光化学气相沉积薄膜的生长机理及其研究进展

近年，作为固体表面一项新的低温成膜工艺，光化学气相沉积已经取得了显著进展。本文从光化学原理角度出发，介绍了光化学气相沉积反应的能量过程及生长机理，并展望了它的今后发展前景。

直流辉光化学气相沉积金刚石的成核密度研究

利用直流辉光等离子体化学气相沉积金刚石的装置,研究了衬底材料以及表面状态对金刚石薄膜成核密度的影响,结果表明金刚石薄膜的成核密度与衬底材料的结合能、晶格常数、对碳的吸附能力及其表面状态有着密切的关系,具有较高结合能和对碳具有较强吸附能力的衬底材料有利于金刚石薄膜的成核。

非晶硅材料及其应用

引言随着科学技术的发展,人们对于自然界物质的认识愈来愈深刻。利用自然资源的能力也越来越高,现在人们不仅能利用晶体材料加工和制造成各种各样的电子器件及用品,而且对非晶体材料也进行了开发和应用,并且已取得了十分显著的成效。本文将对非晶硅材料及其主要应用作扼要介绍。

Material Growth and Device Fabrication of GaN-Based Blue-Violet Laser Diodes

Studies on first GaN-based blue-violet laser diodes(LDs) in China mainland are reported.High quality GaN materials as well as GaN-based quantum wells laser structures are grown by metal-organic chemical vapor deposition method.The X-ray double-crystal diffraction rocking curve measurements show the full-width half maximum of 180″ and 185″ for (0002) symmetric reflection and (10 12) skew reflection,respectively.A room temperature mobility of 850cm2/(V·s) is obtained for a 3μm thick GaN film.Gain guided and ridge geometry waveguide laser diodes are fabricated with cleaved facet mirrors at room temperature under pulse current injection.The lasing wavelength is 405 9nm.A threshold current density of 5kA/cm2 and an output light power over 100mW are obtained for ridge geometry waveguide laser diodes.

科技文摘

渗碳技术规范 R.F.Kern,Heat Treat,Aprit 1989,21,(4),35—37,ISSN0017—9345(英文) 本文分十个部分讨论了渗碳标准技术规范,阐述了每一部分的基本原理。这十部分的主要内容是:硬化;回火;磁粉检验;清洗;深冷却,再加工等。为达到所要求的热处理质量,必须具备正常的热处理设备,以为生产和质量控制。

Analysis and design of resistance-wire heater in MOCVD reactor

Metal organic chemical vapor deposition(MOCVD) is a key equipment in the manufacturing of semiconductor optoelectronic devices and microwave devices in industry. Heating system is a vital part of MOCVD. Specific heating device and thermal control technology are needed for each new reactor design. By using resistance-wire heating MOCVD reaction chamber model, thermal analysis and structure optimization of the reactor were developed from the vertical position and the distance between coils of the resistance-wire heater. It is indicated that, within a certain range, the average temperature of the graphite susceptor varies linearly with the vertical distance of heater to susceptor, and with the changed distances between the coils; furthermore, single resistance-wire heater should be placed loosely in the internal and tightly in the external. The modulate accuracy of the temperature field approximately equals the change of the average temperature corresponding to the change of the coil position.

Laser Processing Mechanism of Monocrystalline Diamond

When a Nd：YAG laser, the wavelength of which is permeable for diamond, is focused on the surface of a diamond sample, a layer of surface material is ablated. Therefore, diamond can be cut by repetitive irradiation. In this study, the processing mechanism of ablation for a single crystal diamond was examined using a heat conduction analysis, considering laser absorption at the surface or the temperature dependence of absorption coefficient. When the laser beam is absorbed at the surface layer, the surface layer is ablated during an early period in the laser pulse. Once the absorption surface layer is ablated, the laser beam penetrates the base material and ablation stops. On the other hand, if the authors assume that single crystal diamond has the temperature dependence of absorption coefficient which is about equal to that of CVD （chemical vapor deposition） diamond, the temperature rise is not enough to ablate the material. However, it became clear that the diamond is ablated deeply when the authors consider both absorption at the surface layer and the temperature dependence of the absorption coefficient. It can be considered that the surface is transformed to graphite and becomes the absorption layer during the repetitive irradiation. It is estimated that the phase change to graphite is very small and its volume fraction is a few percent at most.

