摘要:

To understand the mechanisms for elastic precursor decay in pure ⟨100⟩ lithium fluoride (LiF) crystals under shock loading we have examined the role of large dislocation densities produced near the crystal surfaces by sample preparation. After unsuccessfully trying various methods to produce flat and undamaged samples, we chose to harden the surfaces by inward diffusion of magnesium fluoride (MgF2). A combination of heat treatments and other procedures was developed to ensure hardened or doped surfaces with a maximum depth of 600 &mgr;m and an undoped interior. Sample characterization was carried out using dislocation etch pit, hardness, and electron microprobe measurements. A 0.24‐mm sample, with MgF2completely diffused through, gave a 16.7‐kbar precursor amplitude. A 2.93‐mm sample with a front diffusion layer of 0.14–0.39 mm and a back diffusion layer of 0.00–0.32 mm and undoped interior gave a precursor amplitude of 2.1 kbar. These experiments indicate that the surface damage layer does not control precursor decay in pure LiF crystals.

ISSN:0003-6951    

DOI:10.1063/1.96906

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The temperature stability of metal (W, WRe, Co, Cr)‐carbon multilayers has been studied using x‐ray diffraction (&thgr;–2&thgr; and Debye–Scherrer) and electron microscopy. The results show that in all cases a crystallization occurs in the temperature range 650–750 °C. As a consequence of this crystallization, the layered structure is destroyed, the surface of the film becomes rough, and the x‐ray reflectivity is considerably reduced. These results imply that efficient cooling or new multilayer structures will have to be developed for use at high temperatures or under high x‐ray incident flux.

ISSN:0003-6951    

DOI:10.1063/1.96907

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Gold‐silicon interfaces have been studied under ultrahigh vacuum conditions. The interface growth, its characterization by Auger electron spectroscopy, and its irradiation by low‐energy (1–3 keV) electrons have all been carried outinsitu. We have estimated the adhesion of the gold layer by the peeling test. The adhesion is good when Au is deposited on a clean Si substrate and poor when a native oxide (thickness ∼10–15 A˚) is present at the interface. We show that the electron irradiation decomposes the oxide partially and this produces a drastic increase of the adhesion. The oxide decomposition is not thermally induced and is attributed to electronic effects. We suggest that the formation of Au–Si bonds at the interface is at the origin of the adhesion enhancement.

ISSN:0003-6951    

DOI:10.1063/1.96908

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

We report the room‐temperature pulsed operation of GaAs/(Al,Ga)As double heterojunction laser structures grown directly on (100)Si. Current thresholds of as low as 170 mA in 10‐&mgr;m‐wide stripe lasers have been achieved at 280 K. Power output as high as 44 mW per facet was also obtained. Assuming no current spreading, the corresponding current threshold density is 6.9 kA/cm2. Slope efficiencies andT0values of 0.18 W/A and 165 K, respectively, have also been obtained. These results are directly attributable to the reduction of dislocations by choosing growth conditions and step density on the surface.

ISSN:0003-6951    

DOI:10.1063/1.96909

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

We report the first simultaneous measurements of the photoluminescence yield and of the basic electronic properties (density of states, position of the Fermi level) of InP surfaces subjected to various treatments under ultrahigh vacuum conditions. The surface densities of states located near the band edges are found to govern the surface recombination process. Annealing under As pressure which moves these densities out of the band gap is shown to yield a surface with low surface recombination, in agreeement with this framework.

ISSN:0003-6951    

DOI:10.1063/1.96910

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Using the technique of hot‐electron spectroscopy we have measured the change in hot‐electron spectra with transit region width enabling us to obtain a dynamic picture of injected hot‐electron cooling inn+GaAs. All features in the spectra have been identified and ‘‘ballistic’’ transport has been observed for samples having narrow transit region widths (<850 A˚) while near diffusive transport has been observed for samples having wide transit region widths (>1700 A˚). With increasing transit region width, rather than the electron distribution shiftingenmasseto lower energies, electrons are removed from the initial injected peak and scattered to lower energies close to the Fermi energy. This process of electron cooling is dramatically illustrated by measuring the magnetic field dependence of the hot‐electron spectra.

ISSN:0003-6951    

DOI:10.1063/1.96911

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Ann‐channel double heterostructure optoelectronic switch has been demonstrated. As in the case of thep‐channel device, there is a high impedance state without light emission and a low impedance state with strong spontaneous emission. The states are changed by optical or electrical signals and a digital optical gain of 14 is observed. The switching voltage is higher and the holding current is lower than in thep‐channel case.

ISSN:0003-6951    

DOI:10.1063/1.96912

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The solubilities of iron in samples treated with various oxygen precipitation treatments were compared. The solubility of iron was reduced by almost two orders of magnitude in samples containing low‐temperature oxygen precipitates. It is suggested that a new phase forms, probably an oxygen‐metal rich compound that is more stable than the FeSi2silicide. This study suggests dramatic improvements for the efficiency of gettering processes.

ISSN:0003-6951    

DOI:10.1063/1.96913

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

We present experimental results which clearly separate the various physical mechanisms which cause persistent photoconductivity in GaAs/AlxGa1−xAs heterojunctions. For high Al mole fraction the major contribution is from the donor‐relatedDXcenter. This contribution is eliminated by reducing the Al mole fractionx, but we observe a ‘‘residual’’ effect forx≲0.2. We show that this is due to the persistent photovoltage developed between channel and semi‐insulating substrate. Charge trapping in the epitaxial GaAs buffer layer contributes negligibly, contrary to the assumptions of other workers. This is demonstrated by fabricating modulation‐doped field‐effect transistors of low Al mole fraction on conductive substrates. In these devices persistent photoconductivity is eliminated as long as the substrate (back gate) potential is fixed with respect to the channel.

ISSN:0003-6951    

DOI:10.1063/1.97028

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The high‐pressure liquid encapsulated Czochralski growth of indium lattice‐hardened GaAs, from 3 kg melts, has resulted in low‐dislocation, large‐diameter crystals which exhibit thermally stable, semi‐insulating properties. Post‐growth boule annealing is found to be an effective stress‐relief treatment, which assures high wafer yields and extremely uniform electrical properties. Observed reductions in dislocation density for mid 1019cm−3In‐doped GaAs substrates indicate an apparent 28‐fold increase in the critically resolved shear stress of this material over undoped GaAs near the melting point. Polished substrates obtained from these crystals exhibit very little subsurface damage, approaching high‐quality silicon wafers in this respect.

ISSN:0003-6951    

DOI:10.1063/1.96914

出版商:AIP    

年代:1986

数据来源: AIP