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1.
2.
We have studied luminescence properties and microstructure of 20 patterns Si/SiO2 multilayers. The photoluminescence spectra consist of two gaussian bands in the visible-infrared spectral region. It has been demonstrated that the strong PL band is caused by the radiative recombination in the Si/SiO2 interfaces states, whereas the weaker band originates from radiative recombination in the nanosized Si layers. The peak shift of this latter band shows a discontinuity that corresponds to a crystalline-to-amorphous phase change when the Si layers are thinner than 30 Å. The peak energy as a function of the layer thickness is interpreted using a quantum confinement model in the case of amorphous Si layers.  相似文献   

3.
In this work, anodic porous alumina thin films with pores in the nanometer range are grown on silicon by electrochemistry and are used as masking material for the nanopatterning of the silicon substrate. The pore diameter and density are controlled by the electrochemical process. Through the pores of the alumina film chemical oxidation of the silicon substrate is performed, leading to the formation of regular arrays of well-separated stoichiometric silicon dioxide nanodots on silicon, with a density following the alumina pores density and a diameter adjustable by adjusting the chemical oxidation time. The alumina film is dissolved chemically after the SiO2 nanodots growth, revealing the arrays of silicon dioxide dots on silicon. In a next step, the nanodots are also removed, leaving a nanopatterned bare silicon surface with regular arrays of nanopits at the footprint of each nanodot. This silicon surface structuring finds interesting applications in nanoelectronics. One such application is in silicon nanocrystals memories, where the structuring of the oxidized silicon surface leads to the growth of discrete silicon nanocrystals of uniform size. In this work, we examine the electrical quality of the Si/SiO2 interface of a nanostructured oxidized silicon surface fabricated as above and we find that it is appropriate for electronic applications (an interface trap density below 1–3×1010 eV−1 cm−2 is obtained, indicative of the high quality of the thermal silicon oxide).  相似文献   

4.
马书懿  萧勇  陈辉 《中国物理》2002,11(9):960-962
The structure of Au/Si/SiO2/p-Si has been fabricated using the magnetron sputtering technique. It has a very good rectifying behaviour. Visible electroluminescence (EL) has been observed from the Au/Si/SiO2/p-Si structure at a forward bias of 5V or larger. A broad band with one peak around 650-660 nm appears in all the EL spectra of the structure. The effects of the thickness of the Si layer in the Si/SiO2 films and of the input electrical power on EL spectra are studied systematically.  相似文献   

5.
The degradation of the cathodoluminescence (CL) intensity of cerium-doped yttrium silicate (Y2SiO5:Ce) phosphor powders was investigated for possible application in low voltage field emission displays (FEDs). Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS) and CL spectroscopy were used to monitor changes in the surface chemical composition and luminous efficiency of commercially available Y2SiO5:Ce phosphor powders. The degradation of the CL intensity for the powders is consistent with a well-known electron-stimulated surface chemical reaction (ESSCR) model. It was shown with XPS and CL that the electron stimulated reaction led to the formation of a luminescent silicon dioxide (SiO2) layer on the surface of the Y2SiO5:Ce phosphor powder. XPS also indicated that the Ce concentration in the surface layer increased during the degradation process and the formation of CeO2 and CeH3 were also part of the degradation process. The CL intensity first decreased until about 300 C cm−2 and then increased due to an extra peak arising at a wavelength of 650 nm.  相似文献   

6.
We investigate the stability of boron dopants near the interface between crystalline Si and amorphous SiO2 through first-principles density functional calculations. An interstitial B is found to be more stable in amorphous SiO2 than in Si, so that B dopants tend to segregate to the interface. When defects exist in amorphous SiO2, the stability of B is greatly enhanced, especially around Si floating bond defects, while it is not significantly affected near Si–Si dimers, which are formed by O-vacancy defects.  相似文献   

