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Indium-based micro-bump arrays, among other things, are used for the bonding of infrared photodetectors and focal plane arrays. In this paper, several aspects of the fabrication technology of micrometer-sized indium bumps with a smooth surface morphology were investigated. The thermal evaporation of indium has been optimized to achieve ~8 μm-thick layers with a small surface roughness of Ra = 11 nm, indicating a high packing density of atoms. This ensures bump uniformity across the sample, as well as prevents oxidation inside the In columns prior to the reflow. A series of experiments to optimize indium bump fabrication technology, including a shear test of single columns, is described. A reliable, repeatable, simple, and quick approach was developed with the pre-etching of indium columns in a 10% HCl solution preceded by annealing at 120 °C in N2.

We have developed a tunable semiconductor double-chirped mirror with high negative dispersion grown by molecular beam epitaxy. The simplified numerical plane-wave reflection transfer method was applied to design the dispersive mirror structure. The multilayer stack was grown of AlAs/GaAs materials and capped by an SiNx antireflective layer. The group delay dispersion as well as reflectivity characteristic were continuously tunable across the mirror surface from 1080 to 1000 nm. Within this range, the negative value of the dispersion changed from -3850±100 fs2 over the 6 nm band around 1080 nm to -2200±100 fs2 over 13 nm around 1000 nm with the reflectivity from the range of 99.0÷99.2%. The mirror performance was tested in a diode-pumped femtosecond Yb:KYW oscillator.

We report on the development of semiconductor double-chirped mirrors with the group delay dispersion of −3,800 ± 100 fs2 in the wavelength range between 1,058 ÷ 1,064 nm and reflectivity of 99.1 %. The simplified plane-wave reflection transfer method was used to design the mirror multilayer stack. The mirror contains an epitaxial AlAs/GaAs structure topped with a SiNx antireflective layer.

Genetic algorithm was applied for optimization of dispersion properties in semiconductor Bragg reflectors for applications in femtosecond lasers. Broadband, large negative group-delay dispersion was achieved in the optimized design: The group-delay dispersion (GDD) as large as $$-3500\,\hbox {fs}^{2}$$ was theoretically obtained over a 10-nm bandwidth. The designed structure was manufactured and tested, providing GDD $$-3320\,\hbox {fs}^{2}$$ over a 7-nm bandwidth. The mirror performance was verified in semiconductor structures grown with molecular beam epitaxy. The mirror was tested in a passively mode-locked Yb:KYW laser.

We investigate selected problems of the molecular beam epitaxy (MBE) technology of fabrication of semiconductor saturable absorbers, which are the main parts of broadband saturable absorber mirrors. These mirrors are designed for mode locking of solid-state lasers emitting in 808 nm band. We analyzed growth conditions during the MBE processes of fabrication of test structures containing the central part of the device with a quantum well (QW). Two main parameters were changed in the processes: the growth temperature of InGaAs/GaAs QW and the arsenic to metals flux ratio. Four types of growth conditions were applied during the test processes. Grown structures were tested by optical methods: photoreflectance and pump–probe spectroscopy (pump–probe measurements and saturation measurements). Obtained results enabled us to establish a correspondence between applied growth conditions and main optical parameters of the absorbers.

At low temperatures, ionized impurities are the dominant scattering mechanism limiting carrier mobilities in most semiconductors. Calculations of ionized impurity scattering have usually been based on the assumption that the ions scatter independently of one another. The purpose of this paper is to investigate the method of mobility calculation in which the carrier spectrum is found by solving the neutrality equation numerically. A development of the method, which allows calculation of the temperature dependent mobility spectrum of all carriers used in the neutrality equation for the GaAs/GaAs sample is presented. In order to explain the transport properties the following topics are discussed: • Theoretical calculation of the n-type GaAs transport parameters. • Comparison between measured and calculated values of the conductivity and Hall concentration, resistivity, conductivity and Hall mobility. • The values of conductivity mobility for each carrier transport component. • Application of the method for characterization of n-GaAs on SI GaAs MBE epi-layers. The new method allows for determination of the carrier mobility spectrum and is applied to GaAs/SI-GaAs layers in which the Hall voltage is magnetic field dependent.

