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The relative transition dipole moment function M(R) for the 4 3 R + ? a 3 R + electronic transition in the

We present experimentally derived potential curves and spin-orbit interaction functions for the strongly perturbed A {sup 1{Sigma}}{sub u}{sup +} and b {sup 3{Pi}}{sub u} states of the cesium dimer. The results are based on data from several sources. Laser-induced fluorescence Fourier transform spectroscopy (LIF FTS) was used some time ago in the Laboratoire Aime Cotton primarily to study the X {sup 1{Sigma}}{sub g}{sup +} state. More recent work at Tsinghua University provides information from moderate resolution spectroscopy on the lowest levels of the b {sup 3{Pi}}{sub 0u}{sup {+-}} state as well as additional high-resolution data. From Innsbruck University, we have precision data obtained with cold Cs{sub 2} molecules. Recent data from Temple University was obtained using the optical-optical double resonance polarization spectroscopy technique, and finally, a group at the University of Latvia has added additional LIF FTS data. In the Hamiltonian matrix, we have used analytic potentials (the expanded Morse oscillator form) with both finite-difference (FD) coupled-channel and discrete variable representation (DVR) calculations of the term values. Fitted diagonal and off-diagonal spin-orbit functions are obtained and compared with ab initio results from Temple and Moscow State universities.

We report high resolution measurements of 372 NaCs 5(3)Π(0)(v, J) ro-vibrational level energies in the range 0 ≤ v ≤ 22. The data have been used to construct NaCs 5(3)Π(0) potential energy curves using the Rydberg-Klein-Rees and inverted perturbation approximation methods. Bound-free 5(3)Π(0)(v, J) → 1(a)(3)Σ(+) emission has also been measured, and is used to determine the repulsive wall of the 1(a)(3)Σ(+) state and the 5(3)Π(0) → 1(a)(3)Σ(+) relative transition dipole moment function. Hyperfine structure in the 5(3)Π(0) state has not been observed in this experiment. This null result is explained using a simple vector coupling model.

Collisional satellite lines with |ΔJ| ≤ 58 have been identified in recent polarization spectroscopy V-type optical-optical double resonance (OODR) excitation spectra of the Rb(2) molecule [H. Salami et al., Phys. Rev. A 80, 022515 (2009)]. Observation of these satellite lines clearly requires a transfer of population from the rotational level directly excited by the pump laser to a neighboring level in a collision of the molecule with an atomic perturber. However to be observed in polarization spectroscopy, the collision must also partially preserve the angular momentum orientation, which is at least somewhat surprising given the extremely large values of ΔJ that were observed. In the present work, we used the two-step OODR fluorescence and polarization spectroscopy techniques to obtain quantitative information on the transfer of population and orientation in rotationally inelastic collisions of the NaK molecules prepared in the 2(A)(1)Σ(+)(v' = 16, J' = 30) rovibrational level with argon and potassium perturbers. A rate equation model was used to study the intensities of these satellite lines as a function of argon pressure and heat pipe oven temperature, in order to separate the collisional effects of argon and potassium atoms. Using a fit of this rate equation model to the data, we found that collisions of NaK molecules with potassium atoms are more likely to transfer population and destroy orientation than collisions with argon atoms. Collisions with argon atoms show a strong propensity for population transfer with ΔJ = even. Conversely, collisions with potassium atoms do not show this ΔJ = even propensity, but do show a propensity for ΔJ = positive compared to ΔJ = negative, for this particular initial state. The density matrix equations of motion have also been solved numerically in order to test the approximations used in the rate equation model and to calculate fluorescence and polarization spectroscopy line shapes. In addition, we have measured rate coefficients for broadening of NaK 3(1)Π ← 2(A)(1)Σ(+)spectral lines due to collisions with argon and potassium atoms. Additional broadening, due to velocity changes occurring in rotationally inelastic collisions, has also been observed.

