摘要:

This paper presents a review devoted to the problem of how optical and structural properties of quantum‐well heterostructures (QWH) can be correlated in detail, and how these properties may be connected with the parameters of the epitaxial growth process. It demonstrates how luminescence techniques, mainly photoluminescence (PL) and cathodoluminescence imaging (CLI), may be used for evaluation of the structural disorder on the atomic scale, which occurs at the growth surfaces creating the interfaces of the QWH. The physics of the excitonic luminescence in QWH (theory and experiment) is presented in detail in the first part of the review. This is followed by a comprehensive discussion of experimental aspects (hardware and software) of the luminescence techniques, as applied for studying QWH grown by molecular‐beam epitaxy (MBE) and metalorganic vapor phase epitaxy (MOVPE). The specific features of both the epitaxial growth techniques, when used for growing QWH are presented in the next part of this review. Finally, the possibilities of application of PL and CLI to studies on growth of QWH by MBE and MOVPE are demonstrated on a couple of selected examples. The review concludes with a short discussion on possible interpretation mistakes which may occur when one applies the CLI to studies of interfaces in QWH without taking into account the basic parameters of the excitonic luminescence lines creating the CL images of the relevant interfaces.

ISSN:0021-8979    

DOI:10.1063/1.349613

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Elastic differential and total cross sections for positrons, from 5 eV to 10 keV, and for electrons, from 50 eV to 10 keV, scattered by bound gallium and arsenic atoms have been calculated using the method of partial waves. The optical potential consists of a static potential, a Buckingham‐type polarization potential, and the Mittleman–Watson exchange potential (for electrons). Low‐order partial wave phase shifts are computed by numerical integration of the radial part of the Schro¨dinger equation. For higher orders, a closed analytic expression is obtained in the first Born approximation for the phase shifts. The calculated total cross sections are parametrized in terms of the screened Rutherford cross section to be used in Monte Carlo transport codes.

ISSN:0021-8979    

DOI:10.1063/1.350362

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The deposition of low‐energy carbon atoms onto a low‐temperature diamond (111) surface is studied by molecular‐dynamics computer simulations. A Stillinger–Weber potential [F. H. Stillinger and T. A. Weber, Phys. Rev. B31, 5262 (1985)], with a reparametrization derived from quantum‐mechanical energy calculations for small tetrahedral carbon clusters, is used to model the interatomic interactions. The penetration of 1–100‐eV neutral carbon atoms into the diamond (111) surface at 100 K and the resultant surface atom rearrangements and induced film stress are studied. For intermediate energies (20–60 eV) the incident atom penetrates beneath the exposed (111) surface and significantly increases the lateral compressive stress in the diamond film. The emerging picture is that diamond films grow from below the exposed surface in a region of locally high stress and tetrahedral coordination.

ISSN:0021-8979    

DOI:10.1063/1.349653

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We have theoretically investigated the output performance of a pulsed discharge initiated H2/F2chain first vibrational overtone HF chemical laser. The model used included rotational relaxation processes and simulated simultaneously both fundamental and overtone oscillations since the undesirable fundamental lasing cannot completely be suppressed during the experimental overtone oscillation. In the H2/F2chain reaction system, which can produce the highly vibrationally excited HF(v) molecules up to vibrational levelv=6, higher overtone output energy can be expected due to the increased vibrational overtonePbranches, the increased transition probability of the first overtone transitions at the higher vibrational levels, and to the relative longer gain duration of a few tens microseconds. The overtone output energy of 2.73 J/lis obtainable from the laser gas mixture of F2/H2/He=10/4/786 (Torr). Adding He diluent gas can effectively suppress the undesirable fundamental lasing by pressure broadening; the overtone output energy is much less sensitive to this effect. The overtone output energy is found to be dependent on the residual reflectivity of the resonator mirrors over the fundamental lasing band.

