摘要:

Buried ridge structure GaInAsP/InP lasers with stripes parallel to ⟨011⟩ and ⟨01¯1⟩ directions (designated type A and B, respectively) were fabricated by MOVPE regrowth. Type A lasers exhibit considerably lower threshold current, higher maximum output power, and higher yield than type‐B devices. Secondary ion mass spectroscopy depth profiles taken with high spatial resolution using the checkerboard matrix gate technique reveal elemental distributions as expected for type‐A lasers, but the following unexpected results were observed for type B structures: A considerable amount of phosphorus is found in the GaInAs above the laser stripes, which is correlated with a reduced gallium concentration and a higher proportion of indium. Zinc, diffused into the GaInAs to make ohmic contacts, has a reduced concentration above the laser stripes, but occasionally exhibits exceptionally high concentrations with strong localization. The sputter rate in a region extending up to 15 &mgr;m on both sides of the laser stripe is significantly enhanced after zinc diffusion into the top GaInAs layer of type B structures. The observed anomalies are attributed to reduced crystalline perfection of the InP regrown above ⟨01¯1⟩ oriented laser stripes. The lower crystallinity favors efficient phosphorus outdiffusion from the InP during growth of the GaInAs and it also enhances zinc diffusion. The experiments emphasize the need to optimize the growth parameters for MOVPE regrowth above ⟨011⟩ and ⟨01¯1⟩ oriented structures separately.

ISSN:0021-8979    

DOI:10.1063/1.346487

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Seven fibers of different cross‐sectional shape are studied interferometrically using multiple‐beam Fizeau fringes. These fibers are of circular, rectangular, triangular, trilobal, elliptical, kidney, and dog‐bone cross‐sectional shapes. The areas enclosed under the interference fringe shift is considered to represent the optical path difference integrated across the fiber. This principal is applied to nylon 6 fibers of trilobal cross‐sectional shape. The described method is suitable for the measurement of refractive indices of any fiber with regular or irregular transverse sections. Microinterferograms are given for illustration.

ISSN:0021-8979    

DOI:10.1063/1.346488

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A theoretical investigation of the effect of induction frequency shows that deviations from local thermodynamic equilibrium (LTE) are strongly related to this parameter. Computations are carried out for an argon plasma at atmospheric pressure over the frequency range 3–40 MHz. Higher frequencies result in lower‐temperature levels in the torch, and also the difference between the electron and the atom/ion temperatures is increased. This is in agreement with the observations of other investigators. The results of the proposed model also show good agreement with the measured temperature profiles. Similar calculations, which are based on the LTE assumption, are reported and compared with the present non‐LTE model.

ISSN:0021-8979    

DOI:10.1063/1.346489

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A technique for sampling negative ions in hollow‐cathode and hollow‐anode discharges of strongly electronegative gases is presented. The negative ions were mass analyzed to be Cl−, Cl−2, and Cl−3for the discharge of Cl2/N2mixture and Cl−for HCl/N2. The dependence of negative ion intensity on gas pressure and discharge voltage was investigated. Photodetachment of negative ions was used to induce photoelectron transient signals that probe ion concentrations. The transient signal indicates that negative ions originate in discharge, but not in the mass‐analyzer region. Time dependence of the negative ion signal induced by laser irradiation was measured by a quadrupole mass analyzer and used to study the kinetics of charged particles responsible for the transport of laser‐induced perturbation. The observed negative ion transient signal is a useful means for studying negative ion kinetics in plasma.

ISSN:0021-8979    

DOI:10.1063/1.346490

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The radio‐frequency glow discharges of several kinds of gases were examined to measure the ion sheath thickness at the cathode electrode. At intermediate gas pressures around 0.05– 0.5 Torr, the sheath thicknessddepends on the pressurePin the expressionP1/2d=K0for almost all of the discharges examined. It was also pointed out that the constantK0value decreased linearly against a mass of the predominant ion in the plasma. The discrepancy between the sheath thickness measured in this work and by theoretical solution was discussed for the argon discharge.

ISSN:0021-8979    

DOI:10.1063/1.346491

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A low‐pressure mercury‐argon discharge is probed with a new technique of laser spectroscopy to determine the influence of the Hg(63P2) population on discharge emission. The discharge is excited with inductively coupled rf power. Variations in the intensity of emission lines in the discharge were examined as &lgr;=546.1 nm light from a cw laser excited the Hg 63P2‐to‐73S1transition. The spectrum of the discharge viewed in the region of laser irradiation showed increased emission in &lgr;=546.1, 435.8, 404.7, 253.7, and 194.2 nm lines. Other lines in Hgiexhibited a decrease in emission. When the discharge was viewed outside the region of laser irradiation, all lines exhibited an increased emission. Based on these results we conclude that the dominant mechanism for the excitation of higher lying levels of mercury is the two‐step electron impact excitation via the3P2level. The depopulation of the metastable level is also responsible for the observed increase in the electron temperature when the laser irradiates the discharge. We also conclude that the3P2metastable level of mercury does not play a significant role in the excitation of the2P1/2level of mercury ion.

