High-Frequency AlGaN/GaN High-Electron-Mobility Transistors with Regrown Ohmic Contacts by Metal-Organic Chemical Vapor Deposition

Nonalloyed ohmic contacts regrown by metal-organic chemical vapor deposition are performed on AlGaN/GaN high-electron-mobility transistors. Low ohmic contact resistance of 0.15Ω.mm is obtained. It is found that the sidewall obliquity near the regrown interface induced by the plasma dry etching has great influence on the total contact resistance. The fabricated device with a 100-nm T-shaped gate demonstrates a maximum drain current density of 0.95 A/mm at Vgs = 1 V and a maximum peak extrinsic transcondutance Gm of 216mS/ram. Moreover, a current gain cut-off frequency fT of 115 GHz and a maximum oscillation frequency fmax of 127 GHz are achieved.

The Effect of Pressure on the Dissociation of H_2/CH_4Gas Mixture during Diamond Films Growth via Chemical Vapor Deposition

Monte Carlo simulations are adopted to study the electron motion in the mixture of H2 and CH4 during diamond synthesis via Glow Plasma-assisted Chemical Vapor Deposition (GPCVD). The non-uniform electric field is used and the avalanche of electrons is taken into account in this simulation. The average energy distribution of electrons and the space distribution of effective species such as CH3, CH+3, CH+ and H at various gas pressures are given in this paper, and optimum experimental conditions are inferred from these results.

Continuous-wave operation of InAs/InP quantum dot tunable external-cavity laser grown by metal-organic chemical vapor deposition

We demonstrate high-performance broadband tunable external-cavity lasers(ECLs) with the metal-organic chemical vapor deposition(MOCVD) grown In As/In P quantum dots(QDs) structures. Without cavity facet coatings, the 3-d B spectral bandwidth of the Fabry–Perot(FP) laser is approximately 10.8 nm, while the tuning bandwidth of ECLs is 45 nm.Combined with the anti-reflection(AR)/high-reflection(HR) facet coating, a 92 nm bandwidth tuning range has been obtained with the wavelength covering from 1414 nm to 1506 nm. In most of the tuning range, the threshold current density is lower than 1.5 k A/cm2. The maximum output power of 6.5 m W was achieved under a 500 m A injection current.All achievements mentioned above were obtained under continuous-wave(CW) mode at room temperature(RT).

Room Temperature and Reduced Pressure Chemical Vapor Deposition of Silicon Carbide on Various Materials Surface

At room temperature, 300 K, silicon carbide film was formed using monomethylsilane gas on the reactive surface prepared using argon plasma. Entire process was performed at reduced pressure of 10 Pa in the argon plasma etcher, without a substrate transfer operation. By this process, the several-nanometer-thick amorphous thin film containing silicon-carbon bonds was obtained on various substrates, such as semiconductor silicon, aluminum and stainless steel. It is concluded that the room temperature silicon carbide thin film formation is possible even at significantly low pressure, when the substrate surface is reactive.

Improved Semipolar(11(2|-)2) GaN Quality Grown on m-Plane Sapphire Substrates by Metal Organic Chemical Vapor Deposition Using Self-Organized SiN_x Interlayer

The effect of a self-organized SiNs interlayer on the defect density of （1122） semipolar GaN grown on 7n-plane sapphire is studied by transmission electron microscopy, atomic force microscopy and high resolution x-ray diffrac- tion. The SiNx interlayer reduces the c-type dislocation density from 2.5 ×10^10 cm^-2 to 5 ×10^8 cm 2. The SiNx interlayer produces regions that are free from basal plane stacking faults （BSFs） and dislocations. The overall BSF density is reduced from 2.1×10^5 cm-1 to 1.3×10^4 cm^-1. The large dislocations and BSF reduction in semipolar （1122） GaN with the SiNx, interlayer result from two primary mechanisms. The first mechanism is the direct dislocation blocking by the SiNx interlayer, and the second mechanism is associated with the unique structure character of （1122） semipolar GaN.