The paper is a study of the microstructure of as grown semiconducting and semi-insulating GaAs crystals, as well as of fine structural changes induced in both materials by the implantation with a 5×1014 cm−2 dose of 3 MeV/amu nitrogen ions. X-ray measurements were carried out by means of a high-resolution diffractometer. The rocking curves of two as-grown GaAs samples studied are symmetrical. The rocking curve measured for the implanted semi-insulating crystal is broadened, while that for the implanted semiconducting crystal reveals a diffused subsidiary peak on the low angle side of the main maximum, indicating the presence of tensile stresses in the damaged layer at a depth of the mean ion range. The mathematical analysis of the reciprocal space maps gives a quantitative description of the experimental results.

At low temperatures In 0.53 Ga 0.47 As samples show an increase of carrier concentration, which can be explained in terms of a two carriers transport model. This type of problem exists since the beginning of the semiconductor era, dating back to monocrystalline germanium. We propose that in all the investigated layers, there are X atoms or charged dislocations in the region of the first monolayers, which are built in during epitaxial growth. The layers were intentionally undoped. They form an impurity band in which low mobility carriers dominate over the localised electron scattering due to the s–d exchange interaction. These carriers do not freeze out at liquid helium temperature and give rise to two transport media for electrons; a conduction band at higher temperatures and an impurity band at lower temperatures. The electron which fall down onto the previously ionised X atoms, then move by thermally activated hopping. We show that the two carriers model for In 0.53 Ga 0.47 As epitaxial layers are confirmed by the carrier concentration–temperature, carrier concentration–magnetic field, resistivity–magnetic field behaviour, and also by YKA theory also. The differences between the two transport models are so distinctive that observed phenomena may exist. This paper presents experimental results, which constitute comprehensive evidence for the complicated structure of the semiconductor epitaxial layers on the sample of n -type In 0.53 Ga 0.47 As/InP layer with n =2.2×10 15 /cm 3 .

The design of the vertical cavity surface emitting lasers (VCSELs) needs proper tuning of many different optical parameters of those structures. So, the optimisation of the VCSELs requires deep understanding of optical processes occurring in the active regions of such lasers. In a series of MBE processes, active regions of VCSELs as well as the whole VCSELs were grown. The active regions of the VCSEL structures were designed for λ=1000 nm and 980 nm emission. They consisted of a pair of distributed Bragg reflectors (DBRs) composed of AlAs and GaAs quarter wavelength layers and a cavity made of GaAs. The cavities contained one or several quantum wells (QWs) made of In 0.2 Ga 0.8 As. To optimise the optical characteristics of the active regions, several experimental methods have been applied. The Bragg reflectors and the whole microcavities were investigated by optical reflectivity. For selective excitation of a QW in a cavity active layer, a Ti–sapphire tuneable laser has been used. The fine tuning between the QW emission and the cavity Fabry–Perot resonance has been investigated by photoluminescence at varying temperatures of the sample. For monitoring the temporal evolution of the luminescence from the active region of the laser, time-resolved spectroscopy has been employed. The combination of many methods of optical investigations enabled a comprehensive characterisation and as a result an optimisation of the whole laser structure.

The effect of treatment at up to 1270 K under hydrostatic argon pressure, up to 1.2 GPa, on strain relaxation of AlGaAs layers was investigated by X-ray diffraction and related methods. The 1.5 μm thick AlGaAs layers weregrown by molecular beam epitaxy method on 001 oriented semi-insulating GaAs substrate at 950 K. An increase in intensity of X-ray diffuse scattering, originating from hydrostatic pressure-induced misfit dislocations, was observed for all treated samples. For the samples treated at 920 K during 1 h under 0.6 GPa, the diffuse scattering was confined to the [110] crystallographic direction perpendicular to the direction of dislocations. For the samples treated at 1.2 GPa at the same temperature and time conditions as for 0.6G Pa, a different behaviour is observed, namely the diffuse scattering extends along all azimuthal directions, indicating that dislocations are created in both [110] and [110] directions. The change of strain after the treatment was most pronounced for the samples treated at 1.2 GPa for 1 h at 920 K.