Croissance de ZnSnP 2 sur differentes orientations de GaAspa epitaxie en phase liquide. Les meilleurs resultats sont obtenus sur les faces {100}. Determination des conditions de croissance permettant d'obtenir la phase chalcopyrite

A model is developed for the incorporation of donors and acceptors in epitaxial GaAs which indicates that the thin p‐type region often observed at the layer‐substrate interface in n−p+ structures is caused by the electric field associated with surface states and substrate doping. The model also predicts impurity gradients at the outer surface, about which little is known experimentally. Since results from the model are in agreement with many experimental observations, surface states and substrate doping are believed to be the major cause of impurity gradients in epitaxial GaAs.

Column‐IV (Si, Ge, and Sn) and column‐VI (S, Se, and Te) impurities are used to dope high‐purity layers of vapor epitaxial GaAs. Resistivity and Hall data on a large number of samples show that the common donors in GaAs (assumed to be column‐IV impurities on gallium sites and column‐VI impurities on arsenic sites) are compensated by acceptor centers which are donor impurity‐vacancy complexes. These acceptor complexes are tentatively identified as column‐IV impurities on gallium sites associated with single gallium vacancies and column‐VI impurities on arsenic sites associated with single arsenic vacancies.

The exciton energy spectrum in GaAs has been studied by photoluminescence and reflection. The photoluminescence was excited using a krypton laser (6471 \AA{}). We observed for the first time the spectra for the excited states of the free exciton in GaAs and also the spectra for the ground states in zero field and in the field range from 12 to 40 kG. The value for the exciton binding energy was determined to be (4.20 \ifmmode\pm\else\textpm\fi{} 0.3) \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}3}$ eV from which the band-gap energy of 1.5195 \ifmmode\pm\else\textpm\fi{} 0.0005 eV has been deduced. The values for the Zeeman splitting factors for electron ($g$ factor) and hole ($\ensuremath{\kappa}$ parameter) were deduced from these measurements to be ${g}_{c}=\ensuremath{-}0.50\ifmmode\pm\else\textpm\fi{}0.05$ and $\ensuremath{\kappa}=1.0\ifmmode\pm\else\textpm\fi{}0.2$, respectively. A phenomenological description for the free-exciton energy spectrum in the intermediate-field regime is used to explain the experimental measurements.

The magnetic‐field dependence of the Hall factor is investigated theoretically and experimentally. The theory includes arbitrary band structure, carrier degeneracy, and wave functions assuming isotropic media and carriers behaving as spinless Fermions without energy‐level quantization. Comparisons between theory and experiments on high‐purity GaAs from the low magnetic‐field limit to the classical high magnetic‐field limit agree to within 0.7 percent.

We have developed a model of Cr in GaAs which is consistent with a large body of experimental data. It relies or recent spectroscopic models and on our interpretation of redistribution and electrical data, all of which indicate the existence of Cr complexes. The existence of rapidly diffusing interstitial Cr donors is assumed and justified. The model offers a unified picture of the effects of implantation on the Cr profile. It contains mechanisms for compensation and redistribution, which offer an explanation of the semi-insulating properties of Cr doped GaAs and of the two apparently incompatible classes of diffusion and anneal data. The redistribution depends on how the Cr was incorporated and on the vacancy concentration profiles. A study of representatives of the two classes of redistribution data allows us to estimate a lower limit of interstitial Cr diffusion constant and of the vacancy diffusion lengths in GaAs.

Using back reflection Laue measurements we have examined the substrate orientation dependence of antiphase domain boundaries for ZnSnP2 (c= 2a) grown on GaAs by liquid phase epitaxy. These results together with those of other workers indicate that {211} substrates are best for the growth of chalcopyrite layers withc= 2a, while {100} substrates are best for those chalcopyrites withc

C-V analysis of n-type InP using metal-semiconductor Schottky contacts is inadequate for determining free carrier concentration vs. depth profiles due to low barrier heights, uncontrolled oxide formation, and metal semiconductor chemical reactions. Concentration vs. depth profiles can be obtained over a wide range of carrier concentrations to virtually unlimited depth using electrochemical C-V (ECV) analysis. However, the 0.5M HCl in aqueous solution reported in the literature is not ideal for the anodic dissolution of InP. This work reports an improved anodic etchant for ECV profiling of n-type InP and the design of a constant current etch, difference method ECV profiler utilizing a new sample mounting technique.

