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We have investigated strain‐induced lateral quantum confinement in a GaAs quantum well, as well as strain propagation along the material growth direction. The lateral confinement was generated by etching a grating pattern into a stressor of InGaAs which overlies a GaAs quantum well. For strain‐induced quantum well wires formed by an In0.35Ga0.65As stressor, the excitation intensity‐ and temperature‐dependent photoluminescence spectra show two well‐resolved one‐dimensional subband transitions whose splitting is 7.5±0.5 meV. We used luminescence data for multiple quantum wells, set at different distances beneath an In0.3Ga0.7As stressor, to confirm that the propagation depth of strain along the material growth direction is comparable to the width of wire stressors.

We report on the study of Si-doped GaAs/AlGaAs narrow multiquantum wells (MQWs) using the intersubband photoinduced absorption technique. For the barrier-doped MQWs, we find thatan impurity level which is ∼ 60 meV below the barrier band gap, causes a photoinduced reduction (“bleaching”) in the e1–e2 intersubband absorption. This is not observed for the MQWs doped in the well. For a Si-doped level of ∼ 2.5 ×1016 cm−3 (in the barriers), we estimate the density of the impurities causing the bleaching to be of the order of 2 ×108 cm−2 per barrier.

We have investigated the effect of a parallel electric field on the low-temperature photoluminescence from ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As/(n-type GaAs):Si quantum wells. We have studied the electric-field effect in a number of molecular-beam-epitaxy-grown ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As/GaAs quantum-well structures doped with Si in the center of the well with well widths from 40 to 190 \AA{}. We observe sharp thresholds in the quenching of luminescence from the free and bound excitons at fields near a few tens of V/cm, accompanied by a sharp increase in the current. The actual threshold is critically dependent on the well width of the sample, which is qualitatively explained by the differences in carrier mobility. The mechanism responsible for the observed effects will be shown to be due to impact ionization of the excitons by the free carriers heated in the electric field.

Polarization modulation is used to investigate the polarization dependencies in the low‐temperature photoluminescence (PL) and the photoluminescence excitation (PLE) of GaAs/AlGaAs quantum wire arrays. The modulation technique employing a photoelastic modulator is described and its implementation in the experimental setup of the PL and PLE experiments is presented. In the PL experiment the technique is used to analyze the emitted light with respect to its polarization, whereas for the PLE experiment the polarization of the exciting light is modulated, probing the polarization dependence of the absorption of the light. Since the modulation of the light is restricted to the polarization, the polarization dependence can be measured simultaneously with the PL or PLE intensity. The versatility and the sensitivity of the technique is exemplified by presenting results of polarized PL and PLE obtained on quantum wire samples grown on the vicinal (100) surface of GaAs by molecular‐beam epitaxy that show a considerable anisotropy in the linear polarization for both the PL and PLE.Polarization modulation is used to investigate the polarization dependencies in the low‐temperature photoluminescence (PL) and the photoluminescence excitation (PLE) of GaAs/AlGaAs quantum wire arrays. The modulation technique employing a photoelastic modulator is described and its implementation in the experimental setup of the PL and PLE experiments is presented. In the PL experiment the technique is used to analyze the emitted light with respect to its polarization, whereas for the PLE experiment the polarization of the exciting light is modulated, probing the polarization dependence of the absorption of the light. Since the modulation of the light is restricted to the polarization, the polarization dependence can be measured simultaneously with the PL or PLE intensity. The versatility and the sensitivity of the technique is exemplified by presenting results of polarized PL and PLE obtained on quantum wire samples grown on the vicinal (100) surface of GaAs by molecular‐beam epitaxy that show a consider...

