摘要:

The characterization of the crystallinity by Raman image measurements has been made on thin silicon films on insulators, which are deposited by low pressure chemical vapor deposition using silane (SiH4) and disilane (Si2H6) as gas sources and are subsequently thermally annealed. The degree of crystallization by thermal annealing has been quantitatively evaluated by comparing the integrated Raman scattering intensity of the polycrystalline band and the amorphous band. The volume fraction of the crystalline component in samples grown with silane is larger than that grown with disilane for the same annealing time. Raman images of these thin silicon films reveal that the grain size in samples grown with disilane is a few microns, being bigger than that grown with silane. The affect of the source gas on the grain size of crystallites and on the volume fraction of the crystalline component in the films is attributed to the difference in nucleation rate for two kinds of the films during annealing. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359961

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Luminescence spectra and their variation with temperature have been investigated for solid films of poly(methylphenylsilane) and its branched analogs. Introduction of branching points to the polymers enhances the broad luminescence band in the visible region while suppressing the sharp UV luminescence band due to the resonant recombination of the exciton. The intensity of the visible luminescence is observed to keep on increasing with decreasing temperature in contrast with the nearly temperature‐independent intensity of the resonant luminescence. The behavior is interpreted in terms of phonon‐assisted tunneling between luminescence centers and nonradiative ones. ©1995 American Institute of Physics. 

ISSN:0021-8979    

DOI:10.1063/1.359962

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A line‐shape analysis of room temperature photoluminescence (PL) spectra was carried out on Si‐doped GaAs samples grown by molecular beam epitaxy. The electron concentrationnof the samples ranges from 1.0×1017to 4.2×1018cm−3. It was found that the conduction band tail &eegr;cand the Fermi energy &Vegr;fmeasured from the conduction band minimum can be expressed as &eegr;c=2.0×10−8n1/3(eV) and &Vegr;f=−0.074+1.03×10−7n1/3(eV), respectively. The PL peak energy, at which the electron concentration per unit energy in the conduction band is maximum, can also be expressed as 1.426+2.4×10−14n2/3(eV). ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359963

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Picosecond excitation‐probe measurements using a far‐infrared free‐electron laser (CLIO) have revealed large nonlinearities for indium antimonide at 4.7 &mgr;m. A theoretical model is described to determine the cw third‐order nonlinear susceptibility and the interband relaxation time of the semiconductor which were found to be −8.6×10−11m2 V−2and 0.3 ns, respectively. Furthermore, the observation of the associated coherent transient grating effects allows us to obtain a coherence time of the laser system (2.5 ps) and the &khgr;(3)of the transient grating which was found to be −7.2×10−13m2 V−2. The measurements were performed at room temperature on undoped bulk InSb. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359964

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Photoluminescence (PL) and photoreflectance (PR) measurements have been performed to investigate the intermixing behavior of Al and Ga in GaAs/AlAs multiple quantum wells (MQWs) grown by molecular‐beam epitaxy and treated by rapid thermal annealing. These results indicate that the magnitude of the disordering for a GaAs/AlAs MQW increases as the layer thickness increases. When the GaAs/AlAs MQWs with layer thicknesses of 34 A˚ are annealed at 950 °C for 10 s, the GaAs/AlAs MQWs are totally intermixed, resulting in a formation of an Al0.45Ga0.55As alloy. For the intermixed GaAs/AlAs MQWs, PL spectra show dominantly the &Ggr;‐valley direct transition, and PR signals show that the peaks originating from the interband transitions disappear. The observed increases of the full width at half‐maximum (FWHM) in the PL spectra for the annealed GaAs/AlAs MQWs originate from the nonuniformity of the intermixing as a function of depth, and the decrease of FWHM in the PL spectra for the GaAs/AlAs MQWs annealed for longer times is due to the formation of Al0.45Ga0.55As alloys in the GaAs/AlAs MQWs. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359965