The chalcopyrite alloy ZnxCd1−xSnP2 is a potentially use-ful electronic material. In addition to having effective masses lower than and energy gaps similar to its III-V compound analogs, this alloy can also be lattice matched to InP. We have used an open-tube, sliding-boat, liquid-phase system to grow ZnxCd1−xSnP2 epitaxially on InP sub-strates. Unintentionally-doped layers have electron con-centrations as high as 3 × 1019cm−3 with mobility values of about 2,000 cm2/V-sec. These mobility values are sub-stantially larger than have been obtained in the equivalent III-V materials at similar concentrations.

The distribution of impurities incorporated in epitaxial layers during their growth is determined by diffusion due to concentration gradients and by drift in the built-in electric field. This problem has been previously treated in the approximation that the impurities reach their equilibrium distribution during growth. We have extended this calculation to treat impurity drift and diffusion under non-equilibrium conditions, a situation much more characteristic of most realistic growth condi-tions. In the new calculation, the solution of the Shockley-Poisson problem is exact and the boundary con-dition at the growth interface is an approximation based on the electrostatics of surface states. The new calcu-lation also permits consideration of outdiffusion from the substrate, a phenomenon of technological significance. It is also capable of modeling variations of source im-purity concentration and growth rate during epitaxial growth. Calculations modeling n-type GaAs epitaxy of practical interest are presented.

In this paper we present a simple model for an inhomogeneous semiconductor which leads to an anomalously high apparent mobility. The model consists of a cylindrically symmetric van der Pauw measurement with a conducting inhomogeneity. This model is analyzed quantitatively and verified experimentally for several measurement configurations. The results cast doubt on the use of a high mobility as an indication of the quality of a semiconductor unless the homogeneity is unambiguously determined or the magnetic field dependence of the Hall constant is carefully examined.

The combination of polar optical phonon, piezoelectric acoustic photon, deformation potential acoustic phonon, ionized impurity, and neutral impurity scattering in the relaxation time approximation is shown to give results which are in good agreement with the temperature and concentration dependence of the electron mobility in high‐purity GaAs. For polar optical phonon scattering a relaxation time is defined at each temperature from Ehrenreich's variational calculation. Since most of the parameters are well known, the only adjustable parameter in the calculation is the conduction band deformation potential with the best agreement with experiment given by | E1 | = 7.0 eV. Using this value a 77°K lattice scattering limited mobility of 240 000 cm2/V sec is obtained.

The preparation of single‐crystal GaAsP by halide vapor transport is described. That dislocation free GaAsP can be achieved was verified experimentally for whiskers grown by the vapor‐liquid‐solid method. In the growth of monocrystalline ingots for device purposes, growth mechanics and the resulting crystal habit are strongly influenced by degenerate Zn, Te, and Se doping. Since n‐type crystals require higher supersaturations, single‐crystal growth is easier to obtain with Zn doping.The as‐grown dislocation structure of ingots with low‐index natural facets is examined by decoration and etching. Typical densities are 5×103 to 106/cm2. From their simple crystallographic orientations different dislocations are identified. 〈211〉, {111} and 〈100〉, {110} edge dislocations are observed in {110} polygonization walls. Values of mobility and carrier density are evaluated from a device point of view. Laser diodes with threshold currents as low as 3000 A/cm2 at 33.3% GaP have been obtained from this material.

Zero‐bias Schottky barrier capacitance measurements indicate the presence of heavily‐doped surface impurity gradients in n‐type epitaxial layers of GaAs grown on n+ substrates. These impurity gradients are produced during epitaxial growth by the electric field due to 5×1011 cm−2 surface states in GaAs in 1000 K. For n‐type layers grown on Cr‐doped substrates, high‐resistance regions are observed at the surface. These regions are probably caused by the buildup of positively charged chromium atoms in the electric field at the surface. The redistribution of chromium atoms in ion‐implanted samples during annealing can also be explained by electric fields due to surface states and the implanted‐ion profiles.