A 45 degrees angled reactive ion etching combined with an in situ monitoring technique was used to fabricate ridge waveguide folded-cavity in-plane surface-emitting lasers. This laser structure, with two 45 degrees C angle-etched internal total-reflection mirrors and an epitaxially grown distributed Bragg reflector, is very promising for OEIC applications. Laser-structure design and laser fabrication are addressed. A continuous-wave threshold current of 8 mA, the lowest reported in the literature, was achieved on 3- mu m-wide, 350- mu m long devices. >

Using infrared (IR) photomodulation spectroscopy in lightly doped GaAs/AlGaAs multiple quantum wells (MQW), we study the changes in the e1–e2 intersubband absorption due to the interband excitations. For the barrier doped MQWs, we find that an impurity level which is ∼ 60 meV below the barrier band-gap, strongly affects both the shape and intensity of the intersubband transitions. No such effects are observed in the well-doped MQWs.

A spectroscopic study of narrow quantum wells doped with shallow acceptors is presented, employing tunable resonant laser excitation in both CW and transient mode. The picosecond transient data directly demonstrate the spectral diffusion of both localized free excitons (FE's) and bound excitons (BE's), if they are resonantly excited at sufficiently high photon energies. Similar data taken with resonant CW excitation show a sharp BE peak resonantly excited via localized excitons (LE's). allowing a precise determination of the binding energy of bound excitons. At lower photon energies sharp Raman peaks are observed and identified as shake-up two-hole processes for the acceptors, as well as LO phonon replica enhanced by localization at interface potentials. Similar resonant Raman shake-up processes are seen for the FE. The same replica processes occur in nonrcsonant luminescence, as shown by the background in the spectra.

This letter presents a study of optical phonon modes of single-crystalline orthorhombic ZnSiN2 semiconductor epitaxially deposited on r-sapphire. An epitaxial relationship for ZnSiN2 film was found from x-ray diffraction to be (0k0)ZnSiN2‖(10 12)Al2O3 and [100]ZnSiN2‖(1210)Al2O3. Six B1 optical modes were revealed in 400–1000 cm−1 range in s-polarized infrared reflectance spectra. This is consistent with the analysis of the phonon symmetry and selection rules presented. The frequencies of the transversal and longitudinal components, phonon damping, and oscillator strengths of the B1 phonons as well as high frequency dielectric constant e∞xx of the orthorhombic ZnSiN2 were determined.

We have investigated the influence of Si-N complexes on the electronic properties of GaAsN alloys. The presence of Si-N complexes is suggested by a decrease in carrier concentration, n, with increasing N-composition, observed in GaAsN: Si films but not in modulation-doped heterostructures. In addition, for GaAsN: Te (GaAsN:Si), n increases substantially (minimally) with annealing-T, suggesting a competition between annealing-induced Si-N complex formation and a reduced concentration of N-related traps. Since Si-N complex formation is enhanced for GaAsN: Si growth with the (2x4) reconstruction, which has limited group V sites for As-N exchange, the (Si-N)(As) interstitial pair is identified as the dominant Si-N complex. (C) 2009 American Institute of Physics. (DOI: 10.1063/1.3198207)

In this study we present photoluminescence decay measurements of free-exciton (FE) and bound-exciton (BE) recombination in doped GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As multiple quantum wells (QW's). It is found that the FE decay time is reduced in the doped QW's compared with similar undoped samples. For a sample with a QW width of 80 \AA{}, we obtain a capture rate of 0.12 ${\mathrm{cm}}^{2}$ ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$ from the FE to the BE. The low-temperature decay time of the BE is slightly longer than for the FE, with BE decay times varying from 300 to 600 ps for well widths in the range of 50 to 150 \AA{}, respectively. At temperatures above 10 K, we find a similar decay time for the FE and BE recombination. We conclude that the FE and BE are in thermal interaction and, based on the assumption of thermal equilibrium between the two states, we present a simple model to explain the temperature dependence of the photoluminescence data.

The electronic structure of one-sided modulation-doped n-channel ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As/GaAs heterostructures has been studied by photoluminescence excitation spectroscopy in samples with a narrow (\ensuremath{\approxeq}500 \AA{}) active GaAs region. The excited two-dimensional (2D) electron states are observed optically at 2 K, and 2D hole quantization is also found to be important for the structure investigated. Theoretical calculations including exciton effects show good agreement with the experimental data.