Effect of pressure on the semipolar GaN(10-11) growth mode on patterned Si substrates

In this paper, we investigate the effect of pressure on the growth mode of high quality （10-11） GaN using an epi- taxial lateral over growth （ELO） technique by metal organic chemical vapor deposition （MOCVD）. Two pressure growth conditions, high pressure （HP） 1013 mbar and low pressure growth （LP） 500 mbar, are employed during growth. In the high pressure growth conditions, the crystal quality is improved by decreasing the dislocation and stack fault density in the strip connection locations. The room temperature photoluminescence measurement also shows that the light emission intensity increases three times using the HP growth condition compared with that using the LP growth conditions. In the low temperature （77 K） photoluminescence, the defects-related peaks are very obvious in the low pressure growth samples. This result also indicates that the crystal quality is improved using the high pressure growth conditions.

Growth of large-area atomically thin MoS2 film via ambient pressure chemical vapor deposition

Atomically thin MoS2 films have attracted significant attention due to excellent electrical and optical properties.The development of device applications demands the production of large-area thin film which is still an obstacle.In this work we developed a facile method to directly grow large-area MoS2 thin film on Si O2 substrate via ambient pressure chemical vapor deposition method. The characterizations by spectroscopy and electron microscopy reveal that the as-grown MoS2 film is mainly bilayer and trilayer with high quality. Back-gate field-effect transistor based on such MoS2 thin film shows carrier mobility up to 3.4 cm2V-1s-1 and on/off ratio of 105. The large-area atomically thin MoS2 prepared in this work has the potential for wide optoelectronic and photonic device applications.

Cleaning of nitrogen-containing carbon contamination by atmospheric pressure plasma jet

Atmospheric pressure plasma jet(APPJ)was used to clean nitrogen-containing carbon films(C–N)fabricated by plasma-assisted chemical vapor deposition method employing the plasma surface interaction linear device at Sichuan University(SCU-PSI).The properties of the contaminated films on the surface of pristine and He-plasma pre-irradiated tungsten matrix,such as morphology,crystalline structure,element composition and chemical structure were characterized by scanning electron microscopy,grazing incidence x-ray diffraction and x-ray photoelectron spectroscopy.The experimental results revealed that the removal of C–N film with a thickness of tens of microns can be realized through APPJ cleaning regardless of the morphology of the substrates.Similar removal rates of 16.82 and 13.78μm min^(-1)were obtained for C–N films deposited on a smooth pristine W surface and rough fuzz-covered W surface,respectively.This is a remarkable improvement in comparison to the traditional cleaning method.However,slight surface oxidation was found after APPJ cleaning,but the degree of oxidation was acceptable with an oxidation depth increase of only 3.15 nm.Optical emission spectroscopy analysis and mass spectrometry analysis showed that C–N contamination was mainly removed through chemical reaction with reactive oxygen species during APPJ treatment using air as the working gas.These results make APPJ cleaning a potentially effective method for the rapid removal of C–N films from the wall surfaces of fusion devices.

Structure and Electrical Characteristics of Zinc Oxide Thin Films Grown on Si (111) by Metal-organic Chemical Vapor Deposition

ZnO thin films were grown on Si （111） substrates by low-pressure metal-organic chemical vapor deposition. The crystal structures and electrical properties of as-grown sample were investigated by scanning electron microscopy （SEM） and conductive atomic force microscopy （C-AFM）. It can be seen that with increasing growth temperature, the surface morphology of ZnO thin films changed from flake-like to cobblestones-like structure. The current maps were simultaneously recorded with the topography, which was gained by C-AFM contact mode. Conductivity for the off-axis facet planes presented on ZnO grains enhanced. Measurement results indicate that the off-axis facet planes were more electrically active than the c-plane of ZnO flakes or particles probably due to lower Schottky barrier height of the off-axis facet planes.

Characterization of the heteroepitaxial growth of 3C-SiC on Si during low pressure chemical vapor deposition

3C-SiC heteroepitaxial layers were grown on Si substrates using a horizontal,hot-wall low pressure chemical vapor deposition system.The crystal quality,surface morphology and thickness uniformity of the layers were characterized by X-ray diffraction,atomic force microcopy and Fourier transform infrared spectroscopy,respectively.Growth of the epitaxial layer was determined to follow a three-dimensional island mode initially and then switch to a step-flow mode as the growth time increases.

