Influence of substrate temperature on properties of MgF2 coatings

Thermal boat evaporation was employed to prepare MgF2 single-layer coatings upon both JGS1 and UBK7 substrates at different substrate temperatures. Microstructure, transmittance and residual stress of these coatings were measured by X-ray diffraction, spectrophotometer, and optical interferometer, respectively. Measurement of laser induced damage threshold (LIDT) of the samples was performed at 355 nm, 8 ns pulses. The results showed that high substrate temperature was beneficial to crystallization of the film. Above 244 degrees C, the refractive index increased gradually with the substrate temperature rising. Whereas, it was exceptional at 210 degrees C that the refractive index was higher than those deposited at 244 and 277 degrees C. The tensile residual stresses were exhibited in all MgF2 films, but not well correlated with the substrate temperature. In addition, the stresses were comparatively smaller upon JGS1 substrates. A tendency could be seen that the LIDTs reached the highest values at about 244 degrees C, and the films upon JGS1 had higher LIDTs than those upon UBK7 substrates at the same temperature. Meanwhile, the damage morphologies showed that the laser damage of the coating resulted from an absorbing center at the film-substrate interface. The features of the damages were displayed by an absorbing center dominated model. Furthermore, the reason of the difference in LIDT values was discussed in detail. (C) 2007 Elsevier B.V. All rights reserved.

Characterization of LaF3 coatings prepared at different temperatures and rates

LaF3 thin films were prepared by thermal boat evaporation at different substrate temperatures and various deposition rates. X-ray diffraction (XRD), Lambda 900 spectrophotometer and X-ray photoelectron spectroscopy (XPS) were employed to study crystal structure, transmittance and chemical composition of the coatings, respectively. Laser-induce damage threshold (LIDT) was determined by a tripled Nd:YAG laser system with a pulse width of 8 ns. It is found that the crystal structure became more perfect and the refractive index increased gradually with the temperature rising. The LIDT was comparatively high at high temperature. In the other hand, the crystallization status also became better and the refractive index increased when the deposition rate enhanced at a low level. If the rate was super rapid, the crystallization worsened instead and the refractive index would lessen greatly. On the whole, the LIDT decreased with increasing rate. (C) 2007 Elsevier B.V. All rights reserved.

The growth temperatures dependence of optical and electrical properties of InN films

InN films grown on sapphire at different substrate temperatures from 550 degrees C to 700 degrees C by metalorganic chemical vapor deposition were investigated. The low-temperature GaN nucleation layer with high-temperature annealing (1100 degrees C) was used as a buffer for main InN layer growth. X-ray diffraction and Raman scattering measurements reveal that the quality of InN films can be improved by increasing the growth temperature to 600 degrees C. Further high substrate temperatures may promote the thermal decomposition of InN films and result in poor crystallinity and surface morphology. The photoluminescence and Hall measurements were employed to characterize the optical and electrical properties of InN films, which also indicates strong growth temperature dependence. The InN films grown at temperature of 600 degrees C show not only a high mobility with low carrier concentration, but also a strong infrared emission band located around 0.7 eV. For a 600 nm thick InN film grown at 600 degrees C, the Hall mobility achieves up to 938 cm(2)/Vs with electron concentration of 3.9 x 10(18) cm(-3).

The effects of substrate temperature on the structure and properties of ZnO films prepared by pulsed laser deposition

ZnO thin films were prepared by pulsed laser deposition (PLD) on glass substrates with growth temperature from room temperature (RT) to 500 degrees C. The effects of substrate temperature on the structural and optical properties of ZnO films have been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission spectra, and RT photoluminescence (PL) measurements. The results showed that crystalline and (0 0 2)-oriented ZnO films were obtained at all substrate temperatures. As the substrate temperature increased from RT to 500 degrees C, the ratio of grain size in height direction to that in the lateral direction gradually decreased. The same grain size in two directions was obtained at 200 degrees C, and the size was smallest in all samples, which may result in maximum E, and E-0 of the films. UV emission was observed only in the films grown at 200 degrees C, which is probably because the stoichiometry of ZnO films was improved at a suitable substrate temperature. It was suggested that the UV emission might be related to the stoichiometry in the ZnO film rather than the grain size of the thin film. (c) 2007 Elsevier Ltd. All rights reserved.

