摘要:

Plates of Al–Si alloy were anodized in a sulfuric acid solution. This treatment provides aSi–Al2O3coating growing at a rate of 0.14 &mgr;m/min. The Si particles had sizes between 1 and 10 &mgr;m, as seen by scanning electron microscopy. Optical measurements showed a continuous decrease of reflectance with increasing film thickness. The reflectance of theSi–Al2O3coated aluminum could be understood from a four flux radiative transfer theory. In order to explain our measurements, it was found necessary to include a free-carrier term in the dielectric permittivity of Si. The free carriers are probably due to doping with Al. Hence, the relaxation time of the free carriers is determined by scattering from the charged Al impurities. ©1997 American Institute of Physics. 

ISSN:0021-8979    

DOI:10.1063/1.365668

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We present photoluminescence (PL) and infrared absorption on sets of porous silicon with peak energy ranging from 1.5 to 1.9 eV prepared at different anodization current density. The effects of the as-grown samples under several different treatments have been investigated. Quite surprisingly, the PL peak positions of all the samples studied shift toward 1.7 eV upon the introduction of more oxygen by annealing in a low-temperatureH2environment then exposing to the air. This behavior indicates that the 1.7 eV emission plays a unique role in the PL spectra of porous silicon. However, samples rinsed in water show only blueshift. From our measurements, we conclude that PL emission in porous silicon contains two components. One is the above-mentioned 1.7 eV peak, which can be correlated to the absorption of O–Si–H bonds. The other component of PL is shown to be sensitive to the strength of the Si–O–Si bond related absorption. Based on the previous reports and the results shown here, a possible PL mechanism in porous silicon is emerging. We propose that PL originates from quantum confinement effect for samples with peak energy lower than 1.7 eV. For samples with PL peak larger than 1.7 eV, the PL results from the fact that after generated in the nanocrystalline silicon by photon pumping, the carriers relax into the surface states and then make a radiative recombination. We studied the evolution of the PL spectra under laser illumination and found that the anomalous behavior in the evolution process can also be explained with our model. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365669

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

X-ray induced photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy, and electron microprobe analysis (EMA) were used to study semi-insulating polycrystalline silicon layers obtained by chemical vapor deposition fromSiH4andN2Ogases. A mean “bulk” oxygen concentration determined by EMA ranged from 16 to 50 at. &percent;. Photoelectron spectra excited by Mg K&agr;and Al K&agr;radiation were used to find surface composition and bonding information of as-received layers. Beneath the native oxide with a stoichiometry close to theSiO2,there is a heterogeneous material consisting of silicon (Si–Si) and silicon oxide (Si–O) regions. A drop in the Si2ppeak position differences with the mean bulk oxygen concentration indicates a differential charging of the silicon islands surrounded by a silicon oxide phase. A spectral band of an asymmetric Si–O–Si stretching vibration mode around1030 cm−1was used to characterize the samples. An assumption that the samples were a homogeneousa-SiOxphase leads to a mean oxygen content much higher than that determined by the EMA technique. On the other hand, oxygen concentration deduced from the number of (Si–O) bonds, calculated by the normalized integrated absorption intensity, were very close to the results of EMA. This leads us to the conclusion that the samples consist of two phases,a-SiOrand Si. The values of the refractive index obtained by the spectrophotometric method from reflectance spectra and the results of XPS measurements strongly support the two-phase model. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365670

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Single-crystalline hexagonal GaN (&agr;-GaN) films have been grown on (0001) sapphire substrates by metalorganic chemical vapor deposition at 1040 °C. The complex dielectric functions,&egr;(E)=&egr;1(E)+i&egr;2(E),of the epitaxial films have been measured by spectroscopic ellipsometry (SE) forE⊥cin the region between 1.5 and 5.0 eV at room temperature. Previously published ultraviolet SE spectra of &agr;-GaN are examined by considering the effects of surface roughness using an analysis based on an effective medium model.Ex situatomic force microscopy is used to assess independently surface flatness. By mathematically removing the effects of surface roughness, the most reliable&egr;(E)values for &agr;-GaN are presented in the 1.25–10 eV photon–energy range. Theoretical dispersion analysis suggests that theE0structure could be characterized by a three-dimensionalM0critical point and theE1&agr;(&agr;=A,B,C)structures by two-dimensionalM1critical points. To facilitate design of various optoelectronic devices, dielectric-function-related optical constants, such as the complex refractive index, absorption coefficient, and normal-incidence reflectivity of &agr;-GaN are also presented. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365671

