摘要:

Surface morphology, electron mobility, and photoluminescence (PL) spectrum have been investigated for the epitaxial layers of GaAs on (0001) sapphire grown at several temperatures. The optimum growth temperature range is determined to be around 690 °C. The mobility and the PL intensity efficiency are improved by increasing the layer thickness, due to the decrease of defect density. The structure related to the defects is located at a wavelength of 1.04 &mgr;m in the PL spectra. We fabricate the first field‐effect transistor on GaAs on sapphire, and it has a transconductance of 20 mS/mm for a gate length of 2.5 &mgr;m.

ISSN:0021-8979    

DOI:10.1063/1.337680

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

We have examined the possibility of using a realistic laser system to produce uniform illumination of a direct drive laser‐fusion pellet. This laser system consists of a short wavelength laser (KrF, &lgr;=0.25 &mgr;m) with the induced‐spatial‐incoherence method. A numerical analysis describes the laser beams propagating through the pellet plasma, energy deposition by inverse bremmstrahlung absorption, and energy conversion to ablation drive pressure. The results indicate that highly uniform (&Dgr;P/⟨P⟩<2%) distributions can be produced while a large fraction of the laser beam energy (>75%) is simultaneously absorbed. The spatial structure of the distribution is also analyzed and found to contain primarily low spatial frequencies with maximum magnitudes less than 0.5%. Misalignment of the laser beams increases the overall nonuniformity by about 1.5% for every 1% increase in the relative misaiming error (measured as a percentage of the pellet radius). A maximum misalignment error on the order of a few microradians in the final optics is suggested by this analysis.

ISSN:0021-8979    

DOI:10.1063/1.337631

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The Monte Carlo computer programtrimis used to calculate the projected range, the standard deviation, the skewness, and the kurtosis of implanted boron ion distributions in silicon, silicon dioxide, molybdenum disilicide, tantalum disilicide, titanium disilicide, and tungsten disilicide. The boron implantation energy ranges from 10 to 500 keV.

ISSN:0021-8979    

DOI:10.1063/1.337677

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The production of negative hydrogen ions sputtered from a low work function converter surface has been investigated. Hydrogen and cesium admitted into the vacuum chamber are chemisorbed on a polycrystalline molybdenum target. H−, Mo−, ande−are sputtered from this cathode by Cs+ions in the energy range 150–1000 eV. Angular and parallel energy distributions of H−, Mo−, ande−are measured as a function of hydrogen gas pressure, cesium coverage, and incident ion energy. For optimum coverage, the H−ion temperature varies from 0.65% and 0.35% of the incident Cs+bombarding energy for Cs+ion energies of 250 and 1000 eV, respectively. The secondary electrons have a temperature of 0.04% of the bombarding energy almost independent of Cs+energy. The spreads increase with decreasing target coverage and are independent of surface roughness. The optimum H−, Mo−, ande−yields are also measured as a function of hydrogen pressure and incident Cs+bombarding energy. The optimum H−ion yield is 0.41 at a Cs+ion energy of 750 eV. By extrapolating the H−ion yield at low Cs+bombarding energy, a Cs+ion threshold energy of 120 eV may be estimated. This indicates a binding energy of hydrogen smaller than 3.6 eV.

ISSN:0021-8979    

DOI:10.1063/1.337800

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

An improved pulsed Townsend technique for the measurement of electron transport parameters in gases is described. The accuracy and sensitivity of the technique have been investigated by performing, respectively, electron attachment coefficient measurements in pure O2over a wide range ofE/Nat selected O2pressures and by determining the electron attachment and ionization coefficients and electron drift velocity in CH4over a wideE/Nrange. Good agreement has been obtained between the present and the previously published electron attachment coefficients in O2and for the drift velocity measurements in CH4. The data on the electron attachment coefficient in CH4(measured for the first time) showed that with the present improved pulsed Townsend method, electron attachment coefficients up to 10 times smaller than the ionization coefficients at a givenE/Nvalue can be accurately measured. Our measurements of the electron attachment and ionization coefficients in CH4are in good agreement with a Boltzmann equation analysis of the electron gain and loss processes in CH4using published electron scattering cross sections for this molecule.