Properties of high k gate dielectric gadolinium oxide deposited on Si(100) by dual ion beam deposition (DIBD)

Gadolinium oxide thin films have been prepared on silicon (100) substrates with a low-energy dual ion-beam epitaxial technique. Substrate temperature was an important factor to affect the crystal structures and textures in an ion energy range of 100-500 eV. The films had a monoclinic Gd2O3 structure with preferred orientation ((4) over bar 02) at low substrate temperatures. When the substrate temperature was increased, the orientation turned to (202), and finally, the cubic structure appeared at the substrate temperature of 700 degreesC, which disagreed with the previous report because of the ion energy. The AES studies found that Gadolinium oxide shared Gd2O3 structures, although there were a lot of oxygen deficiencies in the films, and the XPS results confirmed this. AFM was also used to investigate the surface images of the samples. Finally, the electrical properties were presented. (C) 2004 Elsevier B.V. All rights reserved.

脉冲激光晶化非晶硅薄膜的有限差分模拟

根据热传导原理，建立了脉冲激光晶化非晶硅薄膜的理论模型。运用有限差分方法研究了不同激光波长、能量密度等因素对薄膜温度变化及相变过程的影响。计算了不同波长激光器对厚度500nm非晶硅晶化的阈值能量密度。结果发现，准分子晶化的阈值能量密度最低，但是在同样的能量密度下，熔融深度却不及使用更长波长的激光器。计算并分析了升高衬底温度对结晶速度和晶粒尺寸的影响，模拟结果较好地验证了实验结论和规律。

MOCVD growth and properties of ZnO thin films on LiNbO3 substrates

ZnO thin films were grown on (0001)LiNbO3 substrates by the MOCVD technique. The substrate temperatures during growth were changed from 400 to 600 degrees C. The X-ray diffraction (XRD) pattern of the ZnO film showed a strong [002] reflection peak, and the peak intensity was dependent on substrate temperature. The ZnO columnar grains were highly oriented along the (002) direction when the film processing temperature was 600 degrees C. The optical transmission and PL results also indicated that highest crystalline quality of the ZnO films could be obtained at elevated temperatures. (c) 2005 Elsevier B.V. All rights reserved.

Effects of crystalline quality on the ultraviolet emission and electrical properties of the ZnO films deposited by magnetron sputtering

The ZnO films were deposited on c-plane sapphire, Si (0 0 1) and MgAl2O4 (1 1 1) substrates in pure Ar ambient at different substrate temperatures ranging from 400 to 750 degrees C by radio frequency magnetron sputtering. X-ray diffraction, photoluminescence and Hall measurements were used to evaluate the growth temperature and the substrate effects on the properties of ZnO films. The results show that the crystalline quality of the ZnO films improves with increasing the temperature up to 600 degrees C, the crystallinity of the films is degraded as the growth temperature increasing further, and the ZnO film with the best crystalline quality is obtained on sapphire at 600 degrees C. The intensity of the photoluminescence and the electrical properties strongly depend on the crystalline quality of the ZnO films. The ZnO films with the better crystallinity have the stronger ultraviolet emission, the higher mobility and the lower residual carrier concentration. The effects of crystallinity on light emission and electrical properties, and the possible origin of the n-type conductivity of the undoped ZnO films are also discussed. (C) 2009 Elsevier B. V. All rights reserved.

Properties of high k gate dielectric gadolinium oxide deposited on Si(100) by dual ion beam deposition (DIBD)

Gadolinium oxide thin films have been prepared on silicon (100) substrates with a low-energy dual ion-beam epitaxial technique. Substrate temperature was an important factor to affect the crystal structures and textures in an ion energy range of 100-500 eV. The films had a monoclinic Gd2O3 structure with preferred orientation ((4) over bar 02) at low substrate temperatures. When the substrate temperature was increased, the orientation turned to (202), and finally, the cubic structure appeared at the substrate temperature of 700 degreesC, which disagreed with the previous report because of the ion energy. The AES studies found that Gadolinium oxide shared Gd2O3 structures, although there were a lot of oxygen deficiencies in the films, and the XPS results confirmed this. AFM was also used to investigate the surface images of the samples. Finally, the electrical properties were presented. (C) 2004 Elsevier B.V. All rights reserved.

