摘要:

The reflection, transmission, and absorption coefficients are derived for long-wavelength electromagnetic radiation propagating through a medium that exhibits a Gaussian conductivity. It is shown that, under certain circumstances, this applies to the ionosphere. The effects of different peak conductivities and Gaussian widths are examined, and a useful form for calculating transmission and reflection coefficients is presented. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364063

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The motion of tapered fiber probes was studied both theoretically and experimentally. A continuum-mechanical model, including both the intrinsic and the external loss, is proposed to account for the vibration dynamics of the probe. The intrinsic loss was found to be the dominant damping factor experimentally. Analytical solutions based on a realistic probe geometry were obtained for the model in the presence of intrinsic loss. The results are compared with the measured overall motions of the tapered probe. The calculations agree well with the experimental results. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364016

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The structural features of the Sr2Nd1−xCaxCu2O5+yF1+&dgr;(0⩽x⩽1) oxyfluoride system have been investigated by electron diffraction and high resolution electron microscopy. The short-range-order (SRO) state has been observed in the Sr2Nd0.5Ca0.5Cu2O5+yF1+&dgr; oxyfluoride (Tc≈70 K). This kind of SRO structure can be understood in terms of the ordering of insertion of fluorine and/or oxygen atoms located between the SrO(F) double layers. The most probable ordering scheme is proposed. The effects of Ca content on this kind of SRO state as well as other locally ordered states have also been investigated.©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364017

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

In this study, dislocation motions in GaN-based materials and devices were quantitatively estimated in order to determine why GaN-based light-emitting diodes have remarkable reliability and longevity in spite of extremely high dislocation density. The dislocation velocity of GaN-based materials was calculated by estimating the activation energy of dislocation, and comparing it with that of GaAs, which are typically used for light-emitting devices. It was estimated that the dislocation mobility of GaN-related materials was lower than that of GaAs by a factor of approximately 10−10–10−16, at room temperature. Furthermore, dislocation velocity under current injection became about 10−20times lower than that of GaAs, under the assumption that the dislocations in GaN-related materials do not act as nonradiative recombination centers. The possibility of degradation under high current densities and high temperature, as would be found in GaN-based laser diodes, is also discussed. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364018

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We demonstrate that the depth distribution of defects in MeV implantedn-type andp-type crystalline Si is severely affected by the impurity content of the material. Silicon samples with different concentrations of dopants (P or B) and intrinsic contaminants (i.e., C and O) were implanted with 1 or 2 MeV He ions to fluences in the range 2.5×108–1×1013/cm2. Using deep-level transient spectroscopy and spreading resistance measurements, we have identified the defects and determined their concentration and depth distribution. It is found that less than 4&percent; of the defects generated by the beam escape recombination and are stored in electrically active, room temperature stable defect clusters, such as divacancies and carbon–oxygen pairs. When the concentration of these defects is much smaller than the doping level, their profile mirrors the initial defect distribution, as calculated by transport of ions in matter (TRIM), a Monte Carlo code. In particular, the profile presents a maximum at the same depth predicted byTRIMand a width which is strongly dependent on the impurity content of the substrate. Indeed this width can be as large as 2 &mgr;m when implants are performed on a lightly doped, pure epitaxial substrate and returns to the value predicted byTRIM(∼0.5 &mgr;m) upon increasing the concentration of dopants and intrinsic contaminants which act as traps for the diffusing point defects. The broadening of the concentration profiles is however shown to be unavoidable at high implantation fluences when most of the traps are already full and unable to interrupt the free migration of newly generated defects. Finally, by comparing defect distributions inn-type andp-type samples we have detected the spatial separation between vacancy-type and interstitial-type defects, resulting from the ion momentum transfer. The observed phenomena are explained in terms of a trap limited diffusion of the defects generated by the beam. These effects are only observable for a light ion such as He since direct defect clustering within the diluted collision cascades is expected to be significantly inhibited. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364019