Molecular beam epitaxy has been used to grow epitaxial InAs onto (0 0 1) oriented SI–GaAs, at different substrate temperatures T s =(440–506 °C) and different V/III flux ratios. No influence of growth rate on the microstructure of the layers has been detected. Transport properties of the layers have been investigated by Hall effect measurements under a magnetic field of 0.6 T, at temperatures from 3.5 to 300 K. InAs samples exhibited a characteristic maximum of Hall coefficient (minimum of Hall concentration) at temperatures of about 60 K, which is not typical for semiconductors. We propose a model for interpreting this behaviour, which is extended to other nominally undoped samples.

The optimized nonuniform growth process was used to achieve spatially dependent reflectivity and dispersions characteristics in a highly dispersive semiconductor mirror. The mirror, together with a semiconductor saturable absorber mirror (SESAM), was used to demonstrate a tunable femtosecond Yb:KYW oscillator. In the passive modelocking regime the laser could be continuously tuned over 3.5 nm spectral band around 1032 nm with high resolution, maintaining the average output power above 140 mW.

The intra-pulse measurements of the beam steering in an AlGaAs/GaAs quantum cascade laser are presented in this paper. The experimental results are explained by a two-mode theoretical model. The near field of the laser radiation is calculated according to the effective index method and transposed to the far field numerically according to Huygens principle. The maximal observed value of deflection of the beam has been found to be \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$17^{\circ }$$\end{document}17∘. For supply currents in the range from 1.6 to 2.4 times the threshold the beam steering occurs only on one side of the resonator axis, and stays is the same for all current values. For higher supply current, it occurs alternately on both sides and exhibits a bistability. The time period of the beam direction change has been found to be about 40 ns for the lowest current and was decreasing with the current increase to about 20 ns.

We discuss some problems of molecular beam technology (MBE) technology of planar microcavities based on GaAs, AlGaAs and InGaAs compounds. This technology needs specific methods of in situ control and postgrowth characterization. One of the crucial problems is that of controlling the substrate temperature and the growth rate with very high accuracy. We demonstrate the usefulness of substrate temperature oscillations observed by infrared pyrometry for both the temperature and the growth rate control. For studying the perfection of layers and interfaces the cross-sectional transmission electron microscopy has been used. To optimize the optical characteristics of the microcavities, several experimental methods have been applied. The Bragg reflectors were investigated by optical reflectivity. For selective excitation of a quantum well (QW) in a cavity active layer, the Ti-sapphire tuneable laser have been used. The fine tuning between the QW emission and the cavity Fabry–Perot resonance has been investigated by photoluminescence for varying temperature of the sample.

The performance of In x Ga 1~x As detectors operating in the 2}3.4 lm spectral range and temperature of 300 K has been analyzed theoretically as a function of wavelength, band gap and doping level with special emphasis on 2}2.5 lm and 3}3.5 lm atmospheric window devices. The calculations show that the dominant generation}recombination mechanism in p-type, intrinsic and in a lightly doped n-type InGaAs is the spin split-o! band Auger process (AS). Since the AS generation increases with the square of the hole concentration, the minimum thermal generation and the best performance can be obtained using moderately doped n-type material as the absorber region of a photovoltaic device. In principle, the ultimate performance can be achieved in the optimized homojunction devices with relatively thick n-type absorber region forming n}p junction with a thin p-type material. N-type doping of absorber region of InGaAs photodiodes at 300 K changes from 1]1014 to 5.2]1015 cm~3 for devices optimized for operation at 2 and 3.4 lm wavelength, respectively. ( 2000 Elsevier Science B.V. All rights reserved.