Arc Discharge Device Working at Atmospheric Pressure

Arc in vacuum is one of the important methods used to prepare carbon materials. However, the use of vacuum increases the cost of the arc method. This paper introduces an arc discharge device working at atmospheric pressure. The current-limiting resistor, capacitor and inductor make the discharge gentle. The electrode temperature can be adjusted from 2040 K to 3673 K. Carbon nanofibres were prepared at the electrode temperature of 3645 K by using this device.

Characterization of Crystalline Nanoparticles/Nanorods Synthesized by Atmospheric Plasma Enhanced Chemical Vapor Deposition of Perfluorohexane

A mass of nanoparticles/nanorods were formed on a simultaneously deposited gran- ular film by plasma enhanced chemical vapor deposition （PECVD） of perfluorohexane at atmo- spheric pressure without any catalysts or templates. Scanning electron microscopy （SEM） and X-ray photoelectron spectroscopy （XPS） were used to characterize the morphology and the chem- ical compositions of nanoparticles. The average size of particles is about 100 nm and the length of synthesized nanorods is between 1 μm and 2.5/tm. The analyses of transmission electron microscopy （TEM）, high-resolution transmission electron microscopy （HRTEM）, selected area electron diffraction（SAED） and X-ray diffraction （XRD） reveals that the nanoparticles and nanorods are crystalline.

Low-Temperature Growth of ZnO Films on GaAs by Metal Organic Chemical Vapor Deposition

ZnO thin films were grown on GaAs （001） substrates by metal-organic chemical vapor deposition （MOCVD） at low temperatures ranging from 100 to 400℃. DEZn and 1-12 O were used as the zinc precursor and oxygen precursor, respectively. The effects of the growth temperatures on the growth characteristics and optical properties of ZnO films were investigated. The X-ray diffraction measurement （XRD） results indicated that all the thin films were grown with highly c- axis orientation. The surface morphologies and crystal properties of the films were critically dependent on the growth temperatures. Although there was no evidence of epitaxial growth, the scanning electron microscopy （SEM） image of ZnO film grown at 400℃ revealed the presence of ZnO microcrystallines with closed packed hexagon structure. The photoluminescence spectrum at room temperature showed only bright band-edge （3. 33eV） emissions with little or no deep-level e- mission related to defects.

Chemical Vapor Deposition Mechanism of Copper Films on Silicon Substrates

A versatile metal-organic chemical vapor deposition （MOCVD） system was designed and constructed. Copper films were deposited on silicon （100） substrates by chemical vapor deposition （CVD） using Cu（hfac）2 as a precursor. The growth of Cu nucleus on silicon substrates by H2 reduction of Cu（hfac）2 was studied by atomic force microscopy and scanning electron microscopy. The growth mode of Cu nucleus is initially Volmer-Weber mode （island）, and then transforms to Stranski-Rastanov mode （layer-by-layer plus island）. The mechanism of Cu nucleation on silicon （100） substrates was further investigated by X-ray photoelectron spectroscopy. From Cu2p, O1s, F1s, Si2p patterns, the observed C=O, OH and CF3/CF2 should belong to Cu（hfac） formed by the thermal dissociation of Cu（hfac）2. H2 reacts with hfac on the surface, producing OH. With its accumulation, OH reacts with hfac, forming HO-hfac, and desorbs, meanwhile, the copper oxide is reduced, and thus the redox reaction between Cu（hafc）2 and H2 occurs.

Mid-gap photoluminescence and magnetic properties of GaMnN films grown by metal–organic chemical vapor deposition

Metal-organic chemical vapor deposition （MOCVD） grown ferromagnetic GaMnN films are investigated by photo- luminescence （PL） measurement with a mid-gap excitation wavelength of 405 nm. A sharp PL peak at 1.8 eV is found and the PL intensity successively decreases with the addition of Mn, in which the Mn concentration of sample A is below 1% （[Mn]A =0.75%） but its PL intensity is stronger than other samples＇. The 1.8-eV PL peak is attributed to the recombination of electrons in the t2 state of the neutral Mn3＋ acceptor with holes in the valence band. With Mn concentration increasing, the intensity of the PL peak decreases and the magnetic increment reduces in our samples. The correlation between the PL peak intensity and ferromagnetism of the samples is discussed in combination with the experimental results.

