摘要:

We report pseudodielectric function ⟨&egr;⟩ data for AlxGa1−xAs alloys of target compositionsx=0.00–0.80 in steps of 0.10 grown by liquid‐phase epitaxy and measured by spectroellipsometry. Cleaning procedures that produce abrupt interfaces between the technologically relevant alloysx≤0.5 and the ambient are described. The ⟨&egr;2⟩ data are corrected near the fundamental direct absorption edge by a Kramers–Kronig analysis of the ⟨&egr;1⟩ data to circumvent a limitation of the rotating‐analyzer ellipsometric technique. The results and the associated pseudooptical functions ⟨n⟩, ⟨R⟩, and ⟨&agr;⟩ are listed in tabular form. Accurate values of theE0andE1threshold energies are determined from these spectra by Fourier methods. From these values, and from similar values for a GaAs‐capped AlAs sample grown by organometallic chemical vapor deposition, the dependencies of theE0andE1interband critical point energies on nominal composition are obtained. Cubic polynomial representations of these dependences are determined to allow nominal Al fractions to be calculated analytically from optical threshold data. The systematic behavior of ⟨&egr;1⟩ at 1.5 eV and of theE2peak in ⟨&egr;2⟩ near 5 eV show that scatter in these data is less than 1% of the peak values of the spectra forx≤0.5. Forx≥0.6 the peak data appear to show systematic discrepancies indicating that chemical cleaning cannot completely remove surface overlayers on high‐Al‐content samples. Optical measurements for a sample withx=0.9 also reveal the oxidation of high‐Al samples proceeds irregularly and not along a uniform spatial front. Interpolation procedures to obtain approximate representations of dielectric function spectra at compositions other than those measured are discussed, and suggestions for improving accuracy in future optical measurements on these and related materials are also given.

ISSN:0021-8979    

DOI:10.1063/1.337426

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The low‐temperature photoluminescence of undoped GaxIn1−xAs layers, lattice matched to InP, grown by liquid‐phase epitaxy and molecular‐beam epitaxy has been studied. In this work, we focus mainly on the origin of the line broadening of the two main emissions (excitonic and donor‐acceptor pair transitions) observed. We find that, as it has been recently shown in GaxAl1−xAs, the dominant broadening mechanism is alloy broadening, due to random cation distribution. This model gives linewidths of the bound exciton and the donor‐acceptor pair transitions based on compositional fluctuations within the crystal volumes which are characteristic of the two transitions. Calculated linewidths agree rather well with experimental results, thus demonstrating that alloy broadening leads also in GaxIn1−xAs to a quantitative understanding of the low‐temperature photoluminescence spectra. Careful analysis of the donor‐acceptor pair band yields acceptor activation energies of 15, 22, and 25 meV which are attributed to C, Zn, and Si, respectively.

ISSN:0021-8979    

DOI:10.1063/1.337427

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Optical properties of ZnSe–ZnTe strained‐layer superlattice (SLS) grown on InP substrates were evaluated by photoluminescence. The luminescence peak intensity and position were affected by the photoexcitation intensity. The line shape was also affected by the growth temperature. The peak position was shifted by tailoring the structure of the superlattice, but it did not correlate exactly with previously reported theoretical values. We have reconsidered their data, and a better result on theoretical calulation was achieved. The luminescence color changed in the visible region from green to red. This SLS could be a new material for optoelectronic devices.

ISSN:0021-8979    

DOI:10.1063/1.337428

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Multiple angle of incidence spectroscopic ellipsometric data show that implantation of 150‐keV molybdenum ions into polished molybdenum laser mirrors causes microscopic surface smoothing, and that most of the microscopic roughness is removed by a fluence of 5×1015cm−2. Implantation of Au at 1 MeV significantly increases the microscopic roughness, and also changes the bulk optical properties. 3‐MeV Ni ion implantation causes only small changes in the surface and bulk properties. A dielectric film, probably a hydrocarbon, is found to condense on the mirrors in a laboratory atmosphere.

ISSN:0021-8979    

DOI:10.1063/1.337429

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Transmission electron microscopy (TEM) observations are reported on defects induced in polycrystalline silicon ribbon during the burn‐off of the carbon support and the diffusion process. Ribbon‐shaped silicon crystals are characterized by a high carbon and oxygen content at their solubility limits. TEM investigations show that SiO2is precipitated as either alpha or beta quartz on the dislocation cores during annealing in O2atmosphere.

