Preparation of LiNbO_3 films on Si(111) substrates by a modified sol-gel process

The preparation of LiNbO 3 films on Si substrates was improved by adding CH 3CH 2OH solution containing a little water to the sol of LiNb(OC 2H 5) 6. The crystallization behavior of LiNbO 3 films on Si (111) substrates was studied and completely c axis oriented LiNbO 3 films were obtained. Such factors as the hydrogen termination of silicon surface, the RTP annealing process used, the unidirectional heat flow and the preheating temperature were taken into consideration while the crystallization of c axis oriented films was analysed. Surface morphologies of the films annealed in RTP and conventional furnaces were observed by means of AFM.

Reactive Magnetron Sputtering of CN_x Thin Films on β-Si_3N_4 Substrates

Carbon nitride CN. thin films have been deposited on polycrystalline β-Si3N4 substrates by un-balanced magnetron sputtering in a nitrogen discharge. Both the film deposition rate and the nitrogen concentration decrease with substrate temperature increase in the range of 100~400℃The maximum of nitrogen content is 40 at. pct. Raman spectroscopy and atomic force mi-croscopy were used to characterize the bonding, microstructure and surface roughness of the films. Nanoindentation experiments exhibit a higher hardness of 70 GPa and an extremely elas-tic recovery of 85% at higher substrate temperature.

Preparation of c-Axis Oriented LiNb_(1-x) Ta_xO_3 Films on Si(111) Substrates by a Modified Sol-gel Process

In this work, we succeeded in the preparation of LiNb 1- x Ta x O 3 films on Si(111) substrates by means of sol gel process, and the usual sol gel process for the preparation of LiNbO 3 and LiTaO 3 films on Si substrates was improved by adding a 33% aqueous solution of CH 3CH 2OH to the mixed sols of LiNb(OCH 2CH 3) 6 and LiTa(OCH 2CH 3) 6 . The crystallization behavior of LiNb 1- x Ta x O 3 films on Si(111) substrates has been studied. Highly c axis oriented LiNb 1- x Ta x O 3 films have been obtained within the tantalum composition range of \{0< x <0 33\}. Some factors such as the hydrogen termination of the silicon surface, the RTP annealing process that provides the unidirectional heat flow and the preheating temperature are discussed to analyze the crystallization of the c axis oriented films.

The Research on Growth Temperature of Ge/Si Thin Films Grown by Magnetron Sputtering

The films of Ge and Si were grown on the substrate Si (100) by magnetron sputtering at 2.5 Pa Ar pressure.The growth temperature of films was 100℃,250℃,400℃and 550℃.The structure and composition were analysised by Raman scattering.The poly-crystal peak and crystal peak of Ge were observed in these films.The results indicate that the single crystal film of Ge was prepared at the substrate temperature of 400℃.The peak of acoustic phonons of Ge was 98 cm^(-1) and that of Si was 170 cm^(-1).

Effects of high temperature rapid thermal annealing on Ge films grown on Si(001) substrate

Tensile strain, crystal quality, and surface morphology of 500 nm thick Ge films were improved after rapid thermal annealing at 900 ℃ for a short period （〈 20 s）. The films were grown on Si（001） substrates by ultra-high vacuum chemical vapor deposition. These improvements are attributed to relaxation and defect annihilation in the Ge films. However, after prolonged （〉 20 s） rapid thermal annealing, tensile strain and crystal quality degenerated. This phenomenon results from intensive Si-Ge mixing at high temperature.

Preparation and characterization of GaN films grown on Ga-diffused Si (111) substrates

Hexagonal GaN films were prepared by nitriding Ga_2O_3 films with flowingammonia. Ga_2O_3 films were deposited on Ga-diffused Si (111) substrates by radio frequency (r.f.)magnetron sputtering. This paper have investigated the change of structural properties of GaN filmsnitrided in NH_3 atmosphere at the temperatures of 850, 900, and 950 deg C for 15 min and nitridedat the temperature of 900 deg C for 10, 15, and 20 min, respectively. X-ray diffraction (XRD),scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectronspectroscopy (XPS) were used to analyze the structure, surface morphology and composition ofsynthesized samples. The results reveal that the as-grown films are polycrystalline GaN withhexagonal wurtzite structure and GaN films with the highest crystal quality can be obtained whennitrided at 900 deg C for 15 min.