The radiative recombination of two-dimensional (2D) carriers in an n-type-channel modulation-doped GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As heterojunction has been studied with time-resolved photoluminescence (PL). Two emission bands related to the recombination of 2D electrons, the so-called H band 1 (HB1) and H band 2 (HB2), are observed in PL. Their spectral shape and position are strongly dependent on the sample and the experimental conditions, and are, e.g., found to shift within a large photon-energy range with the excitation intensity. We have in this study measured the decay time of these PL bands as a function of recombination photon energy, under different experimental conditions. We find that the measured decay times of both the HB1 and HB2 emissions are strongly dependent on the detection photon energy. The decay times are found to increase with decreasing photon energy, in the range 1--100 ns for HB1, and 100 ns to 10 \ensuremath{\mu}s for HB2. This increase is explained as due to a spatial separation between the recombining electron and hole. The results are consistent with a recombination process involving 2D electrons, confined in the interface notch, and holes either from the valence band (HB1) or from neutral acceptors (HB2) in the active GaAs layer. We further show that the band bending in the active GaAs region influences the observed decay times of the HB2 emission, while the HB1 emission is almost unaffected.

The radiative recombination processes involving the 2-dimensional (2D) carriers at the interface of a GaAs/AlGaAs heterostructure have been investigated by the means of different spectroscopic methods. The results obtained from photoluminescence (PL) measurements perturbed by an electric field are consistent with a model proposed earlier. Furthermore, important information about the electronic structure of the 2D electrons in the notch potential is derived from PL excitation measurements, in which the excited state of the 2D electron has been observed at lowest temperatures for the first time.

Undoped GaAs/AlGaAs quantum wells (QWs) with thicknesses in the range, 40A

We have examined the effect of the confinement on the electronic structure of defect states in GaAs/AlGaAs quantum wells (QWs) by means of selective photoluminescence (SPL), excitation spectroscopy, resonant Raman scattering (RRS) and related methods. The energy levels for confined acceptors have been investigated by monitoring the two hole transitions (THTs) in SPL experiments and RRS measurements via the bound exciton. Confinement effects resulting from both the width of the QW and the acceptor position in the QW have been studied. A corresponding study on donor states is initiated and the first results on two electron transitions will be presented. Also satellite emissions associated with the free exciton (FE) have been observed in undoped QWs. The behaviour of these satellites is in many ways similar to the extrinsic THTs and are interpreted as the corresponding intrinsic THTs caused by the interaction between a FE state and an adjacent "free" hole. The prerequisite for such an interaction is an overlap of the involved wave functions, which is explained in terms of localization of these states due to interface roughness.

An introduction to the operation of quantum-dot cellular automata is presented, along with recent experimental results. Quantum-dot cellular automata (QCA) is a transistorless computation paradigm that addresses the issues of device density and interconnection. The basic building blocks of the QCA architecture, such as AND, OR, and NOT are presented. The experimental device is a four-dot QCA cell with two electrometers. The dots are metal islands, which are coupled by capacitors and tunnel junctions. An improved design of the cell is presented in which all four dots of the cell are coupled by tunnel junctions. The operation of this basic cell is confirmed by the externally controlled polarization change of the cell.

We report on the growth of ZnSnP2 on GaAs(100) substrates by gas source molecular beam epitaxy. Samples were grown in the temperature range of 300–360 °C. A small change in the Sn/Zn flux ratio at constant substrate temperature was found to result in a transition from a lattice mismatched, Δa/a∼0.4%–0.7%, disordered crystal structure to a lattice matched, ordered chalcopyrite structure. Infrared reflectance and Raman measurements were used to monitor this phase transition. Formation of the two different crystal modifications is discussed in terms of vapor–solid and vapor–liquid–solid growth modes.

