Effects of annealing on the color, absorption spectra, and light yield of Ce : YAlO3 single crystal grown by the temperature gradient technique

YAlO3 single crystal doped with Ce3+ at concentration 1% was grown by the temperature gradient technique. The as-grown crystal was pink. After H-2 annealing or air annealing at 1400degreesC for 20 h, the crystal was turned into colorless. We concluded there were two kinds of color centers in the as-grown crystal. One is F+ center attributed to absorption band peaking at about 530 nm, the other is O- center attributed to absorption band peaking at about 390 nm. This color centers model can be applied in explaining the experiment phenomena including the color changes, the absorption spectra changes, and the light yield changes of Ce:YAP crystals before and after annealing. (C) 2004 American Institute of Physics.

Effect of air annealing on the spectral properties of Ce : Y3Al5O12 single crystals grown by the temperature gradient technique

Five absorption hands, at 227, 300 340, 370 and 457nm, were observed in the optical absorption spectrum of Ce:Y3Al5O12 (Ce:YAG) crystals grown by the temperature gradient technique (TGT). The absorption bands at 227, 340, and 457 nm were identified Lis belonging to the Ce3+ -ion in the YAG crystal. A near UV optical emission band at 398nm was observed. with an excitation spectrum containing two bands, at 235 and 370nm. No fluorescence was detected under 300 nm excitation. The pair of absorption bands at 235 and 370 nm and the absorption band at 300 nm were attributed to the F- and F+-type color centers, respectively. The color centers model was also applied to explain the spectral changes in the Ce:YAG (TGT) crystal, including the reduction in the Ce 31 -ion absorption intensity, after annealing in an oxidizing atmosphere (air). (C) 2004 Elsevier B.V. All rights reserved.

Crystallization of amorphous Si films by pulsed laser annealing and their structural characteristics

Nanocrystalline silicon (nc-Si) films were prepared by pulsed laser annealed crystallization of amorphous silicon (alpha-Si) films on SiO2-coated quartz or glass substrates. The effect of laser energy density on structural characteristics of nc-Si films was investigated. The Ni-induced crystallization of the a-Si films was also discussed. The surface morphology and microstructure of these films were characterized by scanning electron microscopy, high-resolution electron microscopy, atomic force microscopy and Raman scattering spectroscopy. The results show that not only can the alpha-Si films be crystallized by the laser annealing technique, but also the size of Si nanocrystallites can be controlled by varying the laser energy density. Their average size is about 4-6 nm. We present a surface tension and interface strain model used for describing the laser annealed crystallization of the alpha-Si films. The doping of Ni atoms may effectively reduce the threshold value of laser energy density to crystallize the alpha-Si films, and the flocculent-like Si nanostructures could be formed by Ni-induced crystallization of the alpha-Si films.

Improved surface morphology of stacked 1.3 mu m InAs/GaAs quantum dot active regions by introducing annealing processes

The authors report a simple but effective way to improve the surface morphology of stacked 1.3 mu m InAs/GaAs quantum dot (QD) active regions grown by metal-organic chemical vapor deposition (MOCVD), in which GaAs middle spacer and top separate confining heterostructure (SCH) layers are deposited at a low temperature of 560 degrees C to suppress postgrowth annealing effect that can blueshift emission wavelength of QDs. By introducing annealing processes just after depositing the GaAs spacer layers, the authors demonstrate that the surface morphology of the top GaAs SCH layer can be dramatically improved. For a model structure of five-layer QDs, the surface roughness with the introduced annealing processes (IAPs) is reduced to about 1.3 nm (5x5 mu m(2) area), much less than 4.2 nm without the IAPs. Furthermore, photoluminescence measurements show that inserting the annealing steps does not induce any changes in emission wavelength. This dramatic improvement in surface morphology results from the improved GaAs spacer surfaces due to the IAPs. The technique reported here has important implications for realizing stacked 1.3 mu m InAs/GaAs QD lasers based on MOCVD.

The evolution of InAs/InAlAs/InGaAlAs quantum dots after rapid thermal annealing

We have studied how the optical properties of InAs self-assembled quantum dots (QDs) grown on GaAs substrate are affected when depositing an InAlAs/InGaAs combination overgrowth layer directly on it by rapid thermal annealing (RTA). The photoluminescence measurement demonstrated that the InAs QDs experiences an abnormal variation during the course of RTA. The model of transformation of InAs-InAlAs-InGaAlAs could be used to well explain the phenomena. (C) 2003 Elsevier Science B.V. All rights reserved.

The microstructure and its high-temperature annealing behaviours of a-Si : O : H film

The microstructure and its annealing behaviours of a-Si:O:H film prepared by PECVD are investigated in detail using micro-Raman spectroscopy, X-ray photoelectron spectroscopy and Infrared absorption spectroscopy. The results indicate that the as-deposited a-Si:O:H film is structural inhomogeneous, with Si-riched phases surrounded by O-riched phases. The Si-riched phases are found to be nonhydrogenated amorphous silicon (a-Si) clusters, and the O-riched phases SiOx:H (x approximate to 1. 35) are formed by random bonding of Si, O and H atoms. By high-temperature annealing at 1150 degreesC, the SiOx:H (x approximate to 1.35) matrix is shown to be transformed into SiO2 and SiOx ( x approximate to 0.64), during which all of the hydrogen atoms in the film escape and some of silicon atoms are separated from the SiOx:H ( x approximate to 1.35) matrix; The separated silicon atoms are found to be participated in the nucleation and growth processes of solid-phase crystallization of the a-Si clusters, nano-crystalline silicon (ne-Si) is then formed. The microstructure of the annealed film is thereby described with a multi-shell model, in which the ne-Si clusters are embedded in SiOx (x = 0.64) and SiO2. The former is located at the boundaries of the nc-Si clusters, with a thickness comparable with the scale of nc-Si clusters, and forms the transition oxide layer between the ne-Si and the SiO2 matrix.