Below band‐gap photovoltaic response with a half‐power point at 1.31 eV is observed in p‐type In1−xGaxP on n‐type GaAs heterojunctions with {111} interfaces. This response is apparently due to photon‐assisted tunneling of carriers across the interfacial energy gap, which is smaller than the energy gaps of the constituent materials. The same mechanism can be employed in other heterojunctions with appropriate energy‐band lineups to obtain longer wavelength infrared response.

Integrated structures consisting of a double‐heterostructure GaAs‐AlGaAs etched‐mesa Fabry‐Perot laser coupled to a high‐purity GaAs waveguide have been fabricated and tested. Room‐temperature threshold current densities as low as 7.5 kA/cm2 for 1‐μm‐thick active layers were measured.

Photothermal ionization measurements on Si‐doped GaAs grown by molecular beam epitaxy (MBE) have indicated that the previous identification of the Si donor peak was incorrect. Data leading to the new identification are presented and the results leading to the earlier identification are re‐examined. Implications of the new identification for the importance of Si as a residual donor in epitaxial GaAs grown by various techniques are discussed.

GaAs electroabsorption avalanche photodiodes in n‐n+ GaAs waveguides have been used to detect the 1.06‐μm radiation from a Nd : YAG laser with a responsivity of 125 A/W and an internal quantum efficiency of 23%. The response at this wavelength is due to a combination of band‐to‐band and defect‐to‐band electroabsorption.

We have measured the lasing energy of optically pumped high‐purity GaAs from 2 to 300 K. Low‐temperature results show strong many‐body effects in the band‐to‐band lasing below the single‐particle band‐gap energy, and the high‐temperature data indicate that the lasing energy approaches the band gap measured by photoconductivity.

A high‐purity GaAs sample with a measured room‐temperature mobility of 15 200 cm2/V sec is examined in detail. Resistivity and Hall measurements are in reasonable agreement with a previously developed model which shows that conducting inhomogeneities can result in anomalously high measured mobilities. A sizeable number of precipitates (probably gallium) are observed in the sample.

Uniform avalanche Schottky barrier photodiodes have been fabricated by plating a thin layer of platinum on GaAs and forming a guard ring by proton radiation. Operating at a gain of 100 these photodiodes exhibit gain‐bandwidth products greater than 50 GHz and enhanced signal to noise ratio in excess of 30 dB. The observed variation on the spectral response with bias can be accounted for by a change in the absorption of the Schottky barrier diode.

Although a number of mechanisms have been proposed to explain the existence of impurity gradients in epitaxial GaAs, the impurity gradient model presented in this report shows that such effects are inherent to the growth process. That is, when the carrier concentrations in the substrate, growing layer, and at the growth surface are different at the growth temperature, non-uniform time-dependent electric fields are obtained in the layer. These fields can enhance or retard the motion of ionized impurities and defects during growth producing impurity gradients at the outer surface and different conductivity regions at the epitaxy-substrate interface. High temperature resistivity and Hall coefficient measurements were made on epitaxial layers and substrates and analyzed using a self-consistent four-band model to obtain quantitative results for the impurity gradient model for growth on heavily-doped n-type substrates predicts that thin (0.05 micrometers or larger) p-type regions at the epitaxy-substrate interface will be produced under conditions commonly encountered in the epitaxial growth of GaAs.

The purpose of this study was to create a reliable, valid instrument to identify the major stressors experienced by new transplant recipients and to establish baseline data. Sixty transplant recipients (85% of sample) responded to a mailed questionnaire. From a list of 44 possible stressors the subjects self-reported the possibility of rejection as the major stressor. Recommendations include using the instrument (KTRSS) in clinical practice to plan individualized care based on an assessment of the client's perception of stressors following transplantation and educating clients about the stressors common to the transplant recipient.