ISSN:0021-8979    

DOI:10.1063/1.346492

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The radio‐frequency excited helium discharge is modeled as an equivalent circuit in order to account for the electrode‐sheath coupling, which includes an electrode and a sheath capacitance. The results obtained from the solution for the sheath thickness and reactance are used in conjunction with the known uniform plasma column characteristics to obtain the required voltage needed to sustain the current flow through the discharge. The calculations give that the value of the electron density at the sheath edgensvaries between 12%–16% of the centerline electron densityne0, whereas the root mean square of the sheath thicknesssˆ assumes values between 6% and 11% of the pipe radiusa. Both curves are increasing with increasing current flow through the discharge. The order of magnitude of the electrical conductivity achieved by the 11‐MHz radio frequency for the pressure range of 405.33–506.67 Torr, temperature range of 483–510 K, velocity range of 449–485 m/s, in a pipe of radius 0.011 m, is varying from 0.01 to 0.07 mho/m, which is comparable to the lower limits of the ionization achieved under thermal equilibrium for a gas seeded with a few percent of a low ionization potential substance. The comparison of the theoretical estimates for the applied voltage‐current curve with the experimental measurements show general agreement and are within±10%, and support the theory that the major loss of the applied voltage occurs in the electrode‐sheath region, especially at the higher values of the current flow through the discharge.

ISSN:0021-8979    

DOI:10.1063/1.346466

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

This study carries out numerical calculations using the ‘‘theory for rf ionization of noble gases with turbulent flow based on a two‐electron group model,’’ which was developed in order to investigate the problem of ionizing a high speed neutral gas by the application of an external rf electric field. The plasma model is described by the electron energy and the particle balance equations and accounts for the high‐speed neutral gas flow through the turbulent diffusion coefficient and the convection loss term. The calculated results based on the two‐electron group model demonstrate that theI‐Vcurves are affected by the magnitude of the turbulent diffusion coefficient, the high‐speed flow affects the discharge parameters through the turbulent diffusion coefficient and through the convection loss term, and as the electron density is increased the electron‐electron interactions became more intense and the distribution function approaches a Maxwellian at a single electron temperature. The numerical evaluation of the energy exchange terms between the two groups of electrons show that the bulk electrons attain their temperature primarily by the balance between the energy gain due to the electric field and the energy loss due to the elastic collisions with the neutrals and ions, and the tail electrons gain energy primarily by the electron‐electron collisions and by the bulk to tail conversion due to the applied electric field, and loose energy primarily by the excitation from the ground level and by the tail to bulk electron conversion due to elastic collisions. The results of calculations for two particular cases indicate that for pressure in the range of 400–510 Torr, temperature in the range 480–511 K, velocity in the range 449–485 m/s, ionizer tube diameter of 0.022 m, one can attain electron densities in the range 1017–1018m−3with the application of moderate rf electric fields in the range of 200–400 V/cm.

ISSN:0021-8979    

DOI:10.1063/1.346467

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Spatially resolved arc temperatures and sodium density measurements are presented for two high‐pressure sodium arcs. Absolute intensities of the optically thick 818/819‐nm lines were used to determine the arc temperature while the radial profile of the optically thin 514‐nm line was Abel inverted to determine the Na atomic density. Agreement with an independent measurement of the Na density obtained by controlling pressure of sodium in the lamp with a tin bath consistently required a value for the Na 514‐nm transition probability 2–3 times smaller than the literature value (A=0.011×108s−1) of Wiese, Smith, and Miles [AtomicTransitionProbabilities, NSRDS‐NBS 4 (NBS, Washington, DC, 1971), Vol. II], obtained from quantum mechanical calculations. The results of three separate experiments indicate that the value should be modified toA=0.0040×108s−1with a standard deviation of ±21%. A more detailed error analysis including systematic error would indicate an accuracy to within ±33%.

ISSN:0021-8979    

DOI:10.1063/1.346468

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Sequential sputter deposition of amorphous 4‐nm‐thick Ta and 7‐nm‐thick Si layers leads to the formation of a periodic multilayer that can be regarded as a synthetic one‐dimensional crystal. A simple kinematical diffraction model is presented to discuss x‐ray diffraction patterns obtained from the multilayer structure during annealing. Post‐deposition annealing up to temperatures above 530 °C, where the lattice structure disappears, leads to Si diffusion into the Ta layers forming a nonstoichiometric Ta‐Si phase. The high diffusion rate of Si in Ta leads to a homogeneous distribution of Si in the Ta (silicide) regimes. As shown by cross‐sectional transmission electron microscopy, the interfaces remain sharp during the interdiffusion process. This makes the observation of low‐angle Bragg reflections up to the 12th order possible. The local atomic structure around the Ta atoms was analyzed by measuring the extended x‐ray‐absorption fine structure above the TaLIIIedge at different probing depth conditions. During annealing the local Ta environment was found to be TaSi2like, even if only a small portion of the Si has diffused into the Ta layers, and the silicide formation is far from stoichiometry. The formation of a Ta suboxide was detected in the surface region of the top Ta layer.

ISSN:0021-8979    

DOI:10.1063/1.346469

出版商:AIP    

年代:1990

数据来源: AIP