Compositional and structural evolution of the titanium dioxide formation by thermal oxidationSu Wei-Feng(苏卫锋) a) , Gnaser Hubert b)c) , Fan Yong-Liang(樊永良) a) , Jiang Zui-Min(蒋最敏) a) , and Le Yong-Kang(乐永康) a)c) †
The Reflection High Energy Electron Diffraction (RHEED) intensity oscillations under different angles of incidence and azimuths during Si(111) molecular beam epitaxy have been studied. The phase of intensity oscillation and initial transient response change dramatically with the angles of incidencl if the observation is carried out along [112] azimuthal direction, but vary little when observed along [011] azimuth. From the measurement results of RHEED specular beam rocking curve, we believe that, the characteristics of RHEED intensity oscillation as a function of electron diffraction condition, indicate the existence of two different seattering processes: coherently elastic diffraction beam oscillation and inelastic or diffuse scattering beam oscillation. This can be explained only by the electron multiple scattering mechanism. The origin of initial transient is also discussed.
Electroluminescence (EL) from Sibased organic microcavity has firstly been reported in the literature. The microcavity is made up of the central active multilayers sandwiched between a silver film and a porous silicon Bragg reflector (PSDBR), formed by electrochemical etching of p+Si substrate in the electrolyte of HF: C2H5OH:H2O. The central active multilayers consist of Al (1 nm) / LiF (05 nm) / Alq3 / Alq3: DCJTB / NPB / CuPc / ITO / SiO2. The reflectivity (relative to an Al mirror) of the PSDBR is up to 99%, and the stopband is about 160 nm wide. Resonant cavity mode appears as a tip in the reflectivity spectrum of the Sibased organic multilayer films, indicating that the Sibased organic multilayer structure is indeed a microcavity. The peak widths of the EL spetra are greatly reduced from 70 nm to 12 nm as compared with those measured from noncavity structures. Note that the EL emission from the cavity devices is singlemode, and the offresonant optical modes are highly suppressed. Moreover, an increase of a factor of about 4 of the resonant peak intensity is observed. In addition, the currentbrightnessvoltage characteristics and the effect of parameters on the lifetime of the cavity devices are also discussed. The present technique for obtaining enhanced EL emission from Sibased organic microcavity may also be another novel effective method for realizing allSibased photonic devices and optoelectronics device integration.
GexSi1-x/Si strained-layer superlattices were grown on Si(lOO) substrates under different temperatures by molecular beam epitaxy. Methods such as reflection high energy electron diffraction, X-ray double crystal diffraction, Rutherford back scattering, transmission electron microscopy and Raman scattering have been applied to study the growth and characteristics of the GexSi1-x/Si superlattices. The result show that the optimum growth temperature are different for superlattices with different composition, the smaller the x the higher the growth temperature, and vice versa. For x = 0.1-0.6, the GexSi1-x/Si superlattices with flat interfaces, good crystal perfection and uniform periodicity can be obtained with growth temperature in the range of 400-600℃.
The admittance spectroscopy technique has been used to study the hole confinement in Si/Si1-xGex/Si and boron highly doped superthin Si quantum wells. Based on the carrier thermal emission medel of the carriers in the well, the value of activation energy derived from the admittance spectra was considered as the distance from the position of the heavy hole ground state in the well to the top of it . For Si/Si1-xGex/Si quantum wells we found the value of activation energy increased with increasing annealing time at 800℃. The phenomena could be explained the annealing-induced interdiffusion of Si and Ge, the interface broadening, the weakening of quantum confinement, the decrease of the position of the heavy hole ground state, and so the increase of the activation energy. At the annealing temperature of 900℃, we only see the decrease of the value of activation energy with increasing annealing time. For boron highly doped superthin Si quantum wells due to quantum confinement effect, we observed the activation energy are different for samples with the same doping density but different well widths.
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