Near-field photoluminescence (NPL) spectroscopy with a spatial resolution below the light diffraction limit was used to study the optical fields of whispering-gallery modes (WGMs) in GaAs and AlGaAs microdisks (radii $R=1--3\text{ }\ensuremath{\mu}\text{m}$ and quality factors $Q\ensuremath{\sim}5\ifmmode\times\else\texttimes\fi{}{10}^{3}$) containing InAs quantum dots (QDs). WGMs with azimuthal mode numbers $m=10--36$ and radial mode numbers $l=1--3$, together with low-$Q$ Fabry-P\'erot modes and other non-WGMs, have been resolved in NPL spectra in the range of $1.1--1.3\text{ }\ensuremath{\mu}\text{m}$. We found that spectrally resolved NPL intensity images of the WGMs reveal $m$ azimuthal maxima around the disk circumference, which correspond to the period of the field amplitude. Using finite-difference-time-domain (FDTD) calculations, we show that the amplitude imaging arises from the interference between the WGMs and a background field formed by low-$Q$ modes. We show further that such interference reflects the inhomogeneity of the radiation decay of the QD ensemble in the MD. We demonstrate a direct measurement of WGM quantum numbers in microdisks by using NPL imaging, which shows good agreement with FDTD calculations.

The radiative recombination processes of two-dimensional (2D) carriers have been studied for n-channel AlGaAs/GaAs heterojunctions with different doping levels. The recombination involving the 2D carriers confined on the GaAs side of the interface notch gives rise to two different photoluminescence (PL) bands, the so-called H-bands. A considerable variation of these bands in PL spectra is observed concerning shape, broadening, energy position and decay times. This variation depends on the experimental conditions, such as the temperature, intensity and photon energy of the excitation, but also on the design of the sample. Also, the dependence on these parameters is different for the two H-bands. The results are consistent with a general model for the origin of the two H-bands in n-channel heterojunctions as due to the recombination between 2D electrons confined in the GaAs notch and holes from either the valence band or the neutral acceptors in the active GaAs layer. The observed variations are explained as due to a corresponding variation in the band bending across the active GaAs layer. The spatial separation between the holes and the electrons involved in the H-band recombination processes depends critically on this band bending.

MBE grown quantum devices for the detection of infrared light are introduced. These structures are based on photon-assisted resonant tunnelling and will have a projected tuning range of 5 to 30 mu m. Two structures are discussed: a single quantum well device with large initial population for high adsorption, and a double quantum well structure with promise of sharper detection linewidth and wider tuning range. Optical and electrical measurements of material properties are presented, and their implications on the devices discussed.

A high energy focused ion beam (Ga+, 150 keV) is used to implant and interdiffuse quantum well structures. Optical properties of wires and boxes created by this technique are evaluated by low temperature cathodoluminescence spectroscopy and imaging. We propose two different approaches to optimize the interdiffusion induced energy shift. We show the large energy shifts observed in the narrow wires and boxes (below 4000 A) are dominated by straggling effects.

We present an investigation of optical and electronic properties of a two-dimensional electron gas (2DEG) confined at a GaAs/AlGaAs interface, grown by metalorganic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE) techniques, by optical detection of cyclotron resonance (ODCR). Strong ODCR spectra structured by quantum oscillations have been observed, from which fruitful information concerning the electronic properties of the 2DEG can be obtained. This study shows the potential of ODCR as a useful and convenient (direct and contactless) probe of heterostructures.

Transitions from the ground state to excited states of the Be-acceptor confined in GaAs/AlGaAs QWs (50

Ce phenomene contraste avec les mesures de photoluminescence avec une excitation superieure a la bande interdite ou on n'observe pas la bande de la transition libre a liee. On etudie la correlation de cette bande avec les excitons libres. Dans la tentative d'explication par le mecanisme d'Auger, le trou de l'exciton libre est attire et capture par un accepteur ionise

The intersubband absorption and its photomodulation by above barrier-gap excitation in a barrier n -doped GaAs/AlGaAs multiple quantum well structure are reported. The e 1– e 2 intersubband transition is observed as an absorption band centered at 149 meV and polarized along the growth axis. The photoinduced absorption measured at temperatures below 150K consists of two parts: a bleaching band at the low energy side of the e 1– e 2 absorption band, and an absorption band on its high energy side. The photoinduced bleaching below 149 meV is assigned to a reduction in the e 1 electron population due to recombination with excess holes resulting from electrons captured by the barrier donors. The photoinduced absorption above 149 meV is probably due to the e 1: hh 1– e 2: hh 1 exciton absorption.