(a) Institute of Physics, Polish Academy of Sciences, Al. Lotniko´w 32/46,PL-02-668 Warsaw, Poland(b) Institute of Experimental Physics, Warsaw University, Ul. Hoz˙a 69,PL-00-681 Warsaw, Poland(c) Institute of Electron Technology, Al. Lotniko´w 32/46, PL-02-668 Warsaw, Poland(Received October 1, 1998)An analysis of extended defects generated during annealing by pulsed excimer laser radiation in sili-con crystals implanted with Ge ions is presented. The investigation was performed by means of twocomplementary methods: the interference-polarizing microscopy and the Lang X-ray transmissiontopography. The existence of extended defects was revealed. It has been stated that the distributionof these defects depends on the distribution of the power density in the laser beam cross-section.

Mechanism of the optical detection of cyclotron resonance via emission from 2D electron gas in modulation doped quantum wells and in high electron mobility structures of GaAs/AIGaAs is discussed based on the results of time-resolved optical detection of cyclotron resonance. An important role of impact ionization processes is demonstrated. We also show that microwave radiation destroys emission enhancement at the Fermi level and the relevant mechanism is proposed.

The nature of a small “precursor” of resonance which appears in front of the main resonance peak in the current–voltage characteristic of resonant-tunnelling devices based on GaAs/AlGaAs double-barrier heterostructures is studied. The competition between the precursor and main-peak current is examined within the temperature range 2–400 K and under a magnetic field up to 13 T. The precursor is interpreted as the contribution to resonant tunnelling of ballistic electrons injected from a three-dimensional electron gas in the emitter region. Instead, the main resonance peak is due to the electron injection from a two-dimensional electron gas in a triangular well formed under bias in the emitter spacer layer.

A new algorithm of the analysis of the electrical conduction in the layers forming a semiconductor structure has been described. In the algorithm, in contrast to earlier approaches, the mobility spectrum technique has been applied to the sheet conductivity tensor. The standard carriers parameters have been estimated from the tensor components in the high and low magnetic field limits. The proposed method has been illustrated by the analysis of results of the electrical conduction measurements versus magnetic field performed up to 1.6 T at 77 K in a molecular beam epitaxial (MBE) grown GaAs:Si structure. The sample was an MBE GaAs:Si layer grown on a buffer epilayer. As a result of the analysis, the mobility spectra and the standard parameters describing carriers in different layers have been found.

Quantum cascade lasers (QCL’s) have proven their usefulness as light sources in many applications, like remote gas sensing, molecular spectroscopy or free-space communication. In most cases the high-quality low-divergence beam is desired. This work presents the theoretical analysis of QCL’s beam divergence. The electromagnetic field in the resonator is calculated according to effective index method. Theoretical results are compared with measurements.

The paper presents results of experimental investigations of spatial distribution of radiation emitted by quantum cascade lasers. Measurements have been performed by means of a unique goniometric profilometer specially de- signed for the large angle laser beams. The advantages and limitations of the set-up and the applied experimental method are discussed. The obtained results have enabled the analysis of dependence of geometry of the beam on the geometry of the laser structure and on the mount method of the laser chips. The angular divergence of the beams has also been tested as a function of laser power supply.

A reflection high-energy electron diffraction (RHEED) experiment has been carried out to show the evidence of surface resonance effects when resonance diffraction conditions are satisfied during MBE growth. First the rocking curves of RHEED intensity from an atomically clean Si(111) surface were measured before Si deposition. Then RHEED intensity oscillation curves were recorded at several angles of incidence during the homoepitaxy of Si in the MBE process. The results of those combined measurements show that there exists such an angle of incidence (corresponding to the resonance diffraction conditions on a clean surface) that many characteristic effects of the surface resonance occur. It has been demonstrated that at the resonance conditions the modulation depth of the intensity oscillations attains its maximum. Certain characteristic features of this phenomenon are analysed and a possible application to the control of the MBE process is mentioned.

