摘要:

The properties ofp‐njunctions fabricated by Si compensation in the AlxGa1−xAs alloy system have been investigated. The radiative emission is shown to occur via centers substantially removed from the band edges. At 300°K,E0‐hvpvaries from 0.12 eV at a bandgap energy of 1.49 eV to a maximum of 0.33 eV whenE0=1.86 eV. A deep acceptor level due to a Si complex is believed to be involved. As a result internal reabsorption of the emitted light is small compared to Zn‐doped junctions where the emission is closer to the absorption edge. External efficiencies of 1%–2% on uncoated, edge emission diodes are observed in the near‐infrared portion of the spectrum (8600 Å), at current densities as low as 5 A/cm2. The highest efficiency obtained is 7% at 8800 Å with an encapsulated diode. The radiative efficiency at 300°K is shown to vary with the bandgap energy (i.e., separation between direct and indirect conduction band minima). ForEg=2 eV (when the indirect band is lower than the direct one by about 0.1 eV), the efficiency is reduced to 0.025% at a peak emission wavelength of 7000 Å. However, at 77°K, the efficiency varies by only a factor of ∼5 betweenEg=1.49 eV andEg=2 eV. The difference between 300° and 77°K is explained by free‐electron‐to‐acceptor‐recombination at 300°K, which changes to donor‐to‐acceptor recombination at 77°K. In comparison with other methods of diode preparation by vapor phase epitaxy or diffusion, (in AlxGa1−xAs or GaAs‐P) the present devices offer the convenience of a one step growth process in simple apparatus. The low internal reabsorption further simplifies the diode fabrication process because high efficiency devices are obtained even with edge emission structures. Thus it is possible to have large surfaces available for Ohmic contact which results in minimal diode series resistance.

ISSN:0021-8979    

DOI:10.1063/1.1657966

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Electroluminescent diodes were prepared by the simultaneous diffusion of boron and aluminum at 2150° to 2250°C into nitrogen‐doped,n‐type 6HSiC crystals. These diodes exhibit a typical brightness of 50 ft·L (170 nit) at a current density of 5 A/cm2for temperatures of 25° to above 200°C. The results of various measurements on these diodes are presented and the anomalous nature of the diffusion is discussed.

ISSN:0021-8979    

DOI:10.1063/1.1657967

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Anisotropy aging and stabilization effects have been investigated in vapor‐deposited zero‐magnetostrictive Permalloy films by annealing either in a rotating magnetic field or in an easy direction field. Two major components in the anisotropy relaxation were observed. Amounts of the two components are comparable in fresh films. By stabilization annealing at 300°C for 35 h, the fraction of the anisotropy affected by the faster component can be made less than17of the total initial anisotropy, during which time the relaxation frequency of the slower component gradually decreases from about 10−4sec−1to about 10−6sec−1. The fast component is suggested to be related to high‐diffusivity paths in films while reorientation of the ordered atomic pairs as a result of the bulk diffusion process can account for the slow component. However, the vacancy concentration is found to be far in excess of the thermal equilibrium value in fresh films, leading to marked increases in the initial diffusion rates compared with bulk Permalloy values. It is found that the vacancy rate‐of‐change process follows the chemical rate equation of order 2, which suggests the formation of divacancies. The change‐of‐slope method is introduced for determination of the activation energy for atomic movement involved in the reorientation process of atom pairs, giving a value of 1.6 eV which is in reasonable agreement with estimates of this quantity from bulk data.

ISSN:0021-8979    

DOI:10.1063/1.1657968

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Anomalous behavior has been observed in the electrical resistivity of gadolinium single crystals in the region 210°–250°K. The results are correlated with the rapid deviation of the magnetic moment from the hexagonal axis in this temperature range.

ISSN:0021-8979    

DOI:10.1063/1.1657969

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The low‐temperature (1.4° to 4.2°K) specific heat, the ferromagnetic Curie temperature, and the magnetic moment of Ni&sngbnd;Cu solid solutions were measured near the composition where ferromagnetism terminates. The anomaly in the specific heat cannot be accounted for by thebT3lnTterm expected from electron‐paramagnon interaction, but it can be interpreted as a magnetic cluster contribution independent of temperature from 1.4° to 4.2°K. Another magnetic contribution is included in the term of the specific heat linear in temperature. Whether the maximum in the linear term at 50–54 at.% Cu should be attributed to this magnetic contribution or to the (enhanced) electronic specific heat is uncertain. For alloys near the critical composition the Curie temperature, as determined by methods based on high field data, is distinctly higher than that measured at low fields.

