Dielectric properties of Bi2Ti2O7 films grown on Si(100) substrate by APMOCVD

The growth of Bi2Ti2O7 films with (111) orientation on Si(100) substrate by atmospheric pressure metal-organic chemical vapor deposition(APMOCVD) technique at 480similar to550 degreesC is presented. The films were characterized by X-ray diffraction analysis, atomic force microscopy and electron diffraction. The results show high quality Bi2Ti2O7 films with smooth shinning surface. The dielectric properties and C-V characterization of the films were studied. The dielectric constant (epsilon) and loss tangent (tgdelta) were found to be 180 and 0.01 respectively. The charge storage density was 31.9fC/mum(2). The resistivity is higher than 1x10(12) Omega. .cm under the applied voltage of 5V. The Bi2Ti2O7 films are suitable to be used as a new insulating gate material in dynamic random access memory (DRAM).

Transient photoconductivity and its light-induced change of lightly boron-doped a-Si : H films

Transient photoconductivity and its light-induced change were investigated by using a Model 4400 boxcar averager and signal processor for lightly boron-doped a-Si : H films. The transient photoconductivities of the sample were measured at an annealed state and light-soaked states. The transient decay process of the photoconductivity can be fitted fairly well by a second-order exponential decay function, which indicates that the decay process is related with two different traps. It is noteworthy that the photoconductivity of the film increases after light-soaking. This may be due to the deactivity of the boron acceptor B-4(-), and thus some of the boron atoms can no longer act as acceptors and drives E-F to shifts upward. Consequently, the number of effective recombination centers may be reduced and so the photoconductivity increases.

Observation of field-driven blue shift in delta-doped Si n-i-p-i multiple quantum wells

We report the observation of the field-driven blue shift at near absorption edge in the photo-current response spectra of delta-doped Si n-i-p-i multiple quantum wells due to the widening of the effective energy gap. This phenomenon differs from the observed results in GaAs/AlGaAs and GeSi/Si superlattices, because the physical mechanisms of forming energy band in these superlattice samples are different. Our experimental results are interpreted satisfactorily by the theoretical calculation. (C) 1999 Elsevier Science Ltd. All rights reserved.

The effects of carbonized buffer layer on the growth of SiC on Si

Carbonized buffer layers were formed with C2H4 on Si(100) and Si(111) substrates using different methods and SIC epilayers were grown on each buffer layer at 1050 degrees C with simultaneous supply of C2H4 and Si2H6. The structure of carbonized and epitaxy layers was analyzed with in situ RHEED. The buffer layers formed at 800 degrees C were polycrystalline on both Si(100) and Si(111) substrates whereas they were single crystals, with twins on Si(100) and without tu ins on Si(111)substrates. when formed with a gradual rise in substrate temperature from 300 degrees C to growth temperature. Raising the substrate temperature slowly results in the formation of more twins. Epilayers grown on carbonized polycrystalline lavers are polycrystalline. Single crystal epilayers without twins grow on single crystalline buffer layers without twins or with a few twins. (C) 1999 Elsevier Science B.V. All rights reserved.

Growth mode and strain relaxation of InAs on InP (111)A grown by molecular beam epitaxy

Growth mode and strain relaxation of molecular-beam-epitaxy grown InAs/InAlAs/InP (111)A system have been investigated using reflection high-energy electron diffraction, transmission electron microscopy, atomic force microscopy, and photoluminescence measurements. In direct contrast to the well-studied InAs/GaAs system, our experimental results show that the InAs grown on InAlAs/InP (111)A follows the Stranski-Krastanov mode. Both self-organized InAs quantum dots and relaxed InAs islands are formed depending on the InAs coverage. Intense luminescence signals from both the InAs quantum dots and wetting layer are observed. The luminescence efficiency of (111)A samples is comparable to that of (001) samples, suggesting the feasibility of fabricating quantum dot optoelectronic devices on InP (111)A surfaces. (C) 1999 American Institute of Physics. [S0003-6951(99)01010-4].

