摘要:

Ultralow‐power, high‐resolution, pulsed‐laser photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopies were carried out in molecular‐beam‐epitaxial GaAs/AlxGa1−xAs multi‐quantum‐well structures at 5 K. Fine structures were observed for the first time in the PLE spectra, both in the heavy‐hole and light‐hole excitonic regions. Most of the fine structures are considered to arise from monolayer fluctuations in the thicknesses of the GaAs wells. Dramatic changes in the line shapes and the peak positions of the PL and PLE spectra were observed by applying selective PL detection and excitation spectroscopic techniques.

ISSN:0021-8979    

DOI:10.1063/1.337268

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A hole diffusion length in liquid‐encapsulated‐czochralski (LEC) GaAs monocrystals (Si‐doped,n&bartil;1015–1016cm−3) in the range (0.4–3.0) 10−4cm, has been determined by photon and electron bombardment through semitransparent Au or Cr Schottky electrodes. A minority‐carrier lieftime in the range (0.3–9.7) 10−9s was estimated. Schottky barrier diodes with abrupt junctions giving optimum electrical characteristics were prepared. The absorption length of the examined samples was evaluated by optical transmission measurements. The diffusion length investigation, which was carried out by the steady‐state surface photovoltage (SPV) and the scanning electron microscope electron‐beam‐induced current (SEM‐EBIC) techniques, has been related to the spectral quantum efficiency of Schottky diodes. SPV and EBIC techniques are emphasized as complementary methods for the investigation of bulk photoelectronic properties.

ISSN:0021-8979    

DOI:10.1063/1.337269

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Schottky‐barrier diodes have been fabricated by evaporation of Pt on Si substrates followed by annealing at 500 °C to yield PtSi. Then V and Al were evaporated. The amount of oxygen intentionally incorporated in the V film during deposition was varied and the resulting effect on the diffusion barrier action of the vanadium film has been studied byI‐VandC‐Vmeasurements of the diodes and by backscattering spectrometry of simultaneously prepared test samples. It is found that for V films with low oxygen concentrations annealing in the range 400–600 °C leads to the formation of VAl3and subsequent barrier height change. For vanadium films containing 50‐at. % oxygen there is no observable reaction between V and Al and the barrier height is preserved for annealing between 400 and 600 °C.

ISSN:0021-8979    

DOI:10.1063/1.337775

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The magnetic wave interactions on a thin film with interfaces having the profile of a periodic array of rectangular grooves are investigated. The film is assumed to be magnetized uniformly normal to the midplane. The technique is based on a transmission line model which is valid even for large relative depths of variation of the film thickness. When specialized to small relative depths of variation of the film thickness, the spectral characteristics of the power reflection coefficient determined by this large‐amplitude theory are in good agreement with those predicted by the existing small‐amplitude theories. The present large‐amplitude theory shows that the small‐amplitude theory gives the maximum of the power reflection coefficient reasonably correctly but overestimates the center frequency, the error increasing with the increasing values of the relative depth of variation of the film thickness. The investigation of the characteristics of the first two band gaps with the help of the present large‐amplitude theory reveals interesting features in the behavior of the band gaps as the relative depth of variation of the film thickness becomes large.

ISSN:0021-8979    

DOI:10.1063/1.337270

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The magnetic field splitting and strain splitting of the emission lines in the 1.5040–1.5110 eV range in GaAs are reported. In the Voigt configuration the lines show doublet splittings in applied magnetic fields. In combined magnetic and strain fields four lines are observed in this configuration. All of the lines show a similar splitting. The splittings agree with what would be expected for shallow donor‐acceptor pair centers in a zinc‐blende structure.

ISSN:0021-8979    

DOI:10.1063/1.337271

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

We introduce and discuss a fractal model for dielectric breakdown which exhibits a breakdown voltage and a region of stable prebreakdown structures. The model provides a unifying picture covering homogeneous space charge injection, treelike structures, and filamentary breakdown. A simple qualitative relation between the global form of the pattern and two simple physical parameters is found. The model illustrates the intricate relationship between local stochastic and global deterministic aspects of dielectric instablilities.

ISSN:0021-8979    

DOI:10.1063/1.337219

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

We report the first time‐resolved x‐ray absorption measurements on pulsed laser irradiated Si in the photon energy range from 90 to 300 eV, at irradiation energy densities up to 4 J/cm2, and at several delay times between irradiation pulse and x‐ray probe pulse. The absorption spectra recorded at a delay time of 12 ns can be classified in three categories. Below ≊0.17 J/cm2only thermal damping of extended x‐ray absorption fine‐structure (EXAFS) oscillations is observed. Between ≊0.17 J/cm2and ≊1 J/cm2annealing takes place. Several changes are observed, among which a ≊7‐eVLII,IIIedge shifts towards higher energy, while theLIedge remains approximately at the same position. This edge shift behavior is explained by a largely reduced 3sdensity of states of the conduction band. This supports the idea that pulsed laser molten Si has a metalliclike structure. Thermal damping in this region is so strong that EXAFS oscillations are no longer visible. This is consistent with a lattice temperature above or equal to the melting temperature of Si. Above 1 J/cm2, the damage region, further edge shifts and the development of several peaks are observed. Clear cooling effects are visible at long delay times (60 ns) between irradiation and x‐ray probe pulse. Cooling on this time scale can only be explained by evaporation of Si.

ISSN:0021-8979    

DOI:10.1063/1.337220

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The thermal viscoplastic stresses and the dislocation densities in silicon ribbon are computed for an axially changing thermal profile by using an iterative finite difference method. A material constitutive equation (Haasen–Sumino model) which involves an internal variable (mobile dislocation density) is used. The results are interpreted as showing that there is a maximum width of silicon ribbon that can be grown when viscoplasticity and dislocations are considered. This maximum width limitation does not exist if the material behavior is elastic.

ISSN:0021-8979    

DOI:10.1063/1.337221

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Both the steady‐state and transient solute (impurity) concentrations at the surface of a film during its deposition are calculated as a function of deposition rate, temperature, diffusivity, bulk film solute concentration, and segregation energy. The steady‐state solute concentration at the surface is found to increase upon increasing either the solute diffusivity or the magnitude of the (negative) segregation energy, or upon decreasing the deposition rate. The transient concentration profile at the start of deposition relaxes toward the steady‐state profile as 1/t. Implications of the present results for film growth mechanisms and methods to control the degree of segregation via manipulation of deposition parameters are discussed.

ISSN:0021-8979    

DOI:10.1063/1.337222

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

This paper presents a study on drawing condition dependences of optical absorption at 630 nm and nonbridging oxygen hole centers (NBOHCs) in optical fibers drawn from low‐OH‐content synthetic silica glass. The intensity of the 630‐nm absorption is proportional to the NBOHC concentration, and the value of the oscillator strength for the NBOHC is 4.2×10−4, which nearly equals the theoretical values. These results confirm that the 630‐nm absorption is due to the NBOHCs in low‐OH‐content silica glass. Furthermore, the 630‐nm absorption increases with increasing drawing tension. This drawing tension dependence is explained by applying kinetics of the stress‐induced crack growth in metal to the formation of the NBOHCs in the drawing process.

ISSN:0021-8979    

DOI:10.1063/1.337785

出版商:AIP    

年代:1986

数据来源: AIP