Showing papers by "Nikolai N. Ledentsov published in 1999"
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01 Jan 1999
TL;DR: In this paper, the growth and structural characterisation of self-organized Quantum Dots are discussed. But they do not consider the model of ideal and real quantum Dots.
Abstract: Fabrication Techniques for Quantum Dots. Self-Organization Concepts on Crystal Surfaces. Growth and Structural Characterization of Self-Organized Quantum Dots. Modeling of Ideal and Real Quantum Dots. Electronic and Optical Properties. Electrical Properties. Photonic Devices. References. Index.
2,356 citations
TL;DR: In this article, the lateral size of 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.
Abstract: 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.
359 citations
TL;DR: In this article, a diode laser based on self-organized quantum dots (QD's) on a GaAs substrate is demonstrated, where multiple stacking of InAs QD planes covered by thin InGaAs layers allows 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.
Abstract: 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.
115 citations
TL;DR: Gain characteristics of injection lasers based on self-organized quantum dots (QDs) were studied experimentally for two systems: InGaAs QDs in an AlGaAs matrix on a GaAs substrate as discussed by the authors.
Abstract: Gain characteristics of injection lasers based on self-organized quantum dots (QDs) were studied experimentally for two systems: InGaAs QDs in an AlGaAs matrix on a GaAs substrate and InAs QDs in an InGaAs matrix on an InP substrate. A ground-to-excited state transition was observed with increasing threshold gain. An empirical equation is proposed to fit the current density dependence of the QD gain. This fitting equation is shown to be valid for both the ground and excited state lasing in the systems under study in the 77-300 K temperature range. The effect of QD surface density on gain characteristics is calculated analytically.
80 citations
TL;DR: In this paper, an array of strained InAs nanoislands formed on a GaAs surface is overgrown by a thin (1-10 nm) layer of an indium-containing solid solution, stimulated decomposition of the solid solution is observed.
Abstract: When an array of strained InAs nanoislands formed on a GaAs surface is overgrown by a thin (1–10 nm) layer of an indium-containing solid solution, stimulated decomposition of the solid solution is observed. This process causes the formation of zones of elevated indium concentration in the vicinity of the nanoislands. The volume of newly formed InAs quantum dots increases as a result of this phenomenon, producing a substantial long-wavelength shift of the photoluminescence line. This effect is enhanced by lowering the substrate temperature, and it depends weakly on the average width of the band gap of the solid solution. The indicated approach has been used successfully in achieving room-temperature emission at a wavelength of 1.3 µm.
45 citations
TL;DR: In this article, a quantum dot laser based on arrays of self-organized quantum dots modified all the basic commandments of the heterostructure laser and provided new ways to control optical properties of the media.
Abstract: Despite its early age, laser based on arrays of self-organized quantum dots modified all the basic commandments of the heterostructure laser. Excitonic gain mechanism and discrete energy spectrum in a quantum dot provide principally new ways to control optical properties of the media. Extension of the spectral range using the same substrate will probably soon lead to the appearance of quantum dot lasers on the market.
24 citations
TL;DR: In this article, a method was proposed to increase the emission wavelength from structures grown on GaAs substrates by inserting a strained InAs quantum dot array into an external InGaAs quantum well.
Abstract: A method is proposed to increase the emission wavelength from structures grown on GaAs substrates by inserting a strained InAs quantum dot array into an external InGaAs quantum well. The dependence of the luminescence peak position on the active region design was investigated for structures grown by this method. Room-temperature photo-and electroluminescence spectra in the 1.3-µm wavelength range are compared.
20 citations
TL;DR: In this article, the feasibility of lasing at a wavelength close to 1.3 µm is demonstrated in InAs quantum-dot structures placed in an external InGaAs/GaAs quantum well.