7.
The structural degradation of thermal SiO2 on (100)Si under isochronal post oxidation vacuum annealing (POVA) has been probed by electron spin resonance (ESR). The degradation process, studied in the range Tan = 950–1250 °C, is established as intense point defect generation including E′γ, E′δ, EX and the elusive predominant degradation center S. Thermally activated generation is revealed over broad Tan ranges for the two most populous defects, S and E′γ, with a common activation energy ~1.6eV. Depth profiling after heating at 1200°C shows that the S centers predominantly reside near the oxide borders, generally in anticorrelation with the E′γ distribution. The S center susceptibility has been inferred from conventional ESR signal intensity monitoring as well as from revealed anisotropic demagnetisation effects. It is found Curie-Weiss type with critical temperature of ~ 1.3 K. Newly observed weak hyperfine structure may comply with the S center being an E′-like defect.  相似文献   

8.
Structural and optical properties of Si/SiO2 multi-quantum wells (MQW) were investigated by means of Raman scattering and photoluminescence (PL) spectroscopy. The MQW structures were fabricated on a quartz substrate by remote plasma enhanced chemical vapour deposition (RPECVD) of alternating amorphous Si and SiO2 layers. After layer deposition the samples were subjected to heat treatments, i.e. rapid thermal annealing (RTA) and furnace annealing. Distinct PL signatures of confined carriers evidenced formation of Si-nanocrystals (nc-Si) in annealed samples. Analyses of Raman spectra also show presence of nc-Si phase along with amorphous-Si (a-Si) phase in the samples. The strong influence of the annealing parameters on the formation of nc-Si phase suggests broad possibilities in engineering MQW with various optical properties. Interestingly, conversion of the a-Si phase to the nc-Si phase saturates after certain time of furnace annealing. On the other hand, thinner Si layers showed a disproportionately lower crystalline volume fraction. From the obtained results we could assume that an interface strain prevents full crystallization of the Si layers and that the strain is larger for thinner Si layers. The anomalous dependence of nc-Si Raman scattering peak position on deposited layer thickness observed in our experiments also supports the above assumption.  相似文献   

9.
We present a study on amorphous SiO/SiO2 superlattice performed by grazing-incidence small-angle X-ray scattering (GISAXS). Amorphous SiO/SiO2 superlattices were prepared by high-vacuum evaporation of 3 nm thin films of SiO and SiO2 (10 layers each) onto Si(1 0 0) substrate. After the deposition, samples were annealed at 1100 °C for 1 h in vacuum, yielding to Si nanocrystals formation. Using a Guinier approximation, the shape and the size of the crystals were obtained. The size of the growing nanoparticles in the direction perpendicular to the film surface is well controlled by the bilayer thickness. However, their size varies more significantly in the direction parallel to the film surface.  相似文献   

10.
This paper relates a complete study of Si/SiO2 multilayer (ML) structures. First, we suggest an original way of synthesis based on reactive magnetron sputtering of a pure silica target. The photoluminescence spectra of these MLs consist of two Gaussian bands in the visible-near infrared spectral region. The stronger one (I band) is fixed at about 780 nm and probably due to interface states. The weaker one (Q band) is tuneable with the Si sublayer thickness and originates from a radiative recombination within the nanosized Si layers. For this latter band the peak position is a function of the Si sublayer thickness and shows a discontinuity at 30 Å. This corresponds to an Si phase change. For thicknesses above 30 Å, the sublayers are composed of nanocrystalline silicon whereas below 30 Å the sublayers are made of amorphous silicon. We develop a model based on a quantum well to which we have added an interfacial region between Si and SiO2. It is characterised by an interfacial potential of 0.3 eV. This model depicts the simultaneous behaviour of Q and I bands for an Si sublayer thickness below 30 Å.  相似文献   

11.
Results from coincidence Doppler broadening (CDB) measurements on various Si samples and Brazilian quartz having low quartz structure are presented with the aim to give further strong indication of the existence of a low quartz structure, but not of Si divacancies as frequently considered, at the SiO2/Si interface.  相似文献   