ISSN:0021-8979    

DOI:10.1063/1.337430

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Ultraviolet (UV) absorption spectroscopy has been used to monitor the concentrations of gas‐phase reactants participating in the growth of InGaAsP alloys by hydride vapor‐phase epitaxy. Room‐temperature absorption spectra for PH3, AsH3, and HCl as well as high‐temperature (700°C) spectra of InCl, GaCl, PH3,P2, P4, As2, and As4are presented. For the group V species, the UV absorption bands of the hydride, dimer, and tetramer exhibit considerable overlap, but can still be used to determine the approximate concentration of each species. GaCl and InCl exhibit extremely intense, sharp absorption bands at 248 and 267 nm, respectively. This technique has been used to study the effect of PH3pyrolysis on InP growth, and to monitor In/Ga ratio for metal transport from an alloy source. This technique can be implemented on reactor systems without reactor design changes and without disturbing the thermal profile by using ‘‘light pipes’’ to probe concentrations of reactive species during growth.

ISSN:0021-8979    

DOI:10.1063/1.337431

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The generation of slip dislocations in BF2ion‐implanted, 100‐mm‐diam silicon wafers during rapid thermal annealing is investigated. Whole wafer x‐ray topography shows that annealing at 1150 °C causes slip to initiate randomly at positions of maximum resolved stress at the wafer edges and over scribe marks made on the back surface prior to annealing. Lowering the annealing temperature by 20 °C, which corresponds to decreasing the silicon yield stress by less than 106dyn cm−2, prevents slip from occurring and allows sufficient removal of implantation‐induced defects from which junction diodes with good current‐voltage characteristics are fabricated.

ISSN:0021-8979    

DOI:10.1063/1.337377

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The structural features of three different graphite fibers were studied via small‐ and wide‐angle x‐ray techniques. The experimental evidence is consistent with a sheath/core fiber morphology. Graphitization, degree of orientation, crystallite size, and microporosity were analyzed. Samples included low (AS4) and high (HMS) modulus poly(acrylonitrile) (PAN) and melt‐spun pitch‐based (VSB‐16) fibers. By wide‐angle x‐ray diffraction (WAXD) VSB‐16 was found to have the highest degree of graphitization, the highest degree of orientation, and the largest crystallite regions, and AS4 the poorest graphitized structure. The void system in these graphite fibers was investigated by small‐angle x‐ray scattering (SAXS). SAXS from glycerin‐soaked fibers indicates the scattering at very small angles (2&thgr;<10 mrad) is dominated by total reflection of x rays at the fiber surface. The pores in HMS and VSB‐16 fibers are inaccessible to glycerin and the pores in AS4 fiber are partially accessible. The pores in PAN‐based HMS and AS4 fibers are of needlelike shape and those in VSB‐16 are ellipsoidal. The porosity is 12.6%, 8.4%, and 4.5% in HMS, AS4, and VSB‐16 fibers, respectively. Deviations from Porod’s law were observed at large angles and attributed to scattering from fractal aggregates of carbon atoms in the graphite crystallites and/or fractal boundaries of pores. The fractal dimension of the aggregates is 2.3±0.1, 2.8±0.2, and 3.0±0.2 for AS4, HMS, and VSB‐16 fibers, respectively. Speculations about the fractal nature of aggregation may stimulate some new insight to the graphitization process, paracrystallinity, and the strength of graphite fibers.

ISSN:0021-8979    

DOI:10.1063/1.337378

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Polycrystalline gallium arsenide films of 10‐&mgr;m thickness deposited on tungsten/graphite substrates by the reaction between gallium, hydrogen chloride, and arsine have been used for the fabrication of thin‐film homojunction solar cells. The major problem associated with polycrystalline gallium arsenide thin‐film cells is the grain‐boundary shunting effect. In order to prepare solar cells with conversion efficiency higher than 10%, gallium arsenide films with large grains are necessary. Unlike gallium arsenide, germanium films can be easily recrystallized to enhance the grain size. Thin‐film gallium arsenide solar cells of thep+/nconfiguration with an AM1 efficiency of about 10% have been prepared using recrystallized germanium and large‐grain germanium substrates.

ISSN:0021-8979    

DOI:10.1063/1.337379

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The optimum emitter surface dopant concentration (Ns) in passivated silicon solar cells is found for different base resistivities with the help of a computer model. The model takes into account not only the band‐gap narrowing, Auger and surface recombination effects on the dark saturation current, but it also considers the variation of series resistance as the impurity concentration changes. The results obtained with the model show different behavior for passivated and nonpassivated solar cells. The open‐circuit voltage and the conversion efficiency of nonpassivated solar cells is almost independent of the surface impurity concentration when this parameter is greater than 2×1019cm−3. On the other hand, for passivated solar cells the optimum value is in the range 2.5×1019cm−3≤Ns<5×1019cm−3for typical base resistivities. Furthermore, it is confirmed that even whenNsis high (Ns>1×1020cm−3) there is an advantage in efficiency of passivated solar cells over those which have a high recombination at the surface. However, in order to increase the efficiency appreciablyNshas to be optimized. The model also gives a procedure to optimize the grid design simultaneously with the surface concentration, assuming the other parameters are optimum.

ISSN:0021-8979    

DOI:10.1063/1.337380

出版商:AIP    

年代:1986

数据来源: AIP