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Spectroscopic‐ellipsometry (SE) and thermoreflectance (TR) spectra of GaAs are presented. Measurements are carried out on the same bulk sample in the 1.2–5.6 eV photon‐energy range at room temperature. These spectra are analyzed based on a simplified model of the interband transitions. Results are in satisfactory agreement with the experimental SE and TR data over the entire range of photon energies. The fact definitely links the temperature‐induced change in the dielectric function (TR) to the first derivative of the pseudodielectric function (SE). It is also concluded that the broadening terms cannot be neglected in the analysis of TR spectra. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359966

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The index of Cd1−xMgxTe ternary alloys was measured for the first time by variable‐angle spectroscopic ellipsometry on layers of different concentrations. The ellipsometer’s wide spectral range (0.7–5.6 eV) clearly reveals critical points beyond the gap. Self‐consistency of the permittivity measurements is investigated by Kramers–Kronig analysis. A transition layer is revealed at the top surface of the samples and is taken into account as a rough layer. In the transparent region Sellmeier’s law is applied to describe the index behavior as a function of the wavelength and the magnesium content. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360710

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Amorphous boron carbide (a‐B1−xCx) is believed to have an icosahedron‐based random network. In this paper, vibrational properties ofa‐B1−xCxfilms are studied by IR and Raman spectra, placing particular emphasis on the interpretation of the most prominent 1100‐cm−1band associated with the B–C bond. The 1100‐cm−1band appears in both IR and Raman spectra, and the frequency variation and the intensity as a function of the C content are examined, together with evaluation of the absolute absorption coefficients. Within the framework of the impurity‐induced vibration theory, the 1100‐cm−1band is characterized. The estimation of the force constants by the observed frequencies leads to a conclusion that the vibration can be classified as an extrinsic and preferably a local mode. This vibration is well described as the stretching mode of a localized two‐center bond between the B and C atoms. In this sense, the C atom in amorphous B1−xCxis not regarded as a network constituent. The frequency shift with the C content supports this conclusion. The absorption intensity of this band exhibits large values for the transverse effective charge ofa‐B1−xCx. A numeric estimation shows that most part of the observed transverse effective charge comes from the localized charges of the C impurity. This mechanism of the effective charge is consistent with the above argument of frequency. The intrinsic vibrations of the amorphous boron network based on the icosahedron structure reside over the range from 400 to 1000 cm−1with a small peak at 800 cm−1. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359967

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Charged particles in organic polymer plumes photoablated by ultraviolet lasers are measured with a Faraday cup assembly. In spite of a relatively low F2laser (157 nm) fluence <1 J/cm2, relative charged fragment concentrations measured for polyimide, polytetrafluoroethylene, and polyethyleneterephthalate targets are ≳10−3. Charged particle concentrations in the ablation plumes generated by an F2laser with polyethyleneterephthalate and polyimide targets are always higher than those in KrF laser (248 nm) ablation plumes at the same specific laser energy deposited on the target. Charged fragments have also higher velocities in the F2laser ablation plumes. An exponential increase in the charged fragment concentration with increasing laser fluence suggests that the ions are mainly produced through electron‐neutral collisions in the hot material core close to the target surface. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359968

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Experiments have been performed to measure, in real time, the formation of AlO molecules from laser‐ablated Al atoms in oxygen gas and plasma environments. The Al atom plume is generated by focusing a KrF laser (4 J/cm2) on Al metal targets or polycrystalline Al2O3(alumina) ceramic. AlO molecule formation has been characterized by emission spectroscopy at 464.82 and 484.22 nm molecular bandheads. Time‐integrated and time‐resolved optical emissions have been measured of laser‐ablated Al atoms interacting with oxygen or argon neutral‐gas versus plasma backgrounds generated by a high‐voltage capacitive discharge. Results indicate that gas/plasma‐phase reactions occur between laser‐ablated Al atoms and oxygen. Optimal enhancement of AlO optical emission is measured in oxygen plasmas at about 200 mTorr fill pressure. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359969

出版商:AIP    

年代:1995

数据来源: AIP