摘要:

Optical and electrical properties of the LiBO2–LiF composite thin films prepared by thermal evaporation have been studied for their use as ion conductors in solid‐state electrochromic (EC) systems. All the LiBO2–LiF films exhibited a high degree of optical transmission (over 90%) and the best lithium ion conductivity attainable was about 8×10−7S cm−1, a value considerably higher than that for the ionic conductivity of LiBO2. A typical activation energy of 0.545 eV was found for the composite film. The films obtained thus have a good potential for use as ion conductors in EC devices. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359624

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The morphology of Ge layers, a few micrometers thick, grown by chemical‐vapor deposition on GaAs substrates, is very sensitive to the growth conditions. The evolution of the intensity of the dynamicinsitureflectometry reveals different growth features. We present here an analysis of the basic elements from which it is possible to deduce important physical parameters of the Ge layers: the shape of the growth defects, their density, the optical index of the homogeneous layer, and the effective index of the rough layer. The respective contributions of the scattered and refracted intensities to the measured intensity are described semiempirically. Typical experimental curves and their corresponding time‐dependent growth rate, optical index, and morphology are given. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359625

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The time evolution of the charge carrier density, ionized donor density and space‐charge field under a sinusoidal light pattern have been calculated by solving numerically the nonlinear differential equations for a photorefractive material (such as BSO). The time evolution for optical erasure starting from the steady‐state solution has also been obtained. Arbitrary modulation depths have been considered for two relevant cases: pure diffussion and under an applied dc electric field of 5 kV/cm. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359626

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The results of a systematic photoluminescence study of ZnGa2O4:Mn powder phosphor are reported. At room temperature this phosphor exhibits bright green luminescence with a spectral peak at 2.46 eV and Commission International de l’Eclairage chromaticity coordinates ofx=0.073 andy=0.696. At low temperatures the luminescence was found to consist of three components assigned to the4T1–6A1inner transition of the 3delectrons of Mn2+ions located on three different sites of the host crystal. Selective excitation and lifetime measurements were used to investigate the assignment of these features. The photoluminescence lifetime showed a single exponential decay of about 4 ms and atT=1.6 K an optical‐phonon‐related fine structure [Ephonon=(8.2±0.2) meV] of the main photoluminescence line was observed. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359627

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We report the dependence on the excitation power and temperature of the photoluminescence emission from a quaternary Ga0.75In0.25As0.04Sb0.96/Al0.22Ga0.78As02Sb0.98strained multiple‐ quantum‐well structure grown by molecular‐beam epitaxy. Sharp exciton resonances are observed up to room temperature and have been attributed to localized excitons for temperatures ≤80–100 K and to free excitons at higher temperatures up to room temperature by a comparative study with temperature‐dependent absorption spectroscopy. We conclude that the dominant luminescence quenching mechanism in this quaternary system is mainly due to the trapped excitons thermalizing from the localized regions below 100 K, and the thermal carrier activation from the first electron and heavy‐hole subbands to the second electron and heavy‐hole subbands at higher temperatures. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359628

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Synchrotron radiation soft x‐ray photoemission spectroscopy was used to investigate the development of the electronic structure at the CdS/Cu2−xSe and CdS/In6Se7heterojunction interfaces. Cu2−xSe and In6Se7layers were deposited on GaAs (100) by physical vapor deposition from Cu2Se and In2Se3sources. CdS overlayers were then depositedinsitu, at room temperature, in steps on these layers. Photoemission measurements were acquired after each growth to observe changes in the valence‐band electronic structure and changes in the In4dand Cd4dcore lines. The results were used to correlate the interfacial chemistry with the electronic structure and to directly determine the CdS/Cu2−xSe and CdS/In6Se7heterojunction valence‐band discontinuities and the consequent heterojunction band diagrams. These results are compared to the valence‐band offset (&Dgr;Ev) for the CdS/CuInSe2heterojunction interface.

