摘要:

The physics of the growth mechanisms, characterization of epitaxial structures and device properties of GaAs and other compound semiconductors on Si are reviewed in this paper. The nontrivial problems associated with the heteroepitaxial growth schemes and methods that are generally applied in the growth of lattice mismatched and polar on nonpolar material systems are described in detail. The properties of devices fabricated in GaAs and other compound semiconductors grown on Si substrates are discussed in comparison with those grown on GaAs substrates. The advantages of GaAs and other compound semiconductors on Si, namely, the low cost, superior mechanical strength, and thermal conductivity, increased wafer area, and the possibility of monolithic integration of electronic and optical devices are also discussed.

ISSN:0021-8979    

DOI:10.1063/1.346284

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The transport mean free path, or transport cross section, is tabulated for the elastic scattering of electrons and positrons in solid matter by means of a correction factortcapplied to the result of a simple screened Rutherford cross section. The correction factor table is based on differential cross‐section calculations using a combination of partial‐wave analysis (PWA), the Wentzel–Kramers–Brillouin approximation, and the Born approximation, and covers kinetic energies from 100 eV to 20 MeV. Results at low energies are compared with PWA calculations of higher accuracy. Nuclear size effects are discussed but not explicitly included. Applications are discussed.

ISSN:0021-8979    

DOI:10.1063/1.346399

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Calculations of Mott elastic scattering cross section of electrons for most elements of the periodic table up to element number 94 in the energy range 20 eV–20 keV have been performed. The Dirac equation transformed to a first‐order differential equation was solved numerically. The influence of the choice of atomic potential on the scattering factor was studied in comparison to a simple muffin‐tin approximation of the atomic potential in solids. The application of calculated cross sections to a conventional Monte Carlo model for electron scattering using modified Bethe equation is described and results concerning the electron backscattering for different atomic potentials are compared.

ISSN:0021-8979    

DOI:10.1063/1.346400

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Phase locking of a vircator array driven by a relativistic magnetron in a pure master–slave configuration has been achieved. A single high voltage pulse drives the relativistic magnetron and the vircator array in series. Phase locking occurs for ∼40 ns. The time required to lock is &bartil;10 ns. the peak array power is &bartil;1 GW. The injection ratio, &rgr;, and allowable frequency difference, &Dgr;f, relationship required for phase locking is examined. The results suggest that the Adler’s inequality, &rgr;≳(Q/&Dgr;f)f, is a necessary, but not sufficient condition to predict phase locking. A hybrid configuration in which the driven vircators are also mutually connected together has also been attempted. Phase locking is observed with better phase stability than in the pure master–slave configuration.

ISSN:0021-8979    

DOI:10.1063/1.346401

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A theoretical model is presented to describe the time‐harmonic electromagnetic induction of eddy currents in a uniaxially anisotropic plate. The model assumes that the plate is nonmagnetic and that the axis of uniaxial anisotropy is horizontal (i.e., lying in a plane parallel to the surface of the plate). The fields and currents induced by a general magnetic source are obtained by formulating the problem in terms of reduced electromagnetic potentials (Hertzian potentials) and making extensive use of integral transforms. Closed‐form expressions for the reduced potentials are given explicitly, enabling the induced fields to be calculated in all regions provided the free‐space source fields are known. The change in probe‐coil impedance &Dgr;Zdue to eddy‐current induction is considered in detail, and an explicit closed‐form expression for &Dgr;Zis derived for the general case. This general theory is illustrated by calculating &Dgr;Zfor a cylindrical air‐cored coil when (i) the coil axis is normal to the surface of the plate and (ii) the coil axis is tangential to the surface of the plate. The validity of these calculations was established by performing a series of measurements of &Dgr;Zusing an aluminum‐alloy sheet unidirectionally reinforced with boron fibers. The results of the theoretical calculations are in excellent agreement with experiment. The significance of the results for the nondestructive characterization of metal‐matrix composite materials is discussed.

