摘要:

The effect of a large static electric field on the Faraday and Voigt free‐carrier magneto‐optical effects in semiconductors is calculated for a parabolic band, for acoustic scattering, and for both high and low frequencies and low losses. It is shown that the electric field produces a larger relative change in the Voigt effect than in the Faraday, and that sizable effects may occur in all cases. Only the effect of the electric field on heating up the charge carrier distribution is considered, specifically directional effects being neglected. Comparison is made with experiments on indium antimonide.

ISSN:0021-8979    

DOI:10.1063/1.1658264

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Theoretical curves of the voltage dependence of cathodoluminescence have been obtained for the case where the intensity of cathodoluminescence varies superlinearly with the net carrier generation rate. Calculations are based on numerical integration of the distribution of excess carriers assuming a Guassian approximation to the distribution of excitation with depth. The theoretical curves make possible the measurement of diffusion lengths using the method of voltage dependence of cathodoluminescence in specimens where the intensity of cathodoluminescence is not linearly proportional to the specimen current (e.g.,p‐type GaAs). Experimental results with accelerating voltages of 5–50 kV using a defocused electron beam and selected area technique indicate values of electron diffusion length inp‐type GaAs ranging from 3.2 &mgr; at low carrier concentration (6.9×1016cm−3) to 0.6 &mgr; at high carrier concentration (3.76×1019cm−3).

ISSN:0021-8979    

DOI:10.1063/1.1658265

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The relation between infrared absorption and mobility in gallium arsenide has been examined. The absorption theory of Haga and Kimura was used, as suggested by Vakulenko and Lisitsa, to calculate a theoretical drift mobility vs concentration curve forn‐type gallium arsenide at 300°K. For concentrations above 1×1017cm−3, this curve agrees well with that obtained from the Ehrenreich variational calculation. The Haga‐Kimura theory was used also to predict that at temperatures between 77° and 300°K and concentrations above 1×1017cm−3, the free‐carrier absorption coefficient &agr; in the far infrared (50–500 &mgr;m) takes the simple classical form &agr; ∝N&lgr;2/&mgr;, whereNis the carrier concentration, &lgr; the wavelength, and &mgr; the drift mobility. This result suggests that far infrared absorption data may be used to directly calculate drift mobilities.

ISSN:0021-8979    

DOI:10.1063/1.1658266

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

A model is presented showing that there is a previously unrecognized source of stress in epitaxially grown heterojunction structures, specifically caused by a set of inclined dislocations formed by misfit dislocations which turn upwards at the heterojunction. This stress is indirectly related to the lattice mismatch at the heterojunction. For small lattice mismatch, the inclined dislocations are in an ordered array and cause the layer to bend upon removal from the substrate. For large lattice mismatch, the inclined dislocations are random so that there are only localized stresses and no net bending stress. A series of heterojunctions of GaAs1−xPxvapor grown onto GaAs were prepared, and the GaAs1−xPxconstant‐composition layers were removed from the substrate. The bending of the layers observed and the dislocation morphologies revealed in the layers by transmission electron microscopy, demonstrate the validity of the above model. In GaAs0.8P0.2grown on GaAs, the stress due to lattice mismatch exceeds that due to differential thermal contraction.

ISSN:0021-8979    

DOI:10.1063/1.1658267

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

A transition from a 2×1 to an 8 structure on the ultrahigh‐vacuum‐cleaved germanium {111} face during heat treatment below 350°C makes germanium particularly well suited as a material for investigating a possible correlation between surface states and surface structure. Individual studies of either the electrical or structural properties of this surface have been made over a number of years, but the present experiment was designed to make both the structural and electrical measurements ``simultaneously'' on the same surface. In the present experiment both surface state density as calculated from surface conductivity and dc‐field effect, and surface structure as characterized by symmetry and spot intensities of the LEED pattern were determined at 30°C as a function of heat treatment over the temperature range 30° to 300°C. The structural changes are accompanied by parallel changes in surface conductivity and field effect mobility. It is concluded that at cleaved germanium surfaces the surface states are essentially determined by the two‐dimensional surface structure rather than domain boundaries or surface defects. A model which correlates different surface state distributions with the 2×1 and the 8 germanium superstructures allows the description of the present results. This is the first time that changes in surface state distributions have been directly correlated with changes in the two‐dimensional surface structure.