12.
We investigate the migration pathway and barrier for B diffusion at SiGe/SiO2 interface through first-principles density functional calculations. Similar to the diffusion mechanism reported for Si/SiO2 interface, a substitutional B, which initially forms a B-self-interstitial complex in SiGe, diffuses to the interface and then to the oxide in form of an interstitial B. At the defect-free interface, where bridging O atoms are inserted to remove interface dangling bonds, it is energetically more favorable for the interstitial B to intervene in the Ge–O bridge bond rather than the Si–O bridge bond at the interface. As a result of the B intervention, interface Ge atoms significantly enhance the stability of B-related defects in the interface region and thereby act as traps for B dopants. At the interface with the Ge–O bridge bond, the overall migration barrier for B diffusion from SiGe to SiO2 is estimated to be about 3.7 eV, much higher than the reported value of about 2.1 eV at Si/SiO2 interface. Our results provide a clue to understanding the experimental observation that B segregation toward the oxide is suppressed in SiGe/SiO2 interface.  相似文献   

13.
The secondary radiation after resonant excitation of F center and its linear polarization P correlated to the polarization of resonant light have been measured for five alkali halides at low temperatures. In KC1, the spectrum of P over the whole Stokes region is divided into three successive regions, the depolarization range at the one-phonon Raman scattering, the near plateau range, and the depolarization range down to vanishing. The former two have common relevance to resonant energy and symmetries of coupled phonons. These relevances are interpreted adopting a configuration coordinate model for 2s- and 2p-like excited states.  相似文献   

14.
We report on continuous-wave laser induced crystallisation processes occurring in Si/SiO2 multiple quantum wells (MQW), prepared by remote plasma enhanced chemical vapour deposition of amorphous Si and SiO2 layers on quartz substrates. The size and the volume fraction of the Si nanocrystals in the layers were estimated employing micro-Raman spectroscopy. It was found that several processes occur in the Si/SiO2 MQW system upon laser treatment, i.e. amorphous to nanocrystalline conversion, Si oxidation and dissolution of the nanocrystals. The speed of these processes depends on laser power density and the wavelength, as well as on the thickness of Si-rich layers. At optimal laser annealing conditions, it was possible to achieve ∼100% crystallinity for 3, 5 and 10 nm thickness of deposited amorphous Si layers. Crystallization induced variation of the light absorption in the layers can explain the complicated process of Si nanocrystals formation during the laser treatment.  相似文献   

15.
Er 3+-doped TiO 2-SiO 2 powders are prepared by the sol-gel method,and they are characterized by high resolution transmission electron microscopy (HR-TEM),X-ray diffraction (XRD) spectra,and Raman spectra of the samples.It is shown that the TiO 2 nanocrystals are surrounded by an SiO 2 glass matrix.The photoluminescence (PL) spectra are recorded at room temperature.A strong green luminescence and less intense red emission are observed in the samples when they are excited at 325 nm.The intensity of the emission,which is related to the defect states,is strongest at the annealing temperature of 800 C.The PL intensity of Er 3+ ions increases with increasing Ti/Si ratio due to energy transfer between nano-TiO 2 particles and Er 3+ ions.  相似文献   

16.
康朝阳  唐军  李利民  闫文盛  徐彭寿  韦世强 《物理学报》2012,61(3):37302-037302
在分子束外延(MBE)设备中,利用直接沉积C原子的方法在覆盖有SiO2的Si衬底(SiO2/Si)上生长石墨烯,并通过Raman光谱和近边X射线吸收精细结构谱等实验技术对不同衬底温度(500℃,600℃,700℃,900℃,1100℃,1200℃)生长的薄膜进行结构表征.实验结果表明,在衬底温度较低时生长的薄膜是无定形碳,在衬底温度高于700℃时薄膜具有石墨烯的特征,而且石墨烯的结晶质量随着衬底温度的升高而改善,但过高的衬底温度会使石墨烯质量降低.衬底温度为1100℃时结晶质量最好.衬底温度较低时C原子活性较低,难以形成有序的C-sp2六方环.而衬底温度过高时(1200℃),衬底表面部分SiO2分解,C原子与表面的Si原子或者O原子结合而阻止石墨烯的形成,并产生表面缺陷导致石墨烯结晶变差.  相似文献   