There is a considerable interest in type-II GaSb/InAs superlattice system due to several modern applications including infrared detectors. In these studies X-ray photoelectron spectroscopy (XPS) and spectroscopic ellipsometry (SE) have been used for extensive characterization of the surface and interface of GaSb/InAs superlattice. Application of XPS and SE techniques provides precise information from topmost layers of structure and allows excluding presence of GaAs-type interfaces in GaSb/InAs superlattices. It means that Sb-for-As anion exchange does not exist during the molecular beam epitaxial growth of superlattice structures. Simultaneously, these results indicate that InSb-type or GaInSb-type interfaces have been detected in the structures studied.

X-ray diffraction topography (Bragg diffraction) and X-ray rocking curve measurements were used to study the perfection and structural properties of ZnTe epitaxial layers ohs the CdTe and GaAs substrates. ZnTe epitaxial 1ayers on CdTe were grown by MBE method b y using a machine made in the Institute of Physics of the Pofish Academy of Sciences. The ZnTe layers on GaAs were produced on the other, factory-made MBE system. The comparison between the X-ray topographical images of the substrate and epitaxial layer shows that imperfections on the substrate surface cause imperfections in the epitaxial layer. The results of double-crystal diffractometry measurements show that the perfection of the layer on the GaAs substrate is higher than that on the CdTe. The presence of microtwining in the ZnTe layer on the CdTe substrate was confirmed by RHEED measurements. The X-ray standing wave fluorescent spectra were also measured for the samples. PACS numbers: 61.10.—i, 61.14.Hg, 68.55.—a

Using complementary x-ray and electron-optical methods, a ZnSe(Co) crystal with natural face was investigated. X-ray diffraction methods such as double-crystal x-ray reflection topography, double-crystal diffractometry for rocking curve measurements, precise lattice constants measurements by the Bond technique were used for crystal structure characterization and x-ray fluorescence method for studies of chemical composition along the crystal. The scanning electron microscopic image of the crystal surface and reflection diffraction of the high energy electrons enriched the crystal structure characterization

The operation in the 1020 nm wavelength range of strained-layer InGaAs/GaAs separate-confinement-heterostucture lasers grown by molecular beam epitaxy is reported. The active region is formed by a single 80 A thick InGaAs quantum well with an indium content of 25%, which is close to critical parameters. This paper provides the operating characteristics of broad-area uncoated Fabry–Perot structures with cavities of 700 μm length measured in the pulsed regime. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 29: 75–77, 2001.

Molecular beam epitaxy has been used to grow thick epitaxial InAs onto (001) oriented SI-GaAs, under a wide range of substrate temperatures ( T s =440–506°C) and different V/III flux ratios (ϕAs 4 /ϕIn). Microstructure of epilayers was examined by high-resolution X-ray diffractometry. It has been found that full width at half maximum (FWHM) of the (004) rocking curves could be as low as about 120 arcsec when the layers were grown at T s =506°C and (ϕAs 4 /ϕIn)≈6. Transport properties of the layers have been investigated by Hall effect measurements in the magnetic field up to 1.5 T at temperatures from 3.5 to 300 K. It has been found that the properties of InAs are greatly influenced by the growth conditions, especially by substrate temperature during epitaxial process. Additionally all InAs layers exhibited characteristic maximum of Hall coefficient at temperatures of about 60 K, which is not typical for semiconductors. It is shown that assumption of existence of two additional levels allow to fit all transport characteristics.

Design and fabrication of saturable Bragg reflectors (SBRs) by molecular beam epitaxy (MBE) is presented. Grown structures consisted of AlAs/GaAs quarter-wave layers with low-temperature InGaAs/GaAs quantum wells (LT QWs) as saturable absorber layers. Special emphasis is put on methodology of wavelength tailoring of distributed Bragg reflectors and on MBE technology of growing the quantum wells with the recombination time of excitons of the order of tens ps. Application of different methods of characterization of LT QWs and SBRs for testing and optimizing the MBE process is discussed.© (2006) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The technology of GaAs MBE layers for K-band Gunn diodes is described in the paper along with the method of diode structure preparation. Chips were assembled directly in a microwave generator. The design of measurement circuit and microwave generator, as well as results of experiments are presented.