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Infrared absorption measurements were made of the localized vibrational modes due to defects produced in Czochralski-grown Si material after irradiation with fast neutrons and subsequent thermal treatments. The investigation was focused, in particular, on three satellite bands in the region of the A center, located at 839, 833 and 824 cm−1respectively, the annealing behavior of which was carefully monitored. Correlation of our results with previous infrared, electron paramagnetic resonance and positron annihilation studies favors attributing these bands to theV2O,V3O2and V2O2defects respectively. In addition, semiempirical calculations were carried out for the vibrational frequencies of these defects, and the predicted values are in agreement with the above assignments. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364020

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Silica glasses were repeatedly densified by multiple shock reverberations in stainless-steel capsules. The limit of increase in density was about 2.47 Mg/m3after the first shock loading. Further increase in density was observed after duplicate shock loading, but limited at about 2.55 Mg/m3. Triplicate shock loading was not so effective for the increase in density. The Raman spectra of recovered silica glasses had characteristics of densified silica glass with much higher density. The remarkable one was the enhancement of the line at 605 cm−1called the D2line, which was one of two narrow lines peculiar to the Raman spectrum of silica glass. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364021

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Transient enhanced diffusion (TED) of boron in silica after low energy boron implantation and annealing was investigated using boron-doping superlattices (DSLs) grown by low temperature molecular beam epitaxy. Boron ions were implanted at 5, 10, 20, and 40 keV at a constant dose of 2×1014/cm2. Subsequent annealing was performed at 750 °C for times of 3 min, 15 min, and 2 h in a nitrogen ambient. The broadening of the boron spikes was measured by secondary ion mass spectroscopy and simulated. Boron diffusivity enhancement was quantified as a function of implant energy. Transmission electron microscopy results show that ⟨311⟩ defects are only seen for implant energies ⩾10 keV at this dose and that the density increases with energy. DSL studies indicate the point defect concentration in the background decays much slower when ⟨311⟩ defects are present. These results imply there are at least two sources of TED for boron implants (B-I): short time component that decays rapidly consistent with nonvisible B-I pairs and a longer time component consistent with interstitial release from the ⟨311⟩ defects. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364022

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The effects of strain on tin diffusion in GaAs were studied by using laser Raman and photoluminescence spectroscopies. It was found that an increase of compressive strain on GaAs causes an increase of the carrier concentration while a decrease of compressive strain or an increase of tensile strain causes a decrease of the carrier concentration at the surface of GaAs. The results are due to the decrease of the diffusion coefficient of tin in GaAs with compressive strain and the increase of it with tensile strain. Photoluminescence data showed that the peak due to Ga antisite defects increased with increase of compressive stress. This indicates a decrease of Ga vacancy concentration from the equilibrium concentration in an unstressed sample. On the other hand, photoluminescence data from the tensile stressed sample showed an increase of Ga vacancy concentration from the equilibrium concentration in an unstressed sample. Thus, the change of the diffusion coefficient with strain seems to be related to Ga vacancy. It was also found that the diffusion coefficient decreased exponentially with compressive strain and increased exponentially with tensile strain with the result that the activation energy of tin diffusion in GaAs varied linearly with strain. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364023

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The diffusion of implanted zinc in GaAs is studied and modeled for annealing temperatures of 625 through 850 °C. Secondary ion mass spectrometry data for the annealed profiles are presented. The substitutional interstitial diffusion (SID) mechanism is used to explain how the deviation of the local gallium interstitial concentration from its equilibrium value regulates the Zn diffusion. We are able to simulate both the box shaped profiles resulting from high temperature anneals and the kink-and-tail profiles resulting from lower temperature anneals. The simulation results have allowed us to determine Arrhenius relations for: the intrinsic diffusion coefficient for implanted Zn,DZnint=0.6075 exp(−3.21 eV/kBT) cm2 s−1; the equilibrium Ga interstitial concentration,CIGa*=7.98×1030 exp(−3.47 eV/kBT)cm−3; and the Ga interstitial diffusion coefficient,DIGa=0.4384 exp(−2.14 eV/kBT)cm2 s−1. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364024

出版商:AIP    

年代:1997

数据来源: AIP