Thermal conductivity determination of suspended mono- and bilayer WS2 by Raman spectroscopy

We report the thermal conductivities of monolayer （1L） and bilayer （2L） WS2 grown by chemical vapor deposition （CVD）, which are determined by use of temperature and excitation dependences of E2g^1 and A1g Raman modes. The first-order temperature coefficients of E2g^1 and Alg modes in both supported and suspended WS2 layers were extracted. The frequency shift of the A3g mode with temperature is larger than that of the E1 mode for 1L-WS2, which is 2g attributed to stronger electron-phonon coupling for the A1g mode than that for the E12g mode. Moreover, by use of the shift of the phonon mode induced by laser heating, the thermal conductivities at room temperature were estimated to be 32 and 53 W/（m.K） for 1L- and 2L-WS2, respectively. Our results provide fundamental information about the thermal properties of WS2 layers, which is crucial for developing applications of atomically-thin WS2 devices.

Photoluminescence and surface photovoltage properties of Zn Se nanoribbons

ZnSe nanoribbons were synthesized with chemical vapor deposition route. The excitation power-dependent photol and surface photovoltage （SPV） techniques were used to study the optoelectronic properties of the as-grown ZnSe nanoribbons. Three deep defect （DD）-related emission bands, respectively, centered at 623 nm （DD1）, 563 nm （DD2） and 525 nm （DD3）, emerge orderly with increasing the excitation power, which is attributed to the saturation of the DD states from deeper to shallower level. The SPV spectrum and the corresponding phase spectrum show that DD1 mainly acts as recombination center, while DD2 and DD3 can act as both the recombination center and electron traps. The influence of the trapping electrons on the SPV response dynamic was studied with transient SPV.

Optical contrast determination of the thickness of SiO_2 film on Si substrate partially covered by two-dimensional crystal flakes

SiO_2/Si substrate has been widely used to support two-dimensional （2-D） crystal flakes grown by chemical vapor deposition or prepared by micromechanical cleavage. The visibility of 2-D flakes is very sensitive to the thickness of the SiO_2 layer （hsiO_2）, which can not be determined precisely after the deposit of 2-D flakes. Here, we demonstrated a simple, fast and nondestructive tech- nique to precisely determine hsiO_2 of SiO_2 films on Si substrate only by optical contrast measurement with a typical micro-Raman confocal system. Because of its small lateral resolution down to the micrometer scale, this tech- nique can be used to access hsiO_2 on SiO_2/Si substrate that has been partially covered by 2-D crystal flakes, and then further determine the layer number of the 2-D crystal flakes. This technique can be extended to other dielectric multilayer substrates and the layer-number determination of 2-D crystal flakes on those substrates.

Tailoring the Diameter of Single-Walled Carbon Nanotubes for Optical Applications

Single-walled carbon nanotubes （SWCNTs） with specific diameters are required for various applications particularly in electronics and photonics, since the diameter is an essential characteristic determining their electronic and optical properties. In this work, the selective growth of SWCNTs with a certain mean diameter is achieved by the addition of appropriate amounts of CO2 mixed with the carbon source （CO） into the aerosol （floating catalyst） chemical vapor deposition reactor. The noticeable shift of the peaks in the absorption spectra reveals that the mean diameters of the as-deposited SWCNTs are efficiently altered from 1.2 to 1.9 nm with increasing CO2 concentration. It is believed that CO2 acts as an etching agent and can selectively etch small diameter tubes due to their highly curved carbon surfaces. Polymer-free as-deposited SWCNT films with the desired diameters are used as saturable absorbers after stamping onto a highly reflecting Ag-mirror using a simple dry-transfer technique. Sub-picosecond mode-locked fiber laser operations at -1.56μm and -2 μm are demonstrated, showing improvements in the performance after the optimization of the SWCNT properties.

Direct vapor phase growth process and robust photoluminescence properties of large area MoS2 layers

There has been growing research interest in the use of molybdenum disulfide in the fields of optoelectronics and energy harvesting devices, by virtue of its indirect-to-direct band gap tunability. However, obtaining large area thin films of MoS2 for future device applications still remains a challenge. In the present study, the amounts of the precursors （S and MOO3） were varied systematically in order to optimize the growth of highly crystalline and large area MoS2 layers by the chemical vapor deposition method. Careful control of the amounts of precursors was found to the key factor in the synthesis of large area highly crystalline flakes. The thickness of the layers was confirmed by Raman spectroscopy and atomic force microscopy. The optical properties and chemical composition were studied by photoluminescence （PL） and X-ray photoelectron spectroscopy. The emergence of strong direct excitonic emissions at 1.82 eV （A-exciton, with a normalized PL intensity of -55 × 10^3） and 1.98 eV （B-exciton, with a normalized PL intensity of -5 × 10^3） of the sample at room temperature clearly indicates the high luminescence quantum efficiency. The mobility of the films was found to be 0.09 cm^2/（V.s） at room temperature. This study provides a method for the controlled synthesis of high-quality two-dimensional （2D） transition metal dichalcogenide materials, useful for applications in nanodevices, optoelectronics and solar energv conversion.

