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Continuous-wave operation near 1.3 /spl mu/m or a diode laser based on self-organized quantum dots (QD's) on a GaAs substrate is demonstrated. Multiple stacking of InAs QD planes covered by thin InGaAs layers allows us to prevent gain saturation and achieve long-wavelength lasing with low threshold current density (90-105 A/cm/sup 2/) and high output power (2.7 W) at 17/spl deg/C heatsink temperature. It is thus confirmed that QD lasers of this kind are potential candidates to substitute InP-based lasers in optical fiber systems.

Atomic force microscopy (AFM) of cleaved facets of ZnSe-based lasers with various active region designs is reported. Different AFM probe friction on the materials forming the laser structures are exploited for imaging their basic layers. Unlike ZnMgSSe-based lasers, the cleaved surface of cladding layers in BeMgZnSe-based structures is atomically flat, which is attributed to hardening of the II–VI materials by Be incorporation. Nanometer-high steps and undulations are observed at the laser heterointerfaces on cleaved facets. The shape and height of such topographic singularities located in the vicinity of a (Zn,Cd)Se quantum well active region depend on the strain distribution in the laser waveguide.

The current dependence of the optical gain in lasers based on self-organized InGaAs quantum dots in a AlGaAs/GaAs matrix is investigated experimentally. A transition from lasing via the ground state of quantum dots to lasing via an excited state is observed. The saturated gain in the latter case is approximately four times greater than for the ground state. This result is attributable to the fourfold degeneracy of the excited level of quantum dots. The effect of the density of the quantum-dot array on the threshold characteristics is investigated. A lower-density array of dots is characterized by a lower threshold current density in the low-loss regime, because the transmission current is lower, while dense quantum-dot arrays characterized by a high saturated gain are preferable at high threshold gains.

It is shown that an array of two-dimensional islands is formed during the growth of ultrathin (∼1.5 monolayers) InSb layers on a GaSb (100) surface by molecular beam epitaxy. After the deposition of several InSb layers separated by narrow barriers, islands of subsequent rows are formed on top of islands of the first row (vertical correlation effect). The formation of islands is confirmed by analysis of the photoluminescence spectra.

The photoconductivity of a two-dimensional electron gas in the far IR range in a quantizing magnetic field is investigated for samples in Corbino geometry, which eliminates transport by edge states. It is shown that the photoelectric effect is more than simply the bolometric response of the system, acquiring a component induced by the direct involvement of photoexcited carriers in low-energy scattering processes.

An analytic expression for the shape function for homogeneous broadening of the emission spectra of semiconductor heterostructure lasers is obtained on the basis of simple expressions from the theory of the superradiance of two-level systems. Good agreement between the theory and experimental data is achieved for an InGaAs/GaAs quantum-well heterostructure laser. An estimate of the duration of the superradiance pulse is given.

InAs self-organized quantum dots inserted in InGaAs quantum well have been grown on GaAs substrates by molecular beam epitaxy. The lateral size of the InAs islands has been found to be approximately 1.5 times larger as compared to the InAs/GaAs case, whereas the island heights and surface densities were close in both cases. The quantum dot emission wavelength can be controllably changed from 1.1 to 1.3 μm by varying the composition of the InGaAs quantum well matrix. Photoluminescence at 1.33 μm from vertical optical microcavities containing the InAs/InGaAs quantum dot array was demonstrated.

Spectral and spatial characteristics of the output of InGaAsP/InP separate-confinement double heterostructure laser are investigated. The measurements are performed in quasicontinuous and continuous pumping regimes at room temperature. These lasers are shown to be spatially single-mode over the entire working range of currents. The broadening of the longitudinal modes under quasicontinuous pumping is attributed to heating of the active region of the lasers. The pump pulse duration at which heating of the active region of the lasers can be neglected is estimated.

A thermodynamic approach has been developed for the case of the formation of surface segregation layers during MBE growth of III-V compounds and alloys. The more volatile group III element segregation on the growth surface of III-V alloys with several group III elements was found to be the main origin of their surface morphology degradation. The case of Sn segregation on GaAs and Al x Ga 1- x As surface during growth was also considered.