Laser Direct Writing of Ag Films from Solution on Si Substrate

Pulsed Nd:YAG laser was used to irradiate Si substrate immersed in AgNO3 ethylene glycol solution to deposit Ag films along the lines scanned by laser on the substrate, which is a photo-thermal decomposing process. The decomposed Ag atoms congregate and form polycrystalline Ag particles. The Ag concentration changes greatly with the total laser energyA absorbed by substrate. Transmission electron microscopy (TEM) observation shows the Ag particles are inlaid in the Si substrate. Auger electron spectrum (AES) shows that the Ag concentration decreases with the increase of the sputtering depth, and there is no oxygen element on the surface of the deposited Ag films.

Effects of Annealing Temperature on Properties of ZnO Thin Films Grown by Pulsed Laser Deposition

ZnO thin films are deposited on n-Si（111） substrates by pulsed laser deposition（PLD） system. Then the samples are annealed at different temperatures in air ambient and their properties are investigated particularly as a function of annealing temperature. The microstructure, morphology and optical properties of the as-grown ZnO films are studied by X-ray diffraetion（XRD）. atomic force mieroseope（AFM）, Fourier transform infrared spectroscopy（FTIR） and photoluminescence（PL） spectra. The results show that the as- grown ZnO films have a hexagonal wurtzite structure with a preferred c-axis orientation. Moreover, the diameters of the ZnO crystallites become larger and the crystal quality of the ZnO fihns is improved with the increase of annealing temperature.

Structure and Strain Properties of GaN Films Grown on Si（111） Substrates with AlxGa1-xN/AlyGa1-yN Superlattices

CaN films with an AlxGa1-xN/AlyGa1-xN superlattice （SL） buffer layer are grown on Si（111） substrates by metal-organic chemical vapor deposition （MOCVD）. The structure and strain properties of the samples are studied by optical microscopy, Raman spectroscopy, x-ray diffractometry and atomic force microscopy. The results show that the strain status and crystalline quality of the CaN layers are strongly dependent on the difference of the Al composition between AlxCa1-xN barriers and AlyCa1-yN wells in the SLs. With a large Al composition difference, the CaN film tends to generate cracks on the surface due to the severe relaxation of the SLs. Otherwise, when using a small Al composition difference, the crystalline quality of the CaN layer degrades due to the poor function of the SLs in filtering dislocations. Under an optimized condition that the Al composition difference equals 0.1, the crack-free and compressive strained CaN film with an improved crystalline quality is achieved. Therefore, the AlxGa1-xN/AlyGal-yN SL buffer layer is a promising buffer structure for growing thick CaN films on Si substrates without crack generation.

Effects of Substrate Temperature on the Growth of Polycrystalline Si Films Deposited with SiH_4+Ar

Polycrystalline silicon （poly-Si） films were deposited using Ar diluted SiH4 gaseous mixture by electron cyclotron resonance plasma-enhanced chemical vapor deposition （ECR-PECVD）. The effects of the substrate temperature on deposition rate, crystallinity, grain size and the configuration of H existing in poly-Si film were investigated. The results show that, comparing with H2 dilution, Ar dilution could significantly decrease the concentration of H on the growing surface. When the substrate temperature increased, the deposition rate increased and the concentration of H decreased monotonously, but the crystallinity and the grain size of poly-Si films exhibited sophisticated trends. It is proposed that the crystallinity of the films is determined by a competing balance of the self-diffusion activity of Si atoms and the deposition rate. At substrate temperature of 200℃, the deposited film exhibits the maximum poly-Si volume fraction of 79%. Based on these results, higher substrate temperature is suggested to prepare the poly-Si films with advanced stability and compromised crystallinity at high deposition rate.