Influence of Si co-doping on magnetic, electrical and optical properties of Ga_(1-x)Mn_xN film grown by MOCVD

A detailed study is presented on magnetic, electrical and optical properties of Gal_xMnxN： Si film grown by metal organic chemical vapor deposition （MOCVD） with high-purity Sill4 as the Si dopant source. The room-temperature field dependence magnetization and zero-field-cooled （ZFC）/field-cooled （FC） measurements indicate that the film remains room-temperature ferromagnetism and it declines slightly after Si co-doping. However, room-temperature Hall measurements indicate that the electrical property of the film improves distinctly compared with Gal-xMnxN. Cathode luminescence （CL） measurements show an obvious enhancement in luminous property and different peak strength changes at three different positions. Therefore, we demonstrate that Fermi level and the electron structure of Mn atoms will change with variation of the impurities co-doped and the intrinsic defects and this may be related with room-temperature ferromagnetism and the other corresponding properties of the film.

Kinetics of defect formation in chemically vapor deposited （CVD） graphene during laser irradiation： The case of Raman investigation

The effect of laser irradiation on chemically vapor deposited （CVD） graphene was studied by analyzing the temporal evolution of Raman spectra acquired under various illumination conditions. The spectra showed that the normalized intensity of the defect-related peak increases with the square root of the exposure time and varies almost linearly with the laser power density. Furthermore, the hardness of graphene to radiation damage depends on its intrinsic structural quality. The results suggest that, contrary to the common belief, micro-Raman spectroscopy cannot be considered a noninvasive tool for the characterization of graphene. The experimental observations are compatible with a model that we derived from the interpretative approach of the Staebler-Wronski effect in hydrogenated amorphous silicon; this approach assumes that the recombination of photoexcited carriers induces the breaking of weak C-C bonds.

Laser tuned field emission of the carbon nanotube arrays grown on an optical fiber

Laser was coupled into an optical fiber,on which covered a layer of well-aligned carbon nanotubes(CNTs)serving as cathode,to tune the field emission of the cathode.CNT arrays as field emission cathode were synthesized by chemical vapor deposition(CVD)on a naked fiber core.When the laser was coupled into the fiber,the turn-on voltage(Vto at a current density of 1 mA cm?2)decreased from 1.0 to 0.9 kV and the emission current density increased from 0.83 mA cm?2(at a 1 kV bias voltage)to3.04 mA cm?2 on 40μm diameter fiber.A photon absorption mechanism is attributed to the field emission improvement.The estimated effective work function of CNT arrays on the optical fiber decrease from 4.89 to 4.29 eV.The results show the possibility of constructing a waveguide type laser modulated field emission cathode.

Preparation and characterization of In_(0.82)Ga_(0.18)As PIN photodetectors

Using two-step growth method and buffer layer annealing treatment,the double heterojunction structures of In_(0.82)Ga_(0.18) As epilayer capped with In As_(0.6)P0.4 layer were prepared on In P substrate by low pressure metal organic chemical vapor deposition(LP-MOCVD).Based on the high quality In_(0.82)Ga_(0.18) As structures,the In_(0.82)Ga_(0.18) As PIN photodetector with cut-off wavelength of 2.56 μm at room temperature was fabricated by planar semiconductor technology,and the device performance was investigated in detail.The typical dark current at the reverse bias VR=10 m V and the resistance area product R0 A are 5.02 μA and 0.29 ?·cm2 at 296 K and 5.98 n A and 405.2 ?·cm2 at 116 K,respectively.The calculated peak detectivities of the In_(0.82)Ga_(0.18) As photodetector are 1.21×1010 cm·Hz1/2/W at 296 K and 4.39×1011 cm·Hz1/2/W at 116 K respectively,where the quantum efficiency η=0.7 at peak wavelength is supposed.The results show that the detection performance of In_(0.82)Ga_(0.18) As prepared by two-step growth method can be improved greatly.

Temperature-Dependent Photoconductance of Heavily Doped ZnO Nanowires

Ga-doped ZnO nanowires have been synthesized by a pulsed laser chemical vapor deposition method. The crystal structure and photoluminescence spectra indicate that the dopant atoms are well integrated into the ZnO wurtzite lattice. The photocurrent properties at different temperatures have been systematically investigated for nanowires configured as a three-terminal device. Among the experimental highlights, a pronounced semiconductor-to-metal transition occurs upon UV band-to-band excitation. This is a consequence of the reduction in electron mobility arising from the drastically enhanced Coulomb interactions and surface scattering. Another feature is the reproducible presence of two resistance valleys at 220 and 320 K upon light irradiation. This phenomenon originates from the trapping and detrapping processes in the impurity band arising from the native defects as well as the extrinsic Ga dopants. This work demonstrates that due to the dimensional confinement in quasi-one-dimensional structures, enhanced Coulomb interaction, surface scattering, and impurity states can significantly influence charge transport.