Metal-organic Chemical Vapor Deposition of GaSb/GaAs Quantum Dots： the Dependence of the Morphology on Growth Temperature and Vapour V/Ⅲ Ratio

GaSb quantum dots have been widely applied in optoelectronic devices due to its unique electrical and optical properties.The effects of metal-organic chemical vapor deposition（MOCVD） parameters,such as growth temperature and vapour V/Ⅲ ratio[V/Ⅲ ratio means the molar ratio of trimethylgallium（TMGa） and triethylantimony（TESb）],were systematically investigated to achieve GaSb quantum dots with high quality and high density.The features of surface morphology of uncapped GaSb quantum dots were characterized by atomic force microscope（AFM） images.The results show that the surface morphologies of quantum dots are strongly dependent on growth temperature and vapour V/Ⅲ ratio.GaSb quantum dots with an average height of 4.94 nm and a density of 2.45× 1010 cm-2 were obtained by optimizing growth temperature and V/Ⅲ ratio.

Preparation of rutile TiO_(2) thin films by laser chemical vapor deposition method

TiO_(2) thin films were prepared on Pt/Ti/SiO_(2)/Si substrate by laser chemical vapor deposition(LCVD)method.The effects of laser power(P_(L))and total pressure(p_(tot))on the microstructure of TiO_(2) thin films were investigated.The deposition temperature(T_(dep))was mainly affected by P_(L),increasing with P_(L) increasing.The single-phase rutile TiO_(2) thin films with different morphologies were obtained.The morphologies of TiO_(2) thin films were classified into three typical types,including the powdery,Wulff-shaped and granular microstructures.p_(tot) and T_(dep) were the two critical factors that could be effectively used for controlling the morphology of the films.

基于大厚度六方氮化硼中子探测器的制备

六方氮化硼是一种中子敏感材料。介绍了使用低压气相化学沉积在1673K下以大约20μm/h的生长速率制备了高质量203μm厚的六方氮化硼。在氮化硼的两侧沉积厚度为100nm的金电极,制备了垂直结构的六方氮化硼中子探测器。该器件的电学性质表明制备的六方氮化硼材料的迁移率寿命的乘积(μτ)为2.8×10^(-6)cm^(2)/V,电阻率为1.5×10^(14)Ω·cm。在850V电压下,该探测器对热中子的探测效率为34.5%,电荷收集效率为60%。

重掺硅片表面APCVD法生长SiO_(2)薄膜的致密性

在硅片加工过程中,金属杂质的存在会增大pn结器件的漏电流,甚至直接导致pn结禁带宽度变窄,为防止出现硅外延过程中造成的自掺杂现象,通常在硅片表面生长一层高致密性的SiO_(2)薄膜。基于常压化学气相沉积(APCVD)法在6英寸(1英寸≈2.54 cm)n型硅片表面生长SiO_(2)薄膜,首先研究不同沉积温度、SiH_(4)和O_(2)的体积流量比对沉积速率和SiO_(2)薄膜致密性的影响,进一步探究了不同退火温度对SiO_(2)薄膜致密性的影响,以期获得致密性较高的SiO_(2)薄膜。采用HF腐蚀速率法表征其致密性,采用扫描电子显微镜(SEM)观察SiO_(2)薄膜的表面形貌,采用F50膜厚测试仪测试SiO_(2)薄膜的厚度。结果表明,沉积温度为400℃,SiH_(4)和O_(2)的体积流量比为1∶10,退火温度为1100℃时,制备的SiO_(2)薄膜的致密性为0.096 nm/s(采用体积分数为1%的HF腐蚀)。

8英寸晶圆低损耗厚氮化硅波导的工艺开发

在8英寸晶圆上制备氮化硅膜厚度超过400 nm时,产生的拉伸应力会使薄膜产生裂纹,为此,采用大马士革工艺,通过低压化学气相沉积分两步沉积、抛光氮化硅薄膜,同时结合棋盘格结构,减小应力,降低薄膜出现裂纹的风险。使用此方法成功在8英寸晶片上制造了截面尺寸为800 nm×0.8µm的氮化硅波导。两步沉积过后进行两次退火处理,可以进一步降低波导损耗,通过采用cut-back的方式测试波导传输损耗在1550 nm处为0.087 dB/cm,在1580 nm处为0.062 dB/cm。波导的弯曲损耗在半径为50µm时为0.0065 dB,在半径为80µm时仅为0.006 dB。