A study of the interface of CeO2/Si heterostructure grown by ion beam deposition

Epitaxial cerium dioxide films on single-crystal silicon substrates (CeO2/Si) have been grown by a dual mass-analyzed low-energy ion beam deposition (IBD) system. By double-crystal X-ray diffraction (XRD), Full Width at Half Maximum (FWHM) are 23' and 33' in the rocking curves for (222) and (111) faces of the CeO2 film, respectively, and the lattice-mismatch Delta a/a with the substrate is about - 0.123%. The results show that the CeO2/Si grown by IBD is of high crystalline quality. In this work, the CeO2/Si heterostructure were investigated by X-ray Photoelectron Spectroscopy (XPS) and Auger Electron Spectroscopy (AES) measurements. Especially, XPS and AES depth profiling was used to analyze the compositions and structures in the interface regions of the as-grown and post-annealed CeO2/Si. It was found that there was no silicon oxide in the interface region of the as-grown sample but silicon oxide in the post-annealed sample. The reason for obtaining such high quality heterostructure mainly depends on the absence of silicon oxide in the surface at the beginning of the deposition. (C) 1998 Elsevier Science Ltd. All rights reserved.

Wurtzite GaN epitaxial growth on a Si(001) substrate using gamma-Al2O3 as an intermediate layer

Wurtzite GaN films have been grown on (001) Si substrates using gamma-Al2O3 as an intermediate layer by low pressure (similar to 76 Torr) metalorganic chemical vapor deposition. Reflection high energy electron diffraction and double crystal x-ray diffraction measurements revealed that the thin gamma-Al2O3 layer of "compliant" character was an effective intermediate layer for the GaN film grown epitaxially on Si. The narrowest linewidth of the x-ray rocking curve for (0002) diffraction of the 1.3 mu m GaN sample was 54 arcmin. The orientation relationship of GaN/gamma-Al2O3/Si was (0001) GaN parallel to(001) gamma-Al2O3 parallel to(001) Si, [11-20] GaN parallel to[110] gamma-Al2O3 parallel to[110] Si. The photoluminescence measurement for GaN at room temperature exhibited a near band-edge peak of 365 nm (3.4 eV). (C) 1998 American Institute of Physics.

CERIUM SILICIDE FORMATION IN THIN CE SI MULTILAYER FILMS

Alternating layers of Si(200 angstrom thick) and Ce(200 angstrom thick) up to 26 layers altogether were deposited by electron evaporation under ultrahigh vacuum conditions on Si(100) substrate held at 150-degrees-C. Isothermal, rapid thermal annealing has been used to react these Ce-Si multilayer films. A variety of analytical techniques has been used to study these multilayer films after annealing, and among these are Auger electron spectroscopy, Rutherford backscattering, X-ray diffraction, and high resolution transmission electron microscopy. Intermixing of these thin Ce-Si multilayer films has occurred at temperatures as low as 150-degrees-C for 2 h, when annealed. Increasing the annealing temperature from 150 to 400-degrees-C for 1 h, CeSi2 forms gradually and the completion of reaction occurs at approximately 300-400-degrees-C. During the formation of CeSi2 from 150-400-degrees-C, there is some evidence for small grains in the selected area diffraction patterns, indicating that CeSi2 crystallites were present in some regions. However, we have no conclusive evidence for the formation of epitaxial CeSi2 layers, only polycrystals were formed when reacted in the solid phase even after rapid thermal anneal at 900-degrees-C for 10 s. The formation mechanism has also been discussed in combining the results of the La-Si system.

PHOTOEMISSION-STUDY OF THE INTERFACIAL FORMATION PROCESS AND REACTIONS BETWEEN AL AND HYDROGENATED AMORPHOUS SI

Using photoemission spectroscopy and Auger electron spectroscopy, the interfacial formation process and the reactions between Al and hydrogenated amorphous Si are probed, and annealing behaviors of the Al/a-Si:H system are investigated as well. It is found that a three-dimensional growth of Al metal clusters which includes reacted Al and non-reacted metal Al occurs at the initial Al deposition time, reacted Al and Si alloyed layers exist in the Al/a-Si:H interface, and non-reacted Al makes layer-by-layer growth forming a metal Al layer on the sample surface. The interfacial reactions and element interdiffusion of Al/a-Si:H are promoted under the vacuum annealing.