The operation of InGaAs/GaAs SCH SQW lasers emitting at the wavelength 1.02-1.03 /spl mu/m, fabricated by MBE technology, is reported. Longer wavelength of emission was achieved by applying high indium content in the active region. The paper presents characteristics of fabricated structures measured at room temperature (T=300 K) under pulsed operation. The results are promising and give hope for fabricating structures emitting at 1.06 /spl mu/m, which in some applications could replace diode pumped Nd:YAG lasers.

Strained layer InGaAs/GaAs SCH SQW (Separate Confinement Heterostructure Single Quantum Well) lasers were grown by Molecular Beam Epitaxy (MBE). Highly reliable CW (continuous wave) 980 nm, broad contact, pump lasers were fabricated in stripe geometry using Schottky isolation. Threshold current densities of the order of J/sub th//spl ap/280 A/cm/sup 2/ (for a resonator length L=700 /spl mu/m) and differential efficiency /spl eta/=0.4 W/A (41%) were obtained. The wall-plug efficiency was 38%. Theoretical estimations of these quantities obtained by numerical modelling of devices were J/sub th/=210 A/cm and /spl eta/=0.47 W/A respectively.

The performance of uncooled InxGa1-xAs photovoltaic devices operating in the 2-3.6 micrometers spectral range has been studied both theoretically and experimentally. Various multilayer homo- and heterojunction devices have been considered. Band-to-band Auger processes were taken into account as the dominant mechanisms of thermal generation and recombination. Calculations show that the best performance can be obtained in devices with lightly doped n-type absorber region as a result of the significant role of Auger S (spin-off band) process. The optimized heterostructures with near intrinsic n-type narrow gap InGaAs absorber were grown using molecular beam epitaxy. The performance of the present InGaAs devices remains significantly below theoretical limits. Better agreement can be observed for devices with longer cutoff wavelength as the result of increasing role of fundamental limitations and improved quality of materials with x approximately equal to 1. Improvement of performance by almost an order of magnitude has been achieved by the use of monolithic optical immersion. This has been accomplished by growth of the InGaAs heterostructures on thick SI GaAs substrates and by formation of the immersion lenses directly in the substrate. These devices are expected to find important applications in infrared systems which require better performance than existing uncooled detectors.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Spontaneous emission control has been achieved in InxGa1-xAs/GaAs planar microcavities with DBR reflectors. The room temperature emission in λ-sized cavities is enhanced compared to its free space value whilst in λ/2-sized cavities suppression of spontaneous emission is observed. The characteristics of spontaneous emission in microcavities depend on the wavelength difference between the emitter and the cavity resonance. It has been shown that ideal tuning of the cavity can be achieved by adjusting the sample temperature. In general, the observed trends are in agreement with theoretical predictions. These changes in the spontaneous emission process directly effect VCSEL properties. An increased coupling efficiency of spontaneous emission into the lasing mode is observed in VCSELs with λ-sized cavities.