Abstract: The feasibility of lasing at a wavelength close to 1.3 µm is demonstrated in InAs quantum-dot structures placed in an external InGaAs/GaAs quantum well. It is shown that the required wavelength can be attained with the proper choice of thickness of the InAs layer deposited to form an array of three-dimensional islands and with a proper choice of mole fraction of InAs in the InGaAs quantum well. Since the gain attained in the ground state is insufficient, lasing is implemented through excited states in the temperature interval from 85 K to 300 K in a structure based on a single layer of quantum dots. The maximum attainable gain in the laser structure can be raised by using three rows of quantum dots, and this configuration, in turn, leads to low-threshold (70 A/cm2) lasing through the ground state at a wavelength of 1.26 µm at room temperature.
15 citations
TL;DR: In this article, an array of (In,Al)As QDs demonstrating considerably higher density than Al-free QDs as nucleation centers for the injection laser formation was used.
14 citations
11 citations
TL;DR: In this paper, the current dependence of the optical gain in laser-based self-organized InGaAs quantum dots in a AlGaAs/GaAs matrix is investigated experimentally.
Abstract: 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.
TL;DR: In this paper, conditions for the injection of arsenic into gallium nitride layers grown by metal-organic vapor phase epitaxy were investigated and it was shown that the deposition of GaAs on a GaN surface relieves stresses in the GaN layer.
Abstract: Conditions are investigated for the injection of arsenic into gallium nitride layers grown by metal-organic vapor-phase epitaxy. It is shown that the deposition of GaAs on a GaN surface relieves stresses in the GaN layer. The high-temperature overgrowth of a thin GaAs layer by a GaN layer causes As atoms to diffuse into the GaN, produces a thick, homogeneously doped GaN:As region, and creates a bright band in the photoluminescence spectrum with a maximum at ∼2.5 eV.
TL;DR: In this paper, the optical properties of structures containing InGaAs quantum dots in GaAs and AlGaAs matrices grown by molecular-beam epitaxy are investigated, and it is shown that increasing the In content in the quantum dots has the effect of raising the energy of carrier localization and increasing the energy distance between the ground state and the excited states of quantum dots.
Abstract: The optical properties of structures containing InGaAs quantum dots in GaAs and AlGaAs matrices grown by molecular-beam epitaxy are investigated. It is shown that increasing the In content in the quantum dots has the effect of raising the energy of carrier localization and increasing the energy distance between the ground state and the excited states of carriers in the quantum dots. An investigation of the influence of postgrowth annealing on the optical properties of the structures shows that the formation of vertically coupled quantum dots and the use of a wide-gap AlGaAs matrix enhances the thermal stability of the structures. Moreover, high-temperature (830 °C) thermal annealing can improve the quality of the AlGaAs layers in structures with vertically coupled InGaAs quantum dots in an AlGaAs matrix. The results demonstrate the feasibility of using postgrowth annealing to improve the characteristics of quantum dot lasers.
TL;DR: In this article, the mechanism for heteroepitaxial growth in the InAs/Si system was studied by reflection highenergy electron diffraction, scanning tunnelling microscopy, and photoluminescence.
Abstract: The mechanism for heteroepitaxial growth in the InAs/Si system is studied by reflection highenergy electron diffraction, scanning tunnelling microscopy, and photoluminescence. For certain growth conditions, InAs nanostructures are found to develop on the Si surface immediately during the growth process in the course of molecular beam epitaxy. The range of substrate temperatures that lead to formation of nanosized islands is determined. InAs quantum dots grown on a buffer Si layer with a silicon layer of thickness 50 nm grown on the top produced photoluminescence lines at a wavelength of 1.3 µm at 77K and 1.6 µm at 300 K.
TL;DR: In this paper, the analytical form of the dependence of the gain on pump current density for laser diodes with an active region based on self-organized quantum dots is derived in a simple theoretical model.