17.
Novel egg-shell structured monometallic Pd/SiO2 and bimetallic Ca-Pd/SiO2 catalysts were prepared by an impregnation method using porous hollow silica (PHS) as the support and PdCl2 and Ca(NO3)2·4H2O as the precursors. It was found from transmission electron microscope (TEM), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) that Pd was loaded on PHS with a particle size of 5-12 nm in Pd/SiO2 samples and the Pd particle size in Ca-Pd/SiO2 was smaller than that in Pd/SiO2 since Ca could prevent Pd particles from aggregating. X-ray photoelectron spectroscopy (XPS) analyses exhibited that Pd 3d5/2 binding energies of Pd/SiO2 and Ca-Pd/SiO2 were 0.2 and 0.9 eV lower than that of bulk Pd, respectively, as a result of the shift of the electron cloud from Pd to oxygen in Pd/SiO2 and to both oxygen and Ca in Ca-Pd/SiO2. The activity of Ca-Pd/SiO2 egg-shell catalyst for CO hydrogenation and the selectivity to methanol, with a value of 36.50 mmolCO mol−1Pd s−1 and 100%, respectively, were much higher than those of the catalysts prepared with traditional silica gel as the support, owing to the porous core-shell structure of the PHS support.  相似文献   

18.
Y.J. Guo  X.T. Zu  B.Y. Wang  X.D. Jiang  X.D. Yuan  H.B. Lv  S.Z. Xu 《Optik》2009,120(18):1012-1015
Two-layer ZrO2/SiO2 and SiO2/ZrO2 films were deposited on K9 glass substrates by sol–gel dip coating method. X-ray photoelectron spectroscopy (XPS) technique was used to investigate the diffusion of ZrO2/SiO2 and SiO2/ZrO2 films. To explain the difference of diffusion between ZrO2/SiO2 and SiO2/ZrO2 films, porous ratio and surface morphology of monolayer SiO2 and ZrO2 films were analyzed by using ellipsometry and atomic force microscopy (AFM). We found that for the ZrO2/SiO2 films there was a diffusion layer with a certain thickness and the atomic concentrations of Si and Zr changed rapidly; for the SiO2/ZrO2 films, the atomic concentrations of Si and Zr changed relatively slowly, and the ZrO2 layer had diffused through the entire SiO2 layer. The difference of diffusion between ZrO2/SiO2 and SiO2/ZrO2 films was influenced by the microstructure of SiO2 and ZrO2.  相似文献   

19.
We numerically analyzed the thermal characteristic in continuous wave (cw) GalnAsP/InP surface emitting lasers with dielectric multilayer mirrors by using finite element method. From the simulation of temperature distribution in cw devices, we found that MgO/Si multilayer mirror which has a high thermal conductivity is effective for heat sinking; the thermal resistance of device using MgO/Si mirror is nearly half of that using SiO2/Si one, almost independently of their thicknesses. It was also indicated that the optimum design for other structural parameters, especially the thickness of active region, is important to effectively suppress the temperature increase. The minimum threshold current was estimated to be 3 mA under cw condition for the active region diameter of 4 μm and thickness of 0.5 μm.  相似文献   

20.
In this work, the influence of Si/SiO2 interface properties, interface nitridation and remote-plasma-assisted oxidation (RPAO) thickness (<1 nm), on electrical performance and TDDB characteristics of sub-2 nm stacked oxide/nitride gate dielectrics has been investigated using a constant voltage stress (CVS). It is demonstrated that interfacial plasma nitridation improves the breakdown and electrical characteristics. In the case of PMOSFETs stressed in accumulation, interface nitridation suppresses the hole traps at the Si/SiO2 interface evidenced by less negative Vt shifts. Interface nitridation also retards hole tunneling between the gate and drain, resulting in reduced off-state drain leakage. In addition, the RPAO thickness of stacked gate dielectrics shows a profound effect in device performance and TDDB reliability. Also, it is demonstrated that TDDB characteristics are improved for both PMOS and NMOS devices with the 0.6 nm-RPAO layer using Weibull analysis. The maximum operating voltage is projected to be improved by 0.3 V difference for a 10-year lifetime. However, physical breakdown mechanism and effective defect radius during stress appear to be independent of RPAO thickness from the observation of the Weibull slopes. A correlation between trap generation and dielectric thickness changes based on the C-V distortion and oxide thinning model is presented to clarify the trapping behavior in the RPAO and bulk nitride layer during CVS stress.  相似文献   

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