The transitions from the ground state, 1s, to the first excited state, 2s, of the Be acceptor confined at different positions in 96 A wide GaAs/AlxGa1−xAs quantum wells (QWs) have been studied via resonant Raman scattering (RRS) of the acceptor bound exciton (BE). Selective excitation at different resonant positions within the finite line width of the acceptor BE gives rise to an image of the distribution of acceptor transition energies corresponding to the spatial variation of the acceptor transition energies within the dopant layer. The dependence of the line width of the RRS peaks is derived from the BE binding energy and the 1s → 2s acceptor transition energy and acceptor position, z0, in the QW. The line widths are almost constant from the center to roughly z0=35 A where the line widths starts to increase dramatically.

Photoconductivity (PC) measurements have been performed on narrow GaAs AlGaAs quantum wells (QWs) using dye-laser excitation in a limited energy range: the vicinity of the excitons. The derived high resolution PC spectra are then compared with photoluminescence excitation (PLE) spectra in the same energy range for the same samples. In these PC spectra several new features appear, which to the best of our knowledge have not been reported earlier: In an undoped QW the excited 2s states in addition to the normally observed 1s ground states to each of the heavy hole- (hh) and the light hole- (lh) states of the FE can be observed. Similarly, in a doped QW a peak interpreted as the bound exciton is observed on the low energy side of the FE. The same peaks can be observed also in PLE for the samples investigated, which is a strong support for the interpretation of the observed peaks.

In this paper we review two novel types of quantum structures. The first, aimed at producing during growth quantum wire superlattices relies on the deposition of tilted superlattices. Some of the difficulties associated with the growth of tilted superlattices and the novel serpentine superlattice have been discussed and solutions proposed. The second type of quantum structures aimed at producing zero dimensional confinement structures relies on the formation of an antidot lattice. The transport properties of antidot lattices with various periodicities are presented.

GaN and AlN compounds have been proven useful in wide bandgap microelectronics and optoelectronics. Also properties of bulk GaN and AlN have been studied extensively. However, many characteristics of AlGaN/GaN superlattices are not well known. In particular, the properties of phonons have not been determined. In order to determine phonon properties, this study measured infrared reflectivity spectra on short period superlattices, which were grown by high quality molecular beam epitaxy. The superlattices consisted of 300 periods of alternating layers of GaN and AlGaN, each containing between 1 and 8 monolayers. Next, the reflectivity of each sample was measured using a Bruker IFS-66V spectrometer. From these experimental spectra the dielectric function, and hence the optical phonon properties (namely phonon frequency and phonon damping), were determined. Mapping the experimental spectra with theoretical calculations determined the longitudinal and transverse optical phonon energies present in the AlGaN/GaN superlattices. Through the examination of different AlGaN/GaN superlattice combinations, plots of phonon energies versus material composition were obtained. Furthermore, new phonons, that were not present in bulk AlN and GaN, were discovered. Finally, phonon characteristics were measured as a function of temperature, confirming that phonon energies decrease with increasing temperature.

We have investigated the evolution of molecular beam epitaxy (MBE)-grown, CdSe self-assembled quantum dots on ZnSe surfaces using microphotoluminescence techniques. Bare CdSe dots at room temperature undergo Ostwald ripening over a time scale measured in days. At the elevated temperatures maintained for MBE growth and dot formation, ripening is expected to progress much faster. Capping the dots with a thin ZnSe layer “freezes” the ripening, allowing one to sample different stages of the dot evolution and subsequent characterization. We have grown eleven samples, each with a different time interval, or growth interruption, between dot formation and capping; the growth interruption times ranging from 0 to 300 s, during which the samples were kept at 300 °C. Using microphotoluminescence spectroscopy, we have resolved the sharp emission peaks due to individual dots in each sample and, by analyzing the ensemble characteristics, have identified a new regime in the evolution of CdSe dots.