ISSN:0021-8979    

DOI:10.1063/1.1658268

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The electrical output which is obtained from an anodized aluminum layer during shock‐wave loading has been studied as a function of shock stress, sample area, shock propagation direction, and temperature history. The dependence of the electrical response on these variables is shown to be consistent with an electret‐like behavior of the anodized layers. A sample macroscopic model based on this behavior is used to predict the features of the electric output.

ISSN:0021-8979    

DOI:10.1063/1.1658269

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The equations of motion of a one‐dimensional lattice of mass points connected by nonlinear springs are set forth and compared with the equations of the corresponding continuum. A permanent regime for the damped lattice is obtained by series approximation and shown to agree with that of the continuum. A higher approximation leads to a permanent regime profile for the undamped lattice which oscillates steadily after shock arrival. This is shown to be in qualitative accord with the results of numerical integrations of the transient problem. However, comparison of periods of steady oscillation with those obtained in the transient problem indicate that the series approximation to the permanent regime is quantitatively unsatisfactory, though qualitatively correct. Scaling of the problem with a parameteru1&agr; is noted, whereu1is steady particle velocity behind the shock and &agr; is a parameter of nonlinearity.

ISSN:0021-8979    

DOI:10.1063/1.1658270

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Velocities for one‐dimensional release waves in 2024‐T4 aluminum alloy have been obtained between 30 and 132 kbar. Stress‐time records were obtained with piezoresistive manganin gauges. The release wave clearly showed the existence of two release systems. The leading edge of the release wave was 27% faster than the bulk sound velocity calculated from the ideal fluid model. The second release system was identified by a change in slope of the release wave profile. The peak velocity of this release system did correspond more closely to the hydrodynamic bulk sound velocity. These results imply elastic behavior of aluminum at high pressure. The shape of the release wave, however, cannot be fitted by a perfect elastic‐plastic model, thus pointing out the need of a more elaborate description.

ISSN:0021-8979    

DOI:10.1063/1.1658271

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Data are presented from a study conducted to examine the shock‐loading behavior of a sintered porous tungsten with a density of 12.64 g/cm3(corresponding to 65.3% of the density of solid tungsten). The experiments were performed by using a gas gun and high explosives. Hugoniot data obtained in the stress range between about 12 kbar and 1 Mbar indicate that compression of the porous material to a fully compacted state is essentially complete at 50 kbar. Above this level, a predicted Hugoniot, calculated from the Hugoniot of solid tungsten by using the Mie‐Gru¨neisen equation of state, agrees well with experimental data. Below 50 kbar the Hugoniot of the porous tungsten deviates from the predicted Hugoniot increasingly with decreasing stress. Propagated wave profiles at lower stresses are characterized by two precursor waves, the faster being a low‐level wave (∼0.2 kbar) traveling at about sonic velocity in the porous tungsten (∼3.04 mm/&mgr;sec). The slower precursor has an amplitude of 2.73 kbar and travels at 2.02 mm/&mgr;sec. The behavior of this porous tungsten is analogous to the behavior of sintered porous copper previously studied.

ISSN:0021-8979    

DOI:10.1063/1.1658272

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Release adiabats and Hugoniot curves centered at shock states can be readily determined by impacting a projectile disk onto a stationary reverberation disk made of a linear elastic material of known shock properties. The reverberation disk may have a free back surface or may be backed by a buffer disk made of the specimen or some other material. The reverberation disk is very thin compared to the thicknesses of the other disks so that many wave reverberations occur in it during the experiment. Depending on the impedance of the reverberation disk relative to the other disks, each reverberation successively unloads, or loads, the projectile disk, thus establishing points on a release adiabat or on recentered Hugoniot curves of the specimen material. The technique is particularly valuable for measurements on compressible nonlinear materials, and it generates a large amount of information in a single experiment. Experiments have been performed with X‐cut quartz, Lucalox, and 60° orientation sapphire reverberation disks which illustrate the technique, and results are presented for an epoxy resin and a porous tuff.

ISSN:0021-8979    

DOI:10.1063/1.1658273

出版商:AIP    

年代:1969

数据来源: AIP