ISSN:0021-8979    

DOI:10.1063/1.337690

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Clusters ofmolecularhydrogen have been detected at a concentration of 930 ppm H2in electroless Cu deposits using a new, nondestructive, calorimetric technique. The H2is located in microvoids at a pressure of 700 atm at room temperature. The observation of H2supports previous suggestions that it is responsible for the embrittlement of electroless Cu. Gentle annealing at 150 °C restores the ductility and also removes the H2.

ISSN:0021-8979    

DOI:10.1063/1.337656

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Four gain models are developed for use in analyzing source‐flow chemical laser resonators. The first is a rotational nonequilibrium (RNE) model which traces the evolution of each vibrational‐rotational state of the lasing molecule. The second is a less detailed model based on the assumption that each vibrational level is in rotational equilibrium (RE). In the third model, in addition to the rotational equilibrium assumption, the gain is assumed to be the same for all the vibrational transitions. The equations then become identical in form to those describing single‐line (SL) lasing from a two‐level system. The RE and RNE models solve the chemical kinetics equations for the gain self‐consistently with the gasdynamic equations describing the flow field. In the SL model coupling between the gasdynamics and the laser kinetics is eliminated by using the gasdynamics from a simple Fabry–Perot calculation at a representative value of the threshold gain to provide the flow field conditions for the resonator calculation. A fourth gain model investigates the effect of using the gasdynamic calculation from the simpler SL model in a rotational nonequilibrium kinetics model. The objectives of the study are to determine how well the more computationally efficient RE and SL models can reproduce the predictions of the RNE model, and to determine the error introduced by decoupling the solutions to the gasdynamic and laser kinetic equations. The impact of rotational nonequilibrium phenomena on lasing performance is also assessed. Comparisons for the specific case of a HF laser indicate that both the RE and SL models predict output powers and peak‐power mode widths which are in good agreement with those predicted by the RNE model over a wide range of values for the resonator gain. Furthermore, the RE model well approximates the power distribution among the vibrational levels, although only the RNE model is capable of providing detailed spectral information. We also find that decoupling the gasdynamic and kinetic equations does not significantly impact the accuracy of the resonator calculation. The utility of the more computationally efficient models in the design of source‐flow chemical laser resonators is discussed.

ISSN:0021-8979    

DOI:10.1063/1.337664

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The governing equations for the transitional fluid motion and pit contour induced by the laser marking and the thermocapillary are derived. The rate of thickness change is controlled by two factors: the surface tension force and the gravitation force; the former is much more important than the latter. The temperature rise in a thin optical layer is calculated based on the Poynting vector theorem. Calculated results indicate that the temperature profile follows a Gaussian distribution, and is in agreement with previous reports. Mathematical modeling shows that the rate of pit formation is strongly related to the surface tension, melt viscosity, layer thickness, and optical properties of the recording layer. The effects of the marking conditions, substrates, and convectional heat transfer on pit contour are also determined. In addition, the limitations of this model are discussed in detail.

ISSN:0021-8979    

DOI:10.1063/1.337627

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Available optical output powers from the Ga1−xAlxAs lasers are limited by the catastrophic optical damage or output power saturation due to local heating on the facet. Especially, the saturation of current‐optical output power characteristically occurs during the operations at relatively low output power. This report describes the degradation process in an active region for lasers with the striped window as an electrode with respect to current‐optical output power characteristics, electroluminescence image observation, and measurement of temperature rise at the facet and the cavity inside using laser Raman spectroscopy. The nonluminescing dark region observed in rapidly degraded lasers develops from the facet to the cavity inside. The dark region is so nonradiative that electron‐hole recombination in that region produces heat rather than light. The measured local temperature on the facet drastically rises and the area influenced by local heating extends into the cavity inside. Although the threshold current increases by only 16%, the optical output power is saturated and finally the initial optical output power (20 mW/facet) is hardly maintained. It is found that the change in current‐output power characteristics almost corresponds to the calculated results which incorporated temperture dependence of local absorption loss in the dark region.

ISSN:0021-8979    

DOI:10.1063/1.337628

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The lateral coherence of broad‐area lasers fabricated from a GaAs/GaAlAs graded index waveguide separate confinement and single quantum well heterostructure grown by molecular‐beam epitaxy was investigated. These lasers exhibit a high degree of coherence along the junction plane, thus producing a stable and very narrow far field intensity distribution.

ISSN:0021-8979    

DOI:10.1063/1.337629

出版商:AIP    

年代:1986

数据来源: AIP