The use of near-field scanning optical microscopy (NSOM) carried out at low temperature (5K) and magnetic fields up to 10 Tesla will be described, to investigate regions of strong confinement (e.g., quantum dots) in semiconductor alloys containing nitrogen .

In this work, hexagonal defect nanocavities ("H1" and "H2") in two-dimensional photonic crystal slabs were fabricated in a half wavelength-thick semiconductor waveguide embedded with quantum dots. We characterized the cavity modes with polarization sensitive microphotoluminescence. The polarization property of the spontaneous emission was shown to be an effective approach for detecting the symmetry of the modes, from which the mode structure for an H2-cavity was experimentally verified for the first time.

Summary form only given. An InGaAs/GaAs strained-layer IPSEL (in-plane surface emitting laser) structure with two 45 degrees dry-etched mirrors and a highly reflecting bottom quarter-wavelength stack is reported. It has a record low continuous-wave (CW) threshold current at 10 mA. The laser structure consists of a conventional double-heterostructure single-quantum-well (80-AA In/sub 0.2/Ga/sub 0.8/As/100-AA GaAs) laser structure on top of a quarter-wave stack (25 pairs of 695-AA GaAs/830-AA AlAs), which serves as a distributed Bragg reflector ( approximately 99%) after 45 degrees angle etching. >

We report the formation of self‐assembling CdSe quantum dots during molecular beam epitaxial growth on ZnSe and ZnMnSe. Atomic force microscopy measurements on specimens with uncapped dots show relatively narrow dot size distributions, with typical dot diameters of 40±5 nm, and with a diameter‐to‐height ratio consistently very close to 4:1. Uncapped CdSe dots are unstable with time: their density was observed to drop by an order of magnitude in 10 days, with clear evidence of ripening observed for some dots. Photoluminescence from capped dots indicates exciton localization much stronger than in ZnCdSe/ZnSe quantum wells, due to the additional lateral confinement.

The performance of vertical-cavity lasers (VCL's) employing dielectric apertures formed by lateral oxidation or wet-etch undercutting of an AlAs layer on a common substrate are compared. Although both device types performed well, extracted optical losses from the wet-etch undercut structures exceed those of AlAs-oxide apertured lasers. The difference in performance is attributed to optical scattering losses specific to the aperture fabrication method, enhanced by loss from the larger index of refraction discontinuity of the air-gap aperture relative to the AlAs-oxide aperture.

Low-temperature near-field scanning optical microscopy was used to study the dependence of the emission spectra of single self-organized InAs on GaAs, InAs on AlAs and InP on GaInP quantum dots (QDs) on contact pressure exerted by a near-field optical fiber tip (nanoindentation). A large energy shift (up to 150 meV), broadening (up to 10 meV), and intensity increase (up to one order of magnitude) of single QD emission lines have been observed at tip compressions up to 70 nm. Ground state energy shift rates from 0.5 to 3.5 meV/nm have been measured for different aperture types (rounded and flat, metal coated and uncoated) and sizes (50--300 nm) in agreement with numerical calculations using Picus--Bir orbital-strain Hamiltonian. A reduction of the hydrostatic pressure coefficient due to a nonuniform In distribution in self-organized QDs has been observed. Anomalously strong lateral inhomogeneity of the local stress field has been observed.

The effect of nitrogen composition on structural parameters of intrinsic quantum dots (QDs) has been studied in GaAs1-yNy and InxGa1-xAs1-yNy alloys (y∼0. 015–0.03) using low-temperature near-field scanning optical microscopy (NSOM) combined with magneto-photoluminescence spectroscopy. We used measurements of the diamagnetic shift (magnetic field strength 0–10T), temperature dependent spectra (temperature range 5–300K) and near-field monochromatic images for the estimation of the size, nitrogen excess and density of QDs. The obtained values (size ∼10–30 nm, nitrogen excess ∼0.005 and density ∼100 /μm-3) suggest spontaneous formation (phase separation) of QDs. Strong lateral inhomogeniety of the QD distribution on a micron length scale was observed.