ISSN:0021-8979    

DOI:10.1063/1.347171

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A photoresonant‐pumped x‐ray laser scheme using Be and Ne is considered. In this scheme the Beiv2p‐1stransition at 75.93 A˚ is used to pump the Nevii2s‐4plevel at 75.77 A˚. The wavelength mismatch can be decreased by either a bulk Doppler shift of the Be plasma produced by hydrodynamic expansion which requires a velocity of 6×107cm/s, or by opacity broadening of the Beivpump line, or by a combination of both. To investigate the viability of this particular scheme, preliminary studies were made of the Be plasma by focusing 14 to 24‐J, 3‐ns pulses of 1054‐nm laser light onto a planar Be target. Using a time‐of‐flight technique, it is found that the velocity needed to Doppler shift the Beivpump line into resonance with the Nevii2s‐4ptransition does not develop until at least 10 ns after the peak of the driving laser pulse. Spatially resolved time‐integrated spectral measurements indicate that by this time the Beivemissions have greatly decreased in intensity and this suggests that the needed bulk Doppler shift is difficult to achieve while still maintaining sufficient pump power. However, the observed opacity broadening of the Beivpump line (0.7 A˚ FWHM) is found to be sufficient to create significant spectral overlap between the nearly resonant lines to allow photopumping to occur. It is also observed that the temporal duration of the opacity‐broadened Beivemission is roughly 5 ns (FWHM), which is significantly longer than the 3‐ns driving laser pulse, and this fact can limit the efficiency of this particular x‐ray laser approach.

ISSN:0021-8979    

DOI:10.1063/1.346402

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A theoretical model of the formation and behavior of holographic gratings in photorefractive crystals, based on the assumption of two types of active centers being involved and simultaneous electron‐hole transport, is derived. A diffusion mechanism of recording is discussed. It is demonstrated that a photorefractive grating can change its phase by 180° during recording and erasure. At large angles between the recording beams, after a long recording or fixing the grating in darkness at room temperature, the grating decay is much slower than in the case when it is formed by diffusion and trapping of one type of carrier.

ISSN:0021-8979    

DOI:10.1063/1.346403

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Fringe‐locking techniques ar used for the recording of stable 90 ° phase‐shifted running holograms in photorefractive crystals. The use of this technique permits the characterization of a fast and a slow photoactive species in Bi12TiO20. We compare our results with those obtained from other methods and discuss the practical interest of this technique.

ISSN:0021-8979    

DOI:10.1063/1.346404

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Tungsten thin films onn‐InP layers have been investigated for potential use as a refractory ohmic contact for self‐aligned In‐based etched mesa buried heterostructure laser devices. The W films were rf sputter deposited onto InP substrates, S doped in the range of 1×1018–1×1019cm−3. The deposition parameters were optimized to produce films with the lowest possible induced stress, minimum argon content, and best morphology for as‐deposited wafers and after undergoing reactive‐ion etching and high‐temperature thermal cycles (700 °C), which are required for the self‐aligned technology. These parameters were obtained for films that were rf sputter deposited at a discharge power of 240 W and under argon pressure of about 10 mTorr. A thermal expansion coefficient of 5.84×10−6 C−1and a biaxial elastic modulus of 0.97×1012Pa were measured for the films. The electrical behavior of the W films sputtered onton‐InP was studied by means ofI‐Vand contact resistance measurements, which revealed a linear ohmic contact as‐deposited, while sputtered onton‐InP substrates, S doped to the level of 5×1018cm−3or higher. Rapid thermal processing at elevated temperatures improved the ohmic contact quality and decreased the specific contact resistance values to a minimum of 3.5×10−6&OHgr; cm2as a result of heating the W/InP (S doped 1×1019cm−3) at 600 °C.

ISSN:0021-8979    

DOI:10.1063/1.346405

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Rate equation analysis is presented to describe intracavity frequency conversions in laser systems consisting of two laser cavities combined with a nonlinear optical material. The optimum coupling conditions for sum or difference frequency generations and second harmonic generation are derived, and the existence of forbidden ranges in nonlinear coupling coefficients is discussed. For the practical application, effects due to beam walk‐off and acceptance angle are considered.

ISSN:0021-8979    

DOI:10.1063/1.346406

出版商:AIP    

年代:1990

数据来源: AIP