Electron diffraction and photoemission studies of clean and water-covered Si(5,5,12) and Si(112) surfaces

The structure of silicon surfaces in the orientation range (113)-(5,5,12)-(337)-(112) has been investigated using high resolution LEED and photoemission both on a spherical and on flat samples. We find that Si(5,5,12) [5.3 degrees from (113) and 0.7 degrees from (937)] is the only stable orientation between (113) and (111) and confirm the result of Baski et al. [Science 269, 1556 (1995)] that it has a 2 x 1 superstructure with a very large unit cell of 7.68 x 53.5 Angstrom(2). Adsorption measurements of water on Si(5,5,12) yield a mobile precursor kinetics with two kinds of regions saturating at 0.25 and 0.15 ML which are related to adsorption on different sites. Using these results, a modified structure model is proposed. Surfaces between (113) and (5,5,12) separate into facets of these two orientations; between (5,5,12) and (112), they separate into (5,5,12) and (111) facets. (337) facets in this range may be considered as defective (5,5,12) facets.

PLD工艺制备高质量ZnO/Si异质外延薄膜

采用脉冲激光沉积工艺在不同条件下以Si(111)为衬底制备了Zno薄膜.通过对不同氧压下(0～50Pa)沉积的样品的室温PL谱测试表明,氧气氛显著地提高了薄膜的发光质量,在50Pa氧气中沉积的ZnO薄膜具有最强的近带边UV发射.XRD测试说明在氧气氛中得到的薄膜结晶质量较差,没有单一的(002)取向.利用-低温(500℃)沉积的ZnO薄膜作缓冲层,得到了高质量的ZnO外延膜.与直接沉积的ZnO膜相比,生长在缓冲层上的ZnO膜展现出规则的斑点状衍射花样,而且拥有更强的UV发射和更窄的UV峰半高宽(98meV).对不同温度下沉积的缓冲层进行了RHEED表征,结果表明,在600～650℃之间生长缓冲层,有望进一步改善ZnO外延膜的质量.

氧离子束辅助激光淀积生长ZnO/Si薄膜深度剖析

对于在Si(111)上用氧离子束辅助(O~+-assisted)脉冲激光淀积(PLD)生长的ZnO薄膜,用X射线光电子能谱(XPS)深度剖析方法对长成的样品进行了异位测试,分析了导致各峰峰位能移的因素;通过异位与原位XPS谱图的比较,指出O+-assisted PLD法生成的ZnO薄膜中存在孔隙;指出生长出的ZnO薄膜中含si成分的厚度不超过18 nm;同时探讨了在长成的ZnO/Si上继续生长GaN薄膜的可行性.

Si基外延GaN的结构和力学性能

采用MOCVD技术在Si衬底(111)面上生长了GaN外延膜,分析了薄膜表面形貌和Si基GaN的临界载荷,研究了表面发光性能和GaN晶体质量随深度的变化.结果表明,外延层的表面比较平整,多组超晶格插入层可以进一步降低位错密度,提高晶体质量.膜的表面有许多颗粒状的发光中心,除了强的带边峰外,还有弱的黄光带和红光带,这可能是ON与VGa所产生的深能级跃迁产生的.GaN的晶体质量具有梯度变化,GaN外延层的上层晶体质量比较好,界面附近比较差,但是外延层与衬底的结合强度较高,临界载荷达到2.05 N.

Si上外延的n型3C-SiC欧姆接触研究

用LPCVD在si（111）上异质外延了n型3C-SiC，并在所外延的3C-SiC上蒸发Au／Ti，通过不同温度下的RTA（快速热退火）形成欧姆接触。用两种不同的传输线模型对Ti／3C-SiC欧姆接触的ρc（比接触电阻率）进行测量，在750℃退火后Ti／3C-SiC的ρc达到了最低值为3．68×10^-5Ω·cm^2这满足了应用的要求。AES分析结果还表明由于Ti的氧化，更高温度下的退火会使ρc增大。

氧离子束辅助激光淀积生长ZnO/Si的研究

利用X射线衍射(XRD),X射线摇摆曲线(XRC)和X射线光电子能谱(XPS)分析方法对氧离子束辅助激光淀积生长的ZnO/Si异质结薄膜进行了分析.结果表明:用该法可生长出高度c轴单一取向ZnO薄膜,XRC的半高宽度(FWHM)仅为2.918°.表明此生长方法经优化,可生长出单晶质量很好的ZnO/Si薄膜.