ISSN:0021-8979    

DOI:10.1063/1.1657970

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

A precise determination of the temperature dependence of the zero external field F19NMR frequency in the antiferromagnet FeF2has been made over the temperature range from 4.2°K to 0.99966TN. Ferrous fluoride, unlike the previously studied antiferromagnet MnF2, has a large single ion magnetic anisotropy. The present data, which were taken on a high‐quality single crystal with one millidegree temperature control and measurement techniques, were carefully least‐squares fitted to the equation&ngr;19(T)/&ngr;19(0)=D(1−T/TN)&bgr;over ranges &thgr; <T/TN<0.99966. For &thgr;=0.995, it is found that &bgr;=0.333±0.009,D=1.428±0.067,TN=78.373±0.005, while for &thgr;=0.971, &bgr;=0.320±0.001,D=1.341±0.005,TN=78.367±0.001. The present data, which demonstrate the need for precise measurements and analysis over small ranges nearTN, are at variance with the wider‐range power law fits reported recently by Wertheimet al.A Kouvel‐Fisher plot of the present data shows that the apparent value of &bgr; drops rather rapidly for &thgr;<0.95. This behavior is distinctly different from MnF2, where the apparent value of &bgr; varies more slowly. Although no analysis of the data below the critical region has yet been made, its accuracy should prove helpful for comparison with spin‐wave interaction theories.

ISSN:0021-8979    

DOI:10.1063/1.1657971

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The single‐crystal elastic constants of Ni3Al were determined by a rod resonance technique. Their values and standard deviations at 25°C in units of 10−12m2/N ares11=9.27±0.15,s44=8.25±0.27, ands12=−3.19±0.50.

ISSN:0021-8979    

DOI:10.1063/1.1657972

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Preyield dislocation motion and multiplication were studied in large‐grained polycrystalline OFHC copper by the etch‐pit technique. Specimens were loaded in compression and dislocation arrangements were observed in both the stressed and unstressed conditions. The dislocation loops generated by the first few active sources on both primary and secondary slip systems generally traversed the entire cross section of the grain. The observations were consistent with the idea that jog density is an important factor in determining the mobility of a dislocation segment. The external surface was found to be a preferential site for dislocation multiplication even when grown in segments, where they cut the surface, were immobile, and stress concentrations were carefully avoided. It is suggested that the rapid increase in length per unit volume of moving dislocation line that is associated with macroscopic yield requires motion of dislocation segments of high jog density.

ISSN:0021-8979    

DOI:10.1063/1.1657973

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The rate‐dependent constitutive relation developed by Taylor, which considers dislocation motion only in glide directions and on glide planes for which the shear stress is maximum, is extended to include dislocation motion in all glide directions on all glide planes. The theory requires that grain orientation be random, that expanding dislocation loops be rectangular, and that the velocity of edge dislocations be much greater than the velocity of screw dislocations. The velocity of screw dislocations is assumed to be given byvs=vmexp (‐B/&tgr;), where &tgr; is the applied shear stress,Bis a constant, andvmis the elastic shear wave velocity. On the basis of this theory, elastic wave attenuation in Armco iron is calculated and compared with the experimental data of Taylor and Rice. It is found that the mobile dislocation density necessary for the theoretical calculation to agree with experimental data is five times greater than that obtained by Taylor on the basis of the simpler theory. Likewise, for a given shear stress, it is found that the dislocation velocity is greater than that determined previously. This indicates that the results obtained on the basis of the simpler theory may significantly underestimate the velocity of individual dislocations as well as the mobile dislocation density.

ISSN:0021-8979    

DOI:10.1063/1.1657974

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

A sound‐wave hologram was constructed by sampling the acoustic field with a microphone and simulating a reference wave electronically. The frequency of the sound wave was chosen as 18 kHz. The optical reconstruction of image from the obtained hologram was carried out using the 6328 Å laser light. A zero‐order image and higher‐order images were reconstructed from a grating‐like sound‐wave hologram produced by the scanning of the microphone.

ISSN:0021-8979    

DOI:10.1063/1.1657975

出版商:AIP    

年代:1969

数据来源: AIP