During the last decade the application of quantum-size-effect-heterostructures to solid state micro- and optoelectronics has attracted great attention, because it has made possible to improve drastically the parameters of most known devices and to invent new ones. Results are given of the investigation of the photoluminescence (PL), electroluminescence (EL), and galvanomagnetic properties of MBE-grown AIIIBV heterostructures with different sequences of ultrathin layers and short-period superlattices. The influence of introduction of such sequences on device structure characteristics is discussed. [Russian Text Ignored.]

This letter reports on the self-organized growth of nanoscale dot-like CdSe-based islands during molecular beam epitaxy of CdSe/ZnSe nanostructures with a CdSe thickness between 0.75 and 3.0 monolayers. An increase in the nominal CdSe thickness results in a higher density of islands (up to 2×1010 cm−2) and is accompanied by dramatic enhancement of the photoluminescence efficiency. The density of large relaxed islands appears to saturate at a value of (3–4)×109 cm−2. Room temperature (Zn, Mg)(S, Se)-based optically pumped lasers with an extremely low threshold (less than 4 kW/cm2), as well as (Be, Mg, Zn)Se-based injection laser diodes using a single (2.5–2.8) monolayer thick CdSe active region, both demonstrating significantly enhanced degradation stability, have been fabricated and studied.

We study the optical properties of structures composed of stacked InAs submonolayer insertions in an AlGaAs matrix grown on a GaAs(100) surface. The increased refractive index in the active region necessary for waveguiding is caused by the absorption peak due to excitons trapped by monolayer-height InAs islands. Despite a very low average InAs concentration, a thin AlGaAs buffer layer and an absorbing GaAs substrate photopumped lasing in the visible spectral range is already realized at low excitation density.

It is shown that GaN layers can be grown on (100)-and (111)-oriented porous single-crystal GaAs substrates by molecular-beam epitaxy with plasma activation of the nitrogen by an rf electron cyclotron resonance discharge. The resulting undoped epitaxial layers possessed ntype conductivity with a carrier concentration ∼1018. Data obtained by scanning electron microscopy and cathodoluminescence indicate that at thicknesses ∼2000 A, continuous layers of the cubic GaN modification are obtained regardless of the substrate orientation.

We observed a self-sustained current oscillation in an InGaAs/InAlAs superlattice at room temperature. The oscillation gave rise to microwave generation at a fundamental frequency around 2 GHz and higher harmonics. The power at the first harmonic was 0.1 mW, corresponding to an efficiency (i.e. ratio of microwave power to dc power) of 3.5%. We attribute the current oscillation to travelling dipole domains.

Characteristics of low-threshold ZnSe-based room-temperature green semiconductor alsers are studied in detail as dependent on transverse size (h ) of an active region. It is shown that the efficiency increases with increasing h , then passes through a maximum, and gradually falls down when h exceeds the cavity length L. The effect can be explained by taking into account the excitation of different transversal modes.© (2007) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Time‐resolved magneto‐photoluminescence spectroscopy is applied to elucidate dynamics of excitons in GaAs/AlGaAs/ZnSe/ZnCdMnSe heterovalent double quantum wells (QW). An essential slowdown of the recombination rate was observed, resulting from exciton localization due to the compositional disordering at the AlGaAs/ZnSe heterovalent interface. It was found that both exciton lifetime and spin lifetime can be controlled by varying the detuning of the single‐QW electron levels.

We report millimeter wave generation by a self-sustained current oscillation in a doped InGaAs/InAlAS wide miniband superlattice. The superlattice (miniband width 160 meV) showed, at room temperature, a current voltage characteristic with negative differential conductance. Coupled to a high-frequency circuit, the superlattice generated millimeter waves, at a frequency (55 GHz) which was tunable by half a percent by changing the bias voltage. The power (0.3 mW) corresponded to an efficiency (i.e., ratio of microwave power to dc power input) of 0.3%. We attribute the microwave generation to a current oscillation caused by traveling dipole domains.