Abstract: The analytical form of the dependence of the gain on pump current density for lasers with an active region based on self-organized quantum dots is derived in a simple theoretical model. The proposed model is shown to faithfully describe experimental data obtained for laser diodes based on InGaAs quantum dots in an AlGaAs/GaAs matrix, as well as InAs quantum dots in an InGaAs/InP matrix. The previously observed gain saturation and switching of the lasing from the ground state to an excited state of the quantum dots are studied. The influence of the density of quantum-dot arrays on the threshold characteristics of lasers based on them is examined on the basis of this model.
TL;DR: In this paper, the photoluminescence of self-organized InAs quantum dots (QDs) grown by conventional solid source molecular beam epitaxy (MBE) on a GaAs substrate was studied as a function of the deposition temperature.
TL;DR: The ground state of composite vertically coupled InAlAs/InGaAs quantum dots in an AlGaAs matrix with a room temperature output power of 3.3W at both mirrors was achieved in this article.
Abstract: Continuous-wave lasing has been achieved via the ground state of composite vertically coupled InAlAs/InGaAs quantum dots in an AlGaAs matrix with a room temperature output power of 3.3W at both mirrors.
TL;DR: In this article, it was shown that at high excitation densities one of the modes in the luminescence spectrum, which is modulated by modes of the Fabry-Perot cavity formed by the GaN/air and GaN-sapphire-substrate interfaces, is sharply amplified and begins to dominate the spectrum.
Abstract: Lasing is discovered in the direction perpendicular to the surface in quantum-size InGaN/GaN multilayer heterostructures grown by vapor-phase epitaxy. At high excitation densities one of the modes in the luminescence spectrum, which is modulated by modes of the Fabry-Perot cavity formed by the GaN/air and GaN/sapphire-substrate interfaces, is sharply amplified and begins to dominate the spectrum. The dependence of the luminescence intensity on pump density has a clearly expressed threshold character. The threshold excitation density in the vertical direction is 5–6 times greater than the stimulated-emission threshold for observation from an end surface of the structure. The gain coefficient in the active region at the threshold for surface-emitting lasing is estimated as 2×105 cm−1. The interaction between the cavity modes and the gain spectrum is detected in the form of displacement (by up to 2.6 nm) of modes on the short-wavelength edge of the luminescence spectrum toward higher photon nergies. The characteristic temperature (T0) measured in the range from 16 to 120 K is 480 K. At higher temperatures T0 K.
TL;DR: In this article, the effect of vertical alignment in the quantum dot array formed by successive deposition of several rows of InAlAs and InGaAs quantum dots separated by thin AIGaAs spacer layers was studied.
Abstract: In the present work we study the effect of vertical alignment in the quantum dot array formed by successive deposition of several rows of InAlAs and InGaAs quantum dots separated by thin AIGaAs spacer layers. Transmission electron microscopy and photoluminescence studies revealed that the InAlAs QDs characterized by high areal density force InGaAs to be transformed into the denser array as compared to the case of spontaneous transformation. Using denser array of composite quantum dots in the active region of a diode laser leads to the increase in modal gain, decrease in internal loss, and decrease in the threshold current density for short cavity diodes. Room temperature continuous wave output power as high as 3.3 W at 0.87 µm is achieved.
TL;DR: In this paper, 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.
Abstract: 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.
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26 Jul 1999
TL;DR: A quantum dot (QD) represents a semiconductor crystal with a size of several nanometers which demonstrates the basic properties of the atom, allowing new types of solid state devices.
Abstract: A quantum dot (QD), represents a semiconductor crystal with a size of several nanometers which demonstrates the basic properties of the atom, allowing new types of solid state devices. The possibility of achieving improved and temperature insensitive parameters of a semiconductor laser using QDs was proposed by Arakawa and Sakaki (1982). Later Asada et al. (1986) pointed to a possibility of using ultrahigh material gain in QDs. More than a decade passed until the first QD lasers were fabricated in 1993 and were proven to demonstrate some of the predicted properties. Recently significant interest arose for using QDs as active medium for VCSELs. In the approach lasers with ultralow total currents are fabricated, and, even more exciting, lasers based on a single QD can be potentially realized, as the spreading of nonequilibrium carriers important for small apertures is suppressed.