Thermodynamic model of hydrogen-induced silicon surface layer cleavage

A thermodynamic model of hydrogen-induced silicon surface layer splitting with the help of a bonded silicon wafer is proposed in this article. Wafer splitting is the result of lateral growth of hydrogen blisters in the entire hydrogen-implanted region during annealing. The blister growth rate depends on the effective activation energies of both hydrogen complex dissociation and hydrogen diffusion. The hydrogen blister radius was studied as a function of annealing time, annealing temperature, and implantation dose. The critical radius was obtained according to the Griffith energy condition. The time required for wafer splitting at the cut temperature was calculated in accordance with the growth of hydrogen blisters. (C) 2001 American Institute of Physics.

Light and annealing induced changes in Si-H bonds in undoped a-Si : H

Light and annealing induced changes in Si-H bonds in undoped a-Si:H have been investigated by a differential infrared spectroscopy method. The light-induced changes in Si-H bonds are not monotonic, quite different from the usual Staebler-Wronski effect in electronic properties, and involve more complicated physics. The magnitude of the light-induced changes in Si-H bonds is proportional to the hydrogen content in the film. There may exist more than one microscopic process which determine the light-induced changes in Si-H bonds. Almost the whole a-Si:H network is affected when a-Si:H is subjected to Light-soaking or to annealing. The light-induced changes in Si-H bonds may be an independent light-induced phenomenon or an auxiliary process of the metastable SWE defect creation. (C) 2000 Elsevier Science Ltd. All rights reserved.

Modeling the dynamics of Si wafer bonding during annealing

The bonding behavior of silicon wafers depends on activation energy for the formation of siloxane bonds. In this article we developed a quantitative model on the dynamics of silicon wafer bonding during annealing. Based on this model, a significant difference in the bonding behaviors is compared quantitatively between the native oxide bonding interface and the thermal oxide bonding interface. The results indicate that the bonding strength of the native oxide interface increases with temperature much more rapidly than that of the thermal oxide interface. (C) 2000 American Institute of Physics. [S0021-8979(00)05520-1].

Arsenic clusters on the surface of vertically aligned InAs islands on GaAs substrate by annealing

The formation of arsenic clusters in a system of vertically aligned InAs quantum islands on GaAs during thermal annealing under As overpressure has been investigated by transmission electron microscopy (TEM) and Raman scattering. Semicoherent arsenic clusters, identified by TEM examination, have been formed on the surface of the GaAs capping layer. The existence of arsenic precipitates is also confirmed by Raman spectra, showing new peaks from the annealed specimen at 256 and 199 cm(-1). These peaks have been ascribed to A(1g) and E-g Raman active phonons of crystalline arsenic. The phenomenon can be understood by a model of strain-induced selected growth under As overpressure. (C) 1999 American Institute of Physics. [S0003-6951(99)02045-8].

Photoluminescence and activation on SI-GaAs by Si+ implantation and following rapid thermal annealing

Photoluminescence (PL) and electrical characteristics of SI-GaAs, Si+-implanted and following rapid thermal annealing (RTA), were investigated, The PL spectra of Si-GA-C-As, Ga-i-Si-As, and V-As-Si-As were obtained. This paper concentrates on the PL peak at 1.36 eV which was proven as an emission of the Si-Ga-V-Ga combination by Si+ + P+ dual implantation. The results indicate that the peak at 1.36 eV appears when the ratio of As:Ga increased during the processing. Also high activation was obtained for the sample under the same conditions. More discussion on the mechanism of Si+ implanted SI-GaAs has been made based on the Morrow model [J. Appl. Phys, 64 (1988) 1889].

Thermodynamic model of helium and hydrogen co-implanted silicon surface layer splitting

A thermodynamic model of the evolution of microcracks in silicon caused by helium and hydrogen co-implantation during annealing was studied. The crack growth rate relies on the amount of helium atoms and hydrogen molecules present. Here, the crack radius was studied as a function of annealing time and temperature, and compared with experimental results. The mean crack radius was found to be proportional to the annealing temperature and the helium and hydrogen implanted fluence. The gas desorption should be considered during annealing process. (C) 2009 Elsevier B.V. All rights reserved.

Influence of annealing on structure of Nylon 11

Differential scanning calorimeter (DSC), wide-angle X-ray diffraction (WAXD), small-angle X-ray scattering (SAXS), and density techniques have been used to investigate the structural parameters of the solid state of Nylon 11 annealed at different temperatures. The equilibrium heat of fusion Delta H-m(0) and equilibrium melting temperature T-m(0) were estimated to be 189.05 J g(-1) and 202.85 degrees C respectively by using the Hoffman-Weeks approach. The degree of crystallinity (W-c,W-x) ranged approximately 24-42% was calculated by WAXD and compared with those by calorimetry (W-c,W-h) and density (W-c,W-d) measurements. The radius of gyration R-g, crystalline thickness L-c, noncrystalline thickness L-a, long period L, semiaxes of the particles (a, b), electron-density difference between the crystalline and noncrystalline regions eta(c) - eta(a), and the invariant Q increased with increasing annealing temperature. The analysis of the SAXS data was based upon the particle characteristic function and the one-dimensional electron-density correlation function. An interphase region existed between the crystalline and noncrystalline region with a clear dimension of about 2 nm for semicrystalline Nylon 11. Instead of the traditional two-phase model, a three-phase model has been proposed to explain these results by means of SAXS.