摘要:

A conduction model is developed for the dc electrorheological (ER) response of highly conducting particles (e.g., metal particles) suspended in a weakly conducting oil. The numerical analyses show that a surface film with some conductivity is desired, but not a completely insulating film as previously proposed. Increasing the film conductivity leads to an increase in the ER yield stress. However, too high a conductivity will give an unacceptable level of current density. The film should also have an intermediate thickness. A small thickness increases the possibility of electrical breakdown in the film; too large a thickness decreases the ER effect. Good agreement exists between the yield stress and the current density predicted by our model and those measured. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364123

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Polarization resolved photoluminescence from a cleaved sample edge (edge photoluminescence) is shown to be a useful tool for characterization of complex multiple quantum well InP based structures with wells of different strains. The polarization resolved luminescence resulting from the heavy- and light-hole transitions of In0.51Ga0.49As0.78P0.22tensile and In0.9Ga0.1As0.52P0.48compressive wells are found to match closely with theoretical values, validating assignments applied to the peaks obtained from photoluminescence. Strain distribution is shown to be an important effect when quantum wells of opposite strain are mixed together in the growth structure. The overlap of the transverse-electric (TE) and transverse-magnetic (TM) emissions found from edge photoluminescence on a mixed strain quantum well structure is shown to have an excellent match with the overlap of the TE and TM modes of a laser which uses the same structure in its active region. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364069

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Multiple quantum well InGaAsP/InPp-i-nlaser heterostructures with different barrier thicknesses have been investigated using photoluminescence (PL) and photocurrent (PC) measurements. The observed PL spectrum and peak positions are in good agreement with those obtained from transfer matrix calculations. Comparing the measured quantum well PC with calculated carrier escape rates, the photocurrent changes are found to be governed by the temperature dependence of the electron escape time. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364070

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Piezoreflectance (PzR) and contactless electroreflectance (CER) measurements of an In0.86Ga0.14As0.3P0.7/InP quantum well heterostructure as a function of temperature in the range of 20–300 K have been carried out. A careful analysis of the PzR and CER spectra has led to the identification of various excitonic transitions,mnH(L), between themth conduction band state and thenth heavy (light)-hole band state. The parameters that describe the temperature dependence ofEmnH(L)are evaluated. A detailed study of the temperature variation of excitonic transition energies indicates that the main influence of temperature on quantized transitions is through the temperature dependence of the band gap of the constituent material in the well. The temperature dependence of the linewidth of 11H exciton is evaluated and compared with that of the bulk material. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364071

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have used electric-field-induced Raman scattering to quantitatively assess the effects of carrier screening on the average electric fields in a GaAs-basedp–i–nnanostructure semiconductor under subpicosecond laser photoexcitation. Our experimental results demonstrated that the effects of carrier screening on the average electric field were negligible for a photoexcited electron–hole pair density ofn⩽1015cm−3. As the density of photoexcited carriers increased, we observed a significant decrease of the average electric field. In particular, forn=1018cm−3, a decrease of electric field of about 50&percent; was found. All of these experimental results were explained by ensemble Monte Carlo simulations and very good agreement has been obtained. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364072

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We measured the dielectric constants of strained In0.7Ga0.3AsyP1−y(y=0.2, 0.4, 0.8, 1.0) and lattice-matched 1.32 &mgr;m In1−xGaxAsyP1−ythin films grown on InP substrates by metalorganic chemical vapor deposition. Measurements were performed by phase-modulated spectroscopic ellipsometry in the range of 0.76–4.9 eV. Our data bridge the gap between literature data in the near-infrared region and those in the visible-ultraviolet region. The critical point energies of strained In0.7Ga0.3AsyP1−ywere compared with unstrained counterparts and were found to be shifted in accordance with the theory, which predicts that the compositional shift is compensated. Thus, the critical point energies of strained In1−xGaxAsyP1−ythin films of arbitrary composition can be estimated accurately and, conversely, the composition of strained In1−xGaxAsyP1−ythin films can be estimated by measuring their critical point energies, as for unstrained materials. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364073

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have systematically studied the strain dependence of the free-exciton resonance energies in wurtzite GaN by photoreflectance measurements using well-characterized samples. The experimental data have been analyzed using the appropriate Hamiltonian for the valence bands in wurtzite GaN and determined the values of the crystal field splitting, the spin–orbit splitting, the shear deformation potential constants, and the energy gap in the unstrained crystal. Discussions are given on the strain dependence of the energy gaps, of the effective masses, and of the binding energies for the free-exciton ground states as well as on the valence-band parameters. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364074

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have measured the birefringence(&Dgr;n)of ZnGeP2throughout the 14–500 K temperature range using polarized light interference spectra obtained in transmittance from 0.7 to 12 &mgr;m. It was found that&Dgr;ncontinuously increases with temperature for all wavelengths but that the amount of increase is not constant with temperature as often assumed.&Dgr;nincreases by approximately 0.006 when the temperature changes from 14 to 500 K. The temperature derivative of the birefringence,d(&Dgr;n)/dT, was determined at 50 K increments and its value was found to be quite dependent on the exact temperature range over which it was measured. It increases linearly with temperature, having a coefficient of 3.3×10−8/K. Actuald(&Dgr;n)/dTvalues range from 5×10−6/K at the lowest temperature to 19×10−6/K at the highest. We conclude that the anomalously low phase matching angles observed for second-harmonic generation in ZnGeP2are not associated with errors in birefringence values as previously speculated but instead are most likely due to nonlinear absorption phenomena.

ISSN:0021-8979    

DOI:10.1063/1.364075

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A detailed study of the dependence of the plasma wavelength and free-carrier absorption on the doping concentration in silicon has been made. Two approaches have been used for introducing impurities into Si to achieve high doping concentration. One was the diffusion technique, using spin-on dopants. The plasma wavelength(&lgr;p)of these doped films could be adjusted by controlling the diffusion conditions. The minimum plasma wavelength achieved was 4.8 &mgr;m. In addition, a significant amount of absorption was observed for the wavelength 2 &mgr;m and below. The second approach was doping by ion implantation followed by thermal annealing with a capped layer of doped glass. Implantation with high dosages of B and As followed by high temperature annealing (>1000 °C) resulted in a plasma wavelength that could be controlled between 3.5 and 6 &mgr;m. The high temperature annealing (>1000 °C) that was necessary to activate the dopant atoms and to heal the implantation damage also caused significant redistribution of the dopants. For phosphorous implanted Si, a moderate temperature (800–900 °C) was sufficient to activate most of the phosphorous and to heal the implantation damage. The position of the plasma turn-on wavelength for an implantation dose of 2×1016cm−2of P was at 2.9 &mgr;m. The absorption at 2 &mgr;m was less than 25&percent; and the reflection at 10 &mgr;m was about 85&percent;. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364076

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have studied the effect of various controlled surface oxidation treatments on photoluminescence excitation spectra of porous silicon for various emission energies. The UV excitation spectra of fresh samples were found to be peaked with a monotonic relation between peak excitation energy and emission energy, and to have an onset near 3.3 eV, the direct gap of Si. Aging (ambient oxidation) was found to unevenly affect the excitation spectra, resulting in an effective red shift of the peak center. On the other hand, anodic oxidation or oxidation by exposure of the sample to copper ions in solution caused a blue shift of the excitation spectra. These results are explained in terms of surface condition effects on nonradiative loss sites or on the interquantum dot barriers. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364077

出版商:AIP    

年代:1997

数据来源: AIP