12 Nov 1999
TL;DR: In this article, a GaAs/AlAs superlattice detector was used for the detection of THz radiation, generated by a free-electron laser and a mode-locked p-Ge laser.
Abstract: We report on a GaAs/AlAs superlattice detector as a novel direct detector and autocorrelator for THz radiation. It is based on a doped wide-miniband GaAs/AlAs superlattice, with submonolayer AlAs barrier layers; the superlattice is operated at room temperature. THz radiation, generated by a free-electron laser and a mode locked p-Ge laser, was coupled into the superlattice via a corner cube antenna system. THz-irradiation of the biased superlattice resulted in a current reduction, which was monitored. The direct detector showed a fast response (20 ps, limited by the electronic circuit) and was robust against intense radiation pulses (peak power 10 kW). The responsivity was 100 times higher than the responsivity of detectors of comparable risetime and comparable robustness. Intense THz radiation caused a complete suppression of the current through the superlattice. This is the basis of the superlattice autocorrelator. The superlattice autocorrelator could resolve picosecond radiation pulses.
TL;DR: In this paper, the influence of growth conditions during molecular-beam epitaxy and of the degree of lattice mismatch between the epilayer and the substrate on the formation of InGaAs islands on a Si(100) surface is studied.
Abstract: The influence of the growth conditions during molecular-beam epitaxy and of the degree of lattice mismatch between the epilayer and the substrate on the formation of InGaAs islands on a Si(100) surface is studied. An increase in lattice mismatch (the InAs mole fraction) leads to an increase in the critical thickness corresponding to the onset of island growth, in contrast to the formation of InGaAs islands on GaAs(100). An increase in the deposition temperature also increases the critical thickness, whereas an increase in the arsenic pressure has the opposite effect. Structures containing an array of InGaAs islands in a Si matrix display a luminescence line in the range 1.2–1.3 µm, depending on the mole fraction of InAs.
06 Aug 1999
TL;DR: Quantum dot (QD) heterostructures as mentioned in this paper are nanoscale coherent insertions of narrow gap material in a single-crystalline matrix, which provide unique opportunities to modify and extend all the basic principles of heterostructure lasers and move further their applications.
Abstract: Quantum Dot (QD) heterostructures are nanoscale coherent insertions of narrow gap material in a single-crystalline matrix. These tiny structures provide unique opportunities to modify and extend all the basic principles of heterostructure lasers and move further their applications. Despite of its early age, QD lasers already demonstrate the capability to compete in some applications with more traditional heterostructure lasers based on quantum wells (QWs).
TL;DR: In this paper, the dependences of the reflection and photoluminescence spectra on the structural characteristics of the active region and optical cavities have been investigated, and the proposed heterostructures are potentially suitable for optoelectronic devices at wavelengths near 1.3 µm.
Abstract: Semiconductor heterostructures with vertical optical cavities with active regions, based on arrays of InAs quantum dots inserted in an external InGaAs quantum well, have been obtained by molecular-beam epitaxy on GaAs substrates. The dependences of the reflection and photoluminescence spectra on the structural characteristics of the active region and optical cavities have been investigated. The proposed heterostructures are potentially suitable for optoelectronic devices at wavelengths near 1.3 µm.
TL;DR: In this paper, the optical properties of structures with InAs islands and narrow GaAs quantum wells in an AlGaAs host have been investigated and the effect of an exciton waveguide and the onset of lasing due to optical pumping in the red spectral range are demonstrated in structures without external optical confinement by layers with a lower refractive index.
Abstract: The optical properties of structures with InAs islands and narrow GaAs quantum wells in an AlGaAs host have been investigated. The InAs islands were formed by depositing a layer of InAs with an effective thickness less than one monolayer. The effect of an exciton waveguide and the onset of lasing due to optical