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Laser ablation from a binary target into a diluted gas background is studied by means of a Monte Carlo simulation. The influence of the ambient gas on the spatial and mean energy distribution of particles deposited at the distant detector is considered. Thermalization of the particles, the random scattering effect and the backscattering of particles were observed. Considerable modification of the deposited film thickness profiles due to collisions of the ablated particles with the ambient gas is shown. The increase of the ambient gas pressure was found to affect the stoichiometry distribution of deposited and backscattered particles. The study is of a particular interest for the development of the thin film growing technique known as pulsed laser deposition. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365672

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

In order to investigate the gas phase condensation in the pulsed-laser deposition (PLD) process, an ultraviolet (uv) laser light scattering system has been developed and applied for the diagnostics of laser-ablated plumes during the pulsed-laser deposition process of high-Tcthin film fabrications. Time-of-flight measurements were carried out from 1 &mgr;s to 1 s after ablation. Rayleigh-scattered signals from the condensing particles have clearly shown that the condensation occurs in the gas phase under typical PLD conditions. The condensation was noticeable at a large delay time of 10 ms after ablation. At a shorter delay time of less than 500 &mgr;s, laser-induced fluorescence signals from molecules, which were accidentally excited by the uv laser, were also observed. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366283

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The lateral oxidation of buriedAlxGa1−xAslayers with high Al content(x=0.8–1)is investigated, using an oxidation process in a wetN2+H2Oambient at 370–450 °C. The oxidation is clearly selective and significantly affected by process temperature, material composition,AlxGa1−xAslayer thickness, and the geometry of the oxidized structures. An asymptotic oxide growth with constant activation energies for the reactive process and for the transport mechanism is observed. The experimental oxidation behavior coincides well with a model of self-blocking pores. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365758

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We report results from molecular dynamics simulations of the etching of a Si surface by energetic Cl atoms(15 eV⩽E⩽200 eV).We find that the energy dependence of the Si yield (number of Si atoms desorbed per incident Cl ion) is in reasonable agreement with recent experiments and with previous simulations performed up to 50 eV. We also investigate the variation of the Si yield with the impact angle of incidence, the stoichiometry of the desorbed material, and the effect of a thermal background Cl flux to the surface in the presence of an ion flux at 50 eV. Surface roughening due to etching was observed and the calculated rms roughness is in reasonable agreement with experiments. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365674

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Two-dimensional temperature maps of reactive gas layers were produced using pulsed laser Rayleigh scattering thermometry. The measurements were made in conditions of diamond film chemical vapor deposition (CVD) using a thermal inductively coupled plasma. In these conditions, the reactive gas layer is typically a few millimeters thick and the temperature drops across the layer from 4000 K at the free stream boundary to about 1200 K at the substrate. The reactive layer exhibits strong chemical nonequilibrium. Rayleigh scattering was induced using a pulsed laser sheet at 532 nm wavelength. The scattered radiation was detected and calibrated with an intensified charge coupled device camera. Temperature maps and axial profiles obtained under parametric variation of the gas flow conditions demonstrate how the technique can be employed to measure the reactive layer thickness and its radial distribution across the substrate. The results demonstrate that imaging Rayleigh scattering thermometry can be employed as a nonintrusive diagnostic tool to obtain useful experimental information pertinent to the gas phase chemistry in diamond CVD under conditions of extremely large temperature gradients. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365687

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The chemisorption of bis(trimethylsilyl)methane (BTM,CH2[Si(CH3)3]2) and dodecamethylcyclohexasilane (DCS,Si6(CH3)12) on clean Si(100) surfaces has been studied by C1score-level and valence-band photoemission spectroscopy. Our model for the deposition of carbon by BTM involves decomposition into a–CH2Si(CH3)3surface moiety for room-temperature adsorption, which further decomposes upon annealing to 550 °C to form a surface terminated primarily byCHxunits. DCS deposits almost three times as much C on the surface as BTM. The data are consistent with DCS undergoing a ring opening and bonding to the surface as polydimethylsilane chains. Annealing both adsorbates to 950 °C causes a large decrease in the C1ssignal due to the fact that Si segregates to the surface at temperatures above 900 °C. The valence-band photoemission of Si(100) dosed with DCS at 950 °C is in good agreement with that of &bgr;-SiC, whereas the analogous BTM spectrum deviates significantly.

ISSN:0021-8979    

DOI:10.1063/1.365759

出版商:AIP    

年代:1997

数据来源: AIP