We report the successful application of alternatively strained short-period superlattices for the waveguide region of optically pumped and injection room-temperature ZnSe-based lasers operating within the 470–523 nm spectral range. The design of optically pumped ZnMgSSe/ZnSSe/ZnCdSe lasers provides extremely low threshold power densities due to the enhanced electronic and optical confinement. Room-temperature BeMgZnSe/ZnCdSe injection lasers with threshold current density of about 750 A/cm2 and characteristic temperature as high as 366 K are demonstrated. The peculiarities of carrier transport across the short-period superlattices are explained by a thermally activated mechanism.

Spontaneous emission has been observed for the first time as a result of interband transitions of holes and electrons between size-quantization levels in vertically coupled quantum dots and also as a result of transitions from quantum-well states to a quantum-dot level. The spectral range of the emission was in the far-infrared (λ≅10–20 μm). The long-wavelength emission was only recorded simultaneously with short-wavelength interband emission (λ≅0.94 μm) in InGaAs/AlGaAs quantum-dot laser structures at above-threshold currents.

InAs quantum dots in a InGaAs matrix grown on an InP substrate by molecular-beam epitaxy are employed as the active region of an injection laser. Lasing via quantum-dot states is observed in the temperature range 77–200 K. At the lowest threshold current density 11 A/cm2 the radiation wavelength is equal to 1.894 µm (77 K).

Structures having a set of planes with submonolayer InAs inclusions in an AlGaAs matrix were fabricated and studied. Lasing was observed as a result of optical excitation. It is shown that lasing takes place via the ground state of excitons localized at InAs islands and may be achieved without external optical confinement of the active region by wide-gap layers of lower refractive index. The low threshold excitation density shows that these structures may be used to develop low-threshold injection lasers in the visible range, exciton waveguides, and self-contained microcavities.

The electroluminescent properties of quantum-well diode structures on staggered type-II heterojunctions in the InAs/GaSb system, obtained by molecular-beam epitaxy on InAs substrates, are investigated. Electroluminescence is observed in the spectral range 3–4 μm at T=77 K. It is found that emission bands due to recombination transitions involving electrons from the size-quantization levels of both the self-matched quantum wells at the InAs/GaSb type-II heterojunction and of the square quantum wells in short-period superlattices.

It is shown that GaN films can be grown by molecular-beam epitaxy with plasma activation of the nitrogen by a magnetron rf discharge in a specially constructed coaxial source with capacitive coupling. A growth rate of ∼0.1 μm/h is obtained on GaAs and sapphire substrates, and ways are found for optimizing the design of the plasma source in order to increase the growth rate. The electrophysical and luminescence properties of undoped epitaxial films are investigated at temperatures ranging all the way to room temperature.

Self-organized nano-objects fabricated in different semiconductor systems are currently at the focus of scientific interest because of their unique electronic properties. Transmission electron microscopy and high-resolution electron microscopy have been used to study the InAs quantum dots grown by molecular-beam epitaxy (MBE) on GaAs and InP substrates. Optimal imaging conditions for visualization of quantum dots were established. Size, shape, and stability of the equilibrium island arrays were analyzed with respect to the growth conditions. Both decrease and increase of the As pressure compared to the optimal value were shown to destroy the regular arrangement of the islands. Energy benefit due to the strain relaxation in the InAs islands is likely to be the driving force for their formation.

We report on a semiconductor superlattice oscillator for generation of millimeter waves (frequency 65 GHz). The main element of the oscillator is a doped short-period GaAs/AlAs superlattice with negative differential conductance. The oscillator is due to current oscillations caused by charge density domains. The oscillator delivered, at an efficiency of 0.2% for the conversion of electrical power to radiation power, a power of 100 μW in a bandwidth of the order of 200 kHz.