Preparation of BiFeO_3 thin films by pulsed laser deposition method

BiFeO3 (BFO) thin films were prepared on Pt(111)/TiO2/SiO2/Si(100) substrates by the pulsed-laser deposition (PLD) technique at a low temperature of 450℃. The XRD results indicate that the BFO thin films are of perovskite structure with the presence of small amount of second phases. The oxygen pressures have great effect on the crystalline structures and dielectric properties of BFO thin films. The dielectric constant of the BFO thin films decreases with increasing oxygen pressures, achieving 186, 171 and 160 at the frequency of 104 Hz for the oxygen pressures of 0.666, 1.333 and 13.332 Pa, respectively. The BFO thin films prepared at the oxygen pressure of 0.666 Pa reveal a saturated hysteresis loop with the remanent polarization of 7.5 μC/cm2 and the coercive field of 176 kV/cm.

Growth of MgO Thin Film on Silicon Substrate by MOCVD

Highly oriented MgO(111)and MgO(100)thin films have been deposited on Si(111)and Si(100)substrates by using Low Pressure MOCVD(LPMOCVD).Magnesium 2,4-pentanedionate was used as the source ma- terial.The films have a very smooth surface morphology and optical transparency with an index of refraction of 1.71(632.8 nm).Typical growth rate of the films is 1.0 μm/h.The data of X-ray diffraction analysis indi- cate that the films are fully textured with(111)and(100)orientation perpendicular to the substrate surface respectively.The main parameters having influence on the deposition are the substrate temperature,the total pressure in the reaction chamber,the reaction gases and its flowrate.

PREPARATION OF LN_2 TEMPERATURE REGION SUPERCONDUCTOR FILM ON Si(100) SUBSTRATE

Expermental results of the preparation of YBaCuO superconductor thin film on Si(100) substrate by the method of ion beam sputtering deposition is presented.A ZrO_2 buffer layer was applied to Si(100)substrate,and was found to play an important role in resisting the diffusion of Si toward the film.The thin film is mainly a 123 phase with strong c-axis prefer- red orientation.The onset transition temperature of the film is 100 K and the final transition temperature 78 K.

a-Si/c-Si heterojunction solar cells on SiSiC ceramic substrates

Silicon thin-film solar cells are considered to be one of the most promising cells in the future for their potential advantages, such as low cost, high efficiency, great stability, simple processing, and none-pollution. In this paper, latest progress on poly-crystalline silicon solar cells on ceramic substrates achieved by our group was reported. Rapid thermal chemical vapor deposition (RTCVD) was used to deposited poly-crystalline silicon thin films, and the grains of as-grown film were enlarged by Zone-melting Recrystallization (ZMR). As a great change in cell′s structure, traditional diffused pn homojunction was replaced by a-Si/c-Si heterojunction, which lead is to distinct improvement in cell′s efficiency. A conversion efficiency of 3.42% has been achieved on 1 cm2 a-Si/c-Si heterojunction solar cell (Isc=16.93 mA, Voc=310.9 mV, FF=0.6493, AM=1.5 G, 24 ℃), while the cell with diffused homojunction only got an efficiency of 0.6%. It indicates that a-Si emitter formed at low temperature might be more suitable for thin film cell on ceramics.

Elimination of Crystallographic Wing Tilt of Canti-Bridged Epitaxial Laterally Overgrown GaN Films by Optimizing Growth Procedure

Canti-bridged epitaxial lateral overgrowth （CBELO） of GaN is performed by metalorganic chemical vapour deposition （MOCVD） on maskless V-grooved sapphire substrates prepared by wet chemical etching with different mesa widths. The wing tilt usually observed in ELO is not found in the CBELO GaN with wide mesa widths, while it can be detected obviously in the GaN with narrow mesa widths. The wing tilt of CBELO GaN grown on a grooved sapphire substrate with narrow mesa can be controlled by adjusting the thickness of the nucleation layer. The dependence of the wing tilt on the nucleation layer thickness is studied. Cross-sectional scanning electron microscopy is used to characterize the geometry of the wing regions, and double crystal x-ray diffraction is used to analyse the structural characteristics and to measure the magnitude of the crystalline wing tilt. It is found that the crystalline wing tilt can be eliminated completely by first growth of a thin nucleation GaN layer then the CBELO GaN. Possible reason and the origin of the wing tilt in CBELO GaN films are also discussed.