The fabrication of self-aligned InAs nanostructures on GaAs(331)A substrates

Self-aligned InAs quantum wires (QWRs) or three-dimensional (3D) islands are fabricated on GaAs(331)A substrates by molecular beam epitaxy (MBE). InAs QWRs are selectively grown on the step edges formed by GaAs layers. The surface morphology of InAs nanostructures is carefully investigated by atomic force microscopy (AFM) measurements. Different growth conditions, such as substrate temperature, growth approaches, and InAs coverage, exert a great effect on the morphology of InAs islands. Low substrate temperatures favour the formation of wirelike nanostructures, while high substrate temperatures favour 3D islands. The shape transition is attributed to the trade-off between surface energy and strain energy. A qualitative agreement of our experimental data with the theoretical results derived from the model proposed by Tersoff and Tromp is achieved.

The correlation between preferred orientation and performance of ITO thin films

The tin-doped indium oxide (ITO) thin films were prepared by reactive thermal evaporation on the glass substrates. The effects of substrate temperatures (T-s) on the grain preferred orientation, the electrical and optical properties of ITO films were studied. X-ray diffraction (XRD) patterns indicated that the preferred orientation of film changes from (222) to (400) as T, > 200 degrees C. It can be explained by that the low-index crystallographic planes are easier to be formed when the adatoms have high surface mobility. The Hall measurements indicated that both the concentration and mobility of carrier increase with increasing T,,,. The grain orientation of film does not influence the transmissivity and the carrier concentration, but enhances the carrier mobility. The transmissivity of ITO films is over 90% in the visible wavelength region (except that of the film deposited at 125 degrees C). A minimum resistivity of 5 X 10-4 Omega cm is achieved for the (400) preferred orientation film. Thus, the highest figure of merit of 3.5 x 10(-2) square/Omega is obtained for the film with (400) preferred orientation. The correlation between the preferred orientation and electrical and optical properties are discussed.

(Ga,Mn,N) compounds growth with mass-analyzed low energy dual ion beam deposition

The (Ga,Mn,N) samples were grown by the implantation of low-energy Mn ions into GaN/Al2O3 substrate at different elevated substrate temperatures with mass-analyzed low-energy dual ion beam deposition system. Auger electron spectroscopy depth profile of samples grown at different substrate temperatures indicates that the Mn ions reach deeper in samples with higher substrate temperatures. Clear X-ray diffraction peak from (Ga,Mn)N is observed in samples grown at the higher substrate temperature. It indicates that under optimized substrate temperature and annealing conditions the solid solution (Ga,Mn)N phase in samples was formed with the same lattice structure as GaN and different lattice constant. (C) 2003 Elsevier Science B.V. All rights reserved.

Structural characterization of InGaAs/GaAs quantum dots superlattice infrared photodetector structures

InGaAs/GaAs quantum dots (QDs) superlattice grown by molecular beam epitaxy (MBE) at different substrate temperatures for fabricating 8-12 mu m infrared photodetector were characterized by transmission electron microscopy (TEM), double-crystal X-ray diffraction (DCXRD) and photoluminescence (PL). High-quality QDs superlattice can be achieved by higher growth temperature. Cross-sectional TEM shows the QDs in the successive layers are vertically aligned along growth direction. Interaction of partial vertically aligned columns leads to a perfect vertical ordering. With increasing number of bilayers, the average QDs size becomes larger in height and rapidly saturates at a certain value, while average lateral length nearly preserves initial size. This change leads to the formation of QDs homogeneous in size and of a particular shape. The observed self-organizations are attributed to the effect of strain distribution at QDs on the kinetic growth process. DCXRD measurement shows two sets of satellite peaks which corresponds to QDs superlattice and multi quantum wells formed by the wetting layers. Kinematical simulations of the wetting layers indicate that the formation of QDs is associated with a decrease of the effective indium content in the wetting layers. (C) 1999 Elsevier Science B.V. All rights reserved.

Morphology Evolution of (331)A High-Index Surfaces During Atomic Hydrogen Assisted Molecular Beam Epitaxy (MBE)

Step like morphology of (331)A high-index surfaces during atomic hydrogen assisted molecular beam epitaxy (MBE) growth has been investigated. Atomic Force Microscope (AFM) measurements show that in conventional MBE, the step heights and terrace widths of GaAs layers increase monotonically with increasing substrate temperatures. The terrace widths and step densities increase with increasing the GaAs layer thickness and then saturates. And, in atomic hydrogen assisted MBE, the terrace width reduces and density increases when depositing the same amount of GaAs. It attributes this to the reduced surface migration length of Ga adatoms with atomic hydrogen. Laterally ordered InAs self-aligned nano-wires were grown on GaAs (331)A surfaces and its optical polarization properties were revealed by photoluminescence measurements.