ISSN:0021-8979    

DOI:10.1063/1.359629

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Thermal diffusivity for carbon fiber composites was measured using different fiber types and polymer matrices. Photothermal testing was performed in the various directions parallel and perpendicular to the carbon fiber axis by different photothermal configurations. By focusing the laser beam with a spherical lens, local inhomogeneities of the composite surface in the range of 10 &mgr;m are distinguished. When focusing is done with the aid of a cylindrical lens an averaging over larger scales of the photothermal deflected signal takes place. The results for various carbon fiber materials are discussed in terms of thermal diffusion lengths and thermal diffusivity values. It is shown that the thermal photodeflection method is suitable for measuring anisotropy in oriented carbon fiber composites. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359630

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Highly conductive phosphorus‐dopedn‐type hydrogenated microcrystalline silicon (&mgr;c‐Si:H) films have been prepared by the usual (13.56 MHz) radio‐frequency glow discharge of silane (SiH4), phosphine (PH3), and hydrogen (H2) in an ultrahigh‐vacuum deposition system. The highest conductivity of the films obtained in this study is 100 S cm−1after optimizing the hydrogen dilution ratio, chamber pressure, substrate temperature, and doping concentration of phosphorus. The formation of microcrystallinity in the material has been studied by transmission electron microscopy, x‐ray‐diffraction studies, and Raman spectroscopy. The volume fraction of microcrystallinity in these amorphous‐microcrystalline mixed‐phase materials has been estimated from Raman spectra. Sizes of the crystallites and volume fraction of microcrystallinity vary with hydrogen dilution, chamber pressure, and substrate temperature. The variations in the properties with deposition parameters have been explained in terms of the growth kinetics. Then‐type &mgr;c‐Si:H thin film, thus developed, has been applied in the first cell of a double‐junction amorphous silicon solar cell. The preparedp‐i‐n–p‐i‐nstacked cell employing then‐type &mgr;c‐Si:H film has exhibited appreciable improvement in open‐circuit voltage, fill factor, and efficiency compared to the one with amorphousnlayer in the innern–pcontact. Degradation of the cells prepared with and without &mgr;c‐nlayer has been studied. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359631

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

2H–AlN(0001) layers have been grown on Si(111) by reactive magnetron sputtering from an Al target in Ar+N2gas mixtures at temperaturesTs=400–900 °C. Variations in reactive gas consumption, target voltage, and current–voltage characteristics versus nitrogen partial pressure were used to determine deposition parameters required to yield stoichiometric AlN with growth rates ≥2 &mgr;m h−1. High‐resolution cross‐sectional transmission electron microscopy (XTEM) analyses of films grown at 900 °C showed that the initial 6–8 monolayers were (111)‐oriented cubic 3C before transforming to the (0001)‐oriented 2H polytype. The epitaxial relationship was found by XTEM and x‐ray diffraction (XRD) to be 2H–AlN(0001)//3C–AlN(111)//Si(111) with 2H–AlN[12¯10]//3C–AlN[110]//Si[110]. High‐resolution XRD &ohgr;−2&THgr; and &ohgr; rocking curve widths for films grown atTs=900 °C were 70 and 500 arc sec, respectively, the lowest values yet reported. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359632

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Insituscanning tunneling microscopy (STM) was employed to examine the electrochemical etching process of ann‐Si(111) electrode in dilute NH4F solutions under potential control. Time‐dependent STM images have revealed prominent effects of microscopic structures of Si on the rate of its dissolution. Multiple hydrogen‐terminated Si atoms at the kink and step sites were eroded more rapidly than the monohydride Si step. This presumably resulted from the difference in reactivity of these hydrogen‐terminated Si species. It is demonstrated that the density of kinks plays a main role in controlling the etching rate of Si. In the absence of kinks, not only the monohydride but also the dihydride steps were found to be stable. The etching rate of the monohydride step is substantially increased from a negligible value to 15 nm/min by the introduction of kink sites. The average etching rate for a dihydride step was 32 nm/min. Overall, the difference in the reactivity guides the dissolution of Si in a layer‐by‐layer fashion. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359633

出版商:AIP    

年代:1995

数据来源: AIP