Ultraviolet and Deep-Ultraviolet Emissions from c-MgxZn1-xO/MgO Ultrathin Multilayer Heterostructures

Cubic phase MgxZn1-x O/MgO multilayer heterostructures （c-Mgx Zn1-xO/MgO MHs） are grown on Si（100） and quartz substrates by reactive electron beam evaporation at low temperature （250℃）. Cross-sectional morphology observations by field-emission scanning electron microscopy show the legible interfaces of c-MgxZn1-x O/MgO MHs. X-ray diffraction demonstrates that c-MgxZn1-xO/MgO MHs are of highly （100）-oriented. Optical trans- mission investigations of c-Mgx Zn1-x O/MgO MHs on quartz substrates reveal the coexistence of the two phases, c-MgxZn1-xO and MgO. Photoluminescence examination indicates the emergence of deep-ultraviolet emission centred at about 290nm along with the blue shift of the ultraviolet emission from 405nm to 39Gnm when the nominal thickness of c-MgxZn1-xO well layers of MHs is diminished to 3nm, which is probably originated from quantum confinement effect.

热丝CVD法在单晶硅衬底上低温外延生长Si和Ge薄膜的研究

采用热丝CVD法在单晶Si衬底上进行了Si和Ge薄膜的低温外延生长,用XRD和Raman谱对其结构性能进行了分析。结果表明:在衬底温度200℃时,Si(111)单晶衬底上外延生长出了Raman峰位置为521.0cm-1;X射线半峰宽(FWHM)为5.04cm-1。结晶质量非常接近于体单晶的(111)取向的本征Si薄膜;在衬底温度为300℃时,在Si(100)单晶衬底上异质外延,得到了Raman峰位置为300.3cm-1的Ge薄膜,Ge薄膜的晶体取向为Ge(220)。研究表明热丝CVD是一种很好的低温外延薄膜的方法。

离子束溅射制备Si/Ge多层膜的结晶研究

采用离子束溅射制备Si/Ge多层膜,通过X射线小角衍射计算其周期厚度及各子层的厚度,用Raman光谱对Si/Ge多层膜的微观结构及Si子层的结构进行表征。结果表明,所制备的Si/Ge多层膜中,当Ge子层的厚度为6. 2nm时, Si子层的结晶质量较好,表明适量的Ge含量有诱导Si结晶的作用。

Ge/Si薄膜材料生长的偏压效应研究

利用超高真空磁控溅射系统生长了不同偏压下Ge/Si薄膜材料 ,所生长的材料采用了不加偏压和加偏压的生长环境。通过X射线小角衍射分析表明 ,加一定偏压的Ge/Si薄膜材料的层状远比不加偏压的材料好 ,并且加偏压可有效降低材料的生长温度。在加 15～ 2 5V偏压时 ,获得了 30 0℃的生长温度下 ,层状优良 。

LPCVD-SiGe薄膜的物理及电学特性

采用低压化学气相沉积法(LPCVD),分别在n-Si和SiO2衬底上制备Si1-xGex薄膜。Ge的组分比由俄歇电子谱(AES)测定。对n-Si和SiO2衬底上的Si1-xGex分别进行热扩散和热退火处理,以考察热扩散和退火条件对薄膜物理及电学特性的影响。薄膜的物相由X射线衍射(XRD)确定。其薄层电阻、载流子迁移率及浓度分别由四探针法和霍尔效应法测定。基于XRD图谱,根据Scherer公式,估算出平均晶粒大小。数值拟合得到霍尔迁移率与平均晶粒尺寸为近似的线性关系,从而得出LPCVD-Si1-xGex薄膜的电输运特性基本符合Seto模型的结论。