ISSN:0021-8979    

DOI:10.1063/1.349654

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The degradation during cw operation or under electron beam bombardment of the graded index separate‐confining heterostructure laser devices grown on Si and on GaAs substrates was investigated. The induced current and the cathodoluminescence modes of a scanning electron microscope were used to observe the cleaved face of these devices as a function of the stage of degradation. Our findings strongly suggest that the degradation starts owing to a mechanism of donor annihilation and complex formation within the space‐charge region of the device. Two different methods allowing the evaluation of the donor concentration within the depletion zone were developed. One method is based on the measurement of the direct bias necessary to recover the initial microscopic characteristics of a damaged device. The other one relies on a numerical calculation of the partition of nonequilibrium carriers which takes into account the detailed structure of the device. This calculation is based on a three‐dimensional analytical function describing the energy losses of the primary electrons.

ISSN:0021-8979    

DOI:10.1063/1.349655

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The photorefractive (PR) degenerate four‐wave mixing (DFWM) of polarized electromagnetic waves in cubic isotropic crystals is considered. Effects of cross‐polarization coupling have been investigated in the case of DFWM in absorbing, semi‐insulating compound semiconductor PR crystals in reflection geometry. Considering the pump beam depletion, nonlinear coupled wave equations are obtained and have been solved numerically by a shooting method. Numerical results obtained from computer calculations are presented in graphical form. It is observed that the intensity of a particular polarization component can be appreciably increased by a proper choice of input beam polarization angle, crystal orientation, and crystal thickness.

ISSN:0021-8979    

DOI:10.1063/1.349656

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Photoluminescence characteristics of uniformly silicon‐ and beryllium‐doped pseudomorphic InGaAs‐GaAs‐AlGaAs single‐ and multiple‐quantum‐well heterostructures grown by molecular‐beam epitaxy are studied. Red shifts in the photoluminescence peaks are obtained from uniformly silicon‐doped single‐quantum‐well samples with respect to undoped samples. Uniformly beryllium‐doped InGaAs‐GaAs multiple quantum wells totally intermix during materials growth. Also, the effect on laser performance (laser thresholds and emission spectra) by silicon doping is demonstrated with an InGaAs‐GaAs‐AlGaAs strained‐layer laser (grown by molecular‐beam epitaxy) with a heavily silicon‐doped quantum well. The low laser threshold, kink in light versus current, shift in emission wavelength, and two emission peaks are observed, and these characteristics are believed to be due to heavy silicon doping.

ISSN:0021-8979    

DOI:10.1063/1.349657

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

A new method of fabricating fiber optic surface polariton polarizers is described which produces devices with well‐defined lengths and fiber core to flat spacings. The results of experiments investigating the length dependence of the extinction ratio are interpreted through the use of a new theoretical analysis. Successful investigations of the dependence of the extinction ratio on the fiber core to flat spacing should be possible with further fabrication modifications.  

ISSN:0021-8979    

DOI:10.1063/1.349658

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The mirage effect within a transparent solid substrate was used for monitoring optical absorption of a thin film. Refractive index gradients, which accompany thermal gradients below the film‐coated surface, cause a probe laser beam to be deflected. The spectrum of copper, deposited onto a piece of clear acrylic, was recorded by this method of photothermal deflection. The influence of thermally induced mechanical stresses can alter the effective value of the thermo‐optic coefficient of the solid,dn/dT.

ISSN:0021-8979    

DOI:10.1063/1.349659

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Quantitative measurements of ablated material from the surface of polyethyleneterephthalate (PET) by 248‐nm excimer laser fluences up to 10 J/cm2are performed by HeNe laser‐beam deflection in vacuum and by photoacoustic depth profiling in air. HeNe laser‐beam deflection measures the density of gas phase material present in the ablation plume. Photoacoustic depth profiling is a nonintrusive diagnostic that directly measures the etch depths from laser ablation. A hydrodynamic model consisting of a centered rarefaction wave that reflects off the PET surface is shown to describe the laser deflection signals. From these measurements an estimate of the initial temperature of the ablated species is found.

ISSN:0021-8979    

DOI:10.1063/1.349660

出版商:AIP    

年代:1991

数据来源: AIP