By inserting stacked sheets of nominally 0.7 monolayer CdSe into a ZnSe matrix we create a region with strong resonant excitonic absorption. This leads to an enhancement of the refractive index on the low-energy side of the absorption peak. Efficient waveguiding can thus be achieved without increasing the average refractive index of the active layer with respect to the cladding. Processed high-resolution transmission electron microscopy images show that the CdSe insertions form Cd-rich two-dimensional (Cd, Zn)Se islands with lateral sizes of about 5 nm. The islands act as quantum dots with a three-dimensional confinement for excitons. Zero-phonon gain is observed in the spectral range of excitonic and biexcitonic waveguiding. At high excitation densities excitonic gain is suppressed due to the population of the quantum dots with biexcitons.

InAs self-organized quantum dots in In0.53Ga0.47As and In0.52Al0.48As matrices have been grown on InP substrates by molecular beam epitaxy. The dot size in InGaAs has been found to be 3–4 times larger, but the areal density about an order of magnitude smaller than that in InAlAs. Low-temperature photoluminescence (PL) of the InAs/InGaAs quantum dots is characterized by a narrow (35 meV) PL line as compared to that of InAs/InAlAs quantum dots (170 meV). Quantum dot formation increases the carrier localization energy as compared to quantum well structures with the same InAs thickness in a similar manner for both InAs/InGaAs and InAs/InAlAs structures. The effect of the barrier band gap on the optical transition energy is qualitatively the same for quantum well and quantum dot structures. The results demonstrate a possibility of controlling the quantum dot emission wavelength by varying the matrix composition.

A p-i-n resonant tunnel diode is designed and investigated using photoluminescence (PL) spectroscopy. The device is based on an Al0.4Ga0.6As/GaAs graded-index waveguide heterostructure enhanced by aperiodic-superlattice injectors for simultaneous resonant injection of electrons and heavy holes. The bias-dependent study of photocurrent, electroluminescence (EL) and PL show strong resonance behavior in the optical intensity confirming the field-dependent resonant injection of the excited states in the emission layers. Pronounced voltage-current bistability due to injection efficiency leads to multiple-wavelength EL and lasing action.

Cyclotron resonance is measured in solitary type-II InAs-AlGaSb quantum wells grown by molecular-beam epitaxy under various growth conditions. Quantum oscillations observed in the cyclotron resonance spectra in InAs-GaSb samples are attributed to scattering by a short-range potential due to roughness of the heterointerface. A new method based on measurement of the cyclotron resonance spectra is proposed for assessing the quality of the heterointerface.

The luminescence properties of a GaN/Al0.1Ga0.9N double heterostructure grown by vapor-phase deposition from organometallic compounds are studied. When luminescence is observed from the end, the radiation intensity shows a sharply defined threshold dependence on the pump density. The threshold excitation density at T=77 K was ∼40 kW/cm2 and the wavelength of the stimulated emission was λ=357 nm. The long-wavelength shift of the emission line at high pump densities may be attributed to renormalization of the band gap caused by many-particle interactions in the electron-hole plasma.

We report on a millimeter wave oscillator based on a quasiplanar superlattice electronic device (SLED). The SLED, a lateral structured GaAs/AlAs superlattice, showing, at room temperature, a negative differential conductance, was provided with two terminals lying in one plane and mounted in a waveguide structure. The oscillator delivered radiation, in a relative bandwidth of 10−5, that was tunable by about 10% around 70 GHz and had a power of 100 μW; depending on the voltage across the superlattice, additional oscillation lines (up to 180 GHz) appeared. We associate the generation of radiation with a current oscillation caused by traveling dipole domains in the superlattice.

Contactless electroreflectance, at both 300 and 20 K, has been used to investigate a vertically coupled quantum dot (QD)-based InAs/GaAs laser structure. Signals have been observed from all the relevant portions of the sample including the QDs and wetting layer. The energies of the QD transitions provide evidence for both lateral as well as vertical coupling.

The photoluminescent properties of quantum dots formed in the deposition of an InSb thin film (1–3 monolayers) on GaAs(100) and GaSb(100) surface are investigated. The results indicate the importance of As-Sb substitution reactions in the formation of quantum dots on a GaAs surface.

