crystallized silicon within the MQWs and the crystallinity which can be controlled by excimer laser energy density. The wavelength of PL peak is around 640 nm and does not shift significantly with excimer laser energy.

KrF laser-induced nanometer Si crystallites formation and TEM observation

The authors report the preparation of the nanometer Si crystallites constrained between a-SiN{sub x}:H barrier layers by means of KrF excimer laser induced crystallization. X-ray diffraction (XRD) and Raman scattering spectra demonstrate that ultra thin a-Si:H well layers have been crystallized. The average grain size of Si crystallites is on the order of magnitude of a nanometer. Small-angle XRD spectrum indicates multilayer structures have not undergone laser damage. The results of TEM are presented to show smooth and abrupt interfaces of layered structures and nanometer Si crystallites arrayed one-by-one in the Si layer. The thermodynamics of KrF laser-induced crystallization of ultra-thin Si layer has been discussed.

Luminescent Si quantum dots films: preparation and characterization

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.