Etched pillar, bottom emitting vertical cavity surface emitting lasers (VCSELs) employing a zinc diffused and disordered spatial mode filter are fabricated and tested. The filters successfully suppress lasing of higher order transverse modes in VCSELs with diameters greater than 11 /spl mu/m, while obtaining output powers of up to 1.5 mW with threshold currents as low as 2.7 mA. Emission is entirely single mode, with mode suppression ratio greater than 25 dB up to the highest output power levels.

We present a theoretical and experimental study of optical properties on highly acceptor doped QWs. Steady state photoluminescence (PL) and PL excitation (PLE) results are compared with theoretical calculations involving exchange and correlation effects for the electron-hole system and their interaction with acceptor ions. We have studied the effects of impurity doping at levels varying from 108 up to 1013 cm-2. Excitons can still be detected at high hole concentrations above the degenerate limit. They survive due to the inefficiency of screening in the 2D system.

We describe the fabrication and operation of vertical cavity surface emitting layers by pulsed optical pumping. The structure consists of a vertical cavity resonator with SiO2/SiN distributed Bragg reflectors and a CdZnSe/ZnSe strained‐layer superlattice active region. The emission spectra rapidly narrow to full width at half‐maximum of 7 A and the emission intensity increases by over two orders of magnitude, indicating stimulated emission. Lasing is observed at thresholds of ≊44 kW/cm2 at temperatures up to 30 K with lasing wavelength near 488 nm.

The observed temperature dependence of threshold currents in InGaAs/GaAs quantum‐well ridge‐waveguide lasers is modeled. This method incorporates both experimental data and theoretical gain calculations. The results show that lateral leakage currents must be included in the ridge‐waveguide laser models. Based on the same model, the temperature‐dependent modulation characteristics for InGaAs/GaAs quantum‐well ridge‐waveguide lasers are also investigated.

Strong changes of the Raman intensity induced by the martensitic transition in spontaneously ordered ${\mathrm{GaInP}}_{2}$ alloys are explained by the triggering of the atom positions between unrelaxed (zinc-blende bond lengths) and relaxed $({\mathrm{CuPt}}_{B}$ bond lengths) arrangements. We show that these changes reflect a strong dependence of the optical-phonon properties and Raman selection rules of ${\mathrm{CuPt}}_{B}$-ordered ${\mathrm{GaInP}}_{2}$ on bond relaxation. Using analysis of the experimental spectra available in the literature we demonstrate that the relaxed and unrelaxed martensitic states can be detected by exciting different crystallographic planes. A strong effect of antiphase boundaries on the Raman spectra of spontaneously ordered ${\mathrm{GaInP}}_{2}$ is revealed.

We present results obtained using low temperature near-field scanning optical microscopy for the measurements of Zeeman splitting and the diamagnetic shift of single self-organized InAs/AlAs, InAs/GaAs and InP/GaInP quantum dots. The measurements allow us to relate the bimodal size distribution of InAs dots with variations in In content. For single InP QDs we observed a strong circular polarization at zero magnetic field accompanied with a negative energy shift, suggesting that strong internal magnetic fields exist in these QDs.

We report on the optical characterization of the strained InGaAs/GaAs quantum dots (QDs). The temperature dependence of the photoluminescence (PL) indicates that the onset energy of the thermal quenching in ∼20‐nm‐diam QDs is enhanced by a factor of ∼2 as compared to a quantum well (QW), due to the additional confinement. At low temperature, an increased carrier lifetime is observed for the QDs as compared to a reference QW (880 vs 330 ps). The carrier lifetime in the QDs was found to be independent of the temperature for T