The structure of InGaAs (InAs) layers grown on InP (001) and GaAs (001) surfaces by Molecular Beam Epitaxy was studied by high-resolution x-ray diffractometry. The reciprocal lattice mapping and the rocking curve technique were used to determine distribution of misfit dislocations in the layers. Directional dependence of dislocation density in InGaAs strained layers grown at 2D growth mode was observed. It was found that anisotropic distribution of dislocations in the InGaAs layers resulted from development via bending in the interface plane of dislocations present in the InP substrate. Simultaneously, homogeneous distribution of dislocations in relaxed InAs layers grown on InP as well as GaAs substrates has been detected. At the initial stage these epitaxial layers were grown to 3D island mode. The reciprocal lattice maps confirm that coalescence of islands during the epitaxy generates dislocations, which in turn homogeneously distribute in the layer. It seems that the growth mode rather than lattice mismatch determines density of dislocations in InAs epitaxial layers grown on InP and GaAs substrates. However, lattice mismatch influences relaxation process in lattice-mismatched layers. Transport properties of relaxed InAs layers strongly depend on growth temperature.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We present comprehensive numerical modeling of graded-index separate-confinement-heterostructure single-quantum well (GRIN SCH SQW) lasers. In particular, we present for the first time a modified drift-diffusion model of the laser, which correctly takes into account quantum nature of carriers in the active region. The drift-diffusion equations are solved self- consistently together with Schrodinger and Poisson equation. The analysis is carried out for the general case of MQW active region. We employ our model to predict the behavior of the devices fabricated by molecular beam epitaxy (MBE) technique. The broad contact, test lasers produced in our laboratory exhibited threshold current density Jth equals 350 A/cm2, intrinsic mode loses as low as 7 cm-1 and internal quantum efficiency near unity. External quantum efficiency above 80% was achieved. The emitted power per uncoated facet just before degradation was equal to 5 W for pulsed operation with 0.1% filing factor and 140 mW for cw operation. We also discuss the development of the technology in terms of growth temperature and V/III beam fluxes ratio optimization.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We have measured the photoreflectance (PR) spectra at room and liquid nitrogen temperatures of two MBE grown GaAs/AlGaAs structures. The first one is HEMT type system with buried 10 periods of 2.5 micrometers GaAs/2.5nm AlGaAs superlattice. Oscillations-like signal associated with this SL have been observed and detailed analyzed. The second investigated structure is the sequence of 10 different quantum wells. Transitions in almost all wells and those associated with above barrier states have been observed. The experimental transitions are well described in terms of envelope function model.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We demonstrate a semiconductor double-chirped mirror consisting of an AlAs/GaAs multilayer stack grown by molecular beam epitaxy. The mirror has a high negative group velocity dispersion of −2450 ± 100 fs2 and a reflectivity exceeding 98.9% over the spectral range spanning ±4 nm around 1035 nm. When used to compensate the cavity dispersion in a diode-pumped femtosecond Yb:KY(WO4)2 oscillator, at 490 mW of the absorbed pump power, the laser delivered 110 mW in pulses of 240 fs duration.

Journal of applied physics 113, 064302 (2013). doi:10.1063/1.4790712, Published by American Institute of Physics, Melville, NY

A new method to calculate the near field of widely divergent laser beams based on a given far field is proposed. It is assumed that the field of radiation consists of several transversal modes and the far field is determined by the Huygens principle. The idea consists in employing the least squares method to find a minimum of the difference between the measured far field and the far field calculated under the assumption that is consists of several transversal modes with assumed weights. To find this minimum the Levenberg–Marquardt algorithm is used. Thus the problem is dealt beyond the paraxial approximation. The method is illustrated by its results for experimental mid-infrared quantum cascade laser beams and for the beams obtained by simulations.

InxGa1—xAs/GaAs heterostructures of various thicknesses of InxGa1—xAs layer and various indium contents were grown by means of molecular beam epitaxy on a (100)-oriented GaAs semi-insulating substrate in a Riber 32P set-up. Structural perfection of the heterostructures were determined using transmission electron microscopy and X-ray diffractometry. The purpose of this paper is to understand how the geometry of heterostructure and the indium content in the InxGa1—xAs layer influences the lattice perfection of the heterostructure. From the wide range of thicknesses and contents only those having practical application in devices were selected. The formation of dislocations in InxGa1—xAs/GaAs heterostructures with thin InxGa1—xAs layers, InxGa1—xAs multilayers grown on GaAs substrates and in index-graded InxGa1—xAs (x = 0.01 to 0.53) layers was studied. Conditions of the formation of defects were discussed. A mechanism of dislocation formation in index-graded InxGa1—xAs layers was proposed.