It is shown that in order to achieve lasing in structures with CdSe submonolayers inserted in a ZnSe matrix, no additional optical confinement of the active region using thick wide-gap layers is required. The high oscillator strength of the excitons trapped at CdSe islands modulates the permittivity and thus produces a natural exciton-induced waveguiding effect.

Annealing at higher temperature (700 °C) of structures with two‐dimensional and three‐dimensional arrays in InAs–GaAs quantum dots (QDs) results in an increase in the size and in a corresponding decrease in the indium composition of the QDs. The change in the In composition is monitored by the contrast pattern in the plan‐view transmission electron microscopy (TEM) images viewed under the strong beam imaging conditions. Increase in the size of the QDs is manifested by the plan‐view TEM images taken under [001] zone axis illumination as well as by the cross‐section TEM images. We show that the dots maintain their geometrical shape upon annealing. Luminescence spectra demonstrate a shift of the QD luminescence peak toward higher energies with an increase in the annealing time (10–60 min) in agreement with the decrease in indium composition revealed in TEM studies. The corresponding decrease in the QD localization energy results in an effective evaporation of carriers from QDs at room temperature, and the in...

We demonstrate direct growth of electronically coupled zero‐dimensional structures forming a super‐quantum dot using metal‐organic chemical vapor deposition. After the first sheet with InGaAs pyramids is formed on GaAs surface, alternate short‐period GaAs‐InGaAs deposition leads to spontaneous formation of layered structures driven by the energetics of Stranski–Krastanow growth. As a result columnlike InGaAs structures each having a characteristic lateral size of ∼23 nm at the top and composed of many closely packed InGaAs parts are formed. The full width at half maximum of superdot luminescence of 28 meV at 8 K indicates good average uniformity of the superdot ensemble. Absorption is found to be resonant with luminescence.

In photoluminescence spectra of nanometer‐scale pyramidal‐shaped InAs/GaAs quantum dots allowed optical transitions involving excited hole states are revealed in addition to the ground state transition. Detailed theoretical calculations of the electronic structure, including strain, piezoelectric and excitonic effects, agree with the experimental data and lead to unambiguous assignment of the transitions.

We report on optical studies of relaxation processes in self‐organized InAs/GaAs quantum dots (QDs). Near resonant photoluminescence excitation spectra reveal a series of sharp lines. Their energy with respect to the detection energy does not depend on QD size and their energy separations are close to the InAs LO phonon energy of 32.1 meV estimated for strained pyramidal InAs QDs. The shape of the PLE spectra is explained by multiphonon relaxation processes involving LO phonons of the QD as well as of the wetting layer, an interface mode, and low frequency acoustical phonons.

Initial stage of InAs pseudomorphic layer transformation (1–3 ML) on GaAs (100) singular surface may result for sequential submonolayer molecular beam epitaxy in formation of a pseudoperiodic array of InAs ‘‘wires’’ along the [001] direction. Complex parquet structures having similar anisotropy are formed on misoriented surface (3° towards [0–11] direction). Increase in growth interruption time after each growth cycle for 2 ML InAs deposited on singular surface results in decomposition of the wires into dots arranged in a 2D square lattice. Intentional substrate misorientation stabilizes the initial ordering effect along [001] and does not change the direction of anisotropy.

Mie resonances due to scattering/absorption of light in InN containing clusters of metallic In may have been erroneously interpreted as the infrared band gap absorption in tens of papers. Here we show by direct thermally detected optical absorption measurements that the true band gap of InN is markedly wider than currently accepted 0.7 eV. Micro-cathodoluminescence studies complemented by imaging of metallic In have shown that bright infrared emission at 0.7-0.8 eV arises from In aggregates, and is likely associated with surface states at the metal/InN interfaces., 4 pages, 5 figures, submitted to PRL

Microphotoluminescence studies reveal strong and narrow lines of similar to1-meV minimal width in GaN/AlxGa1-xN quantum well (QW) structures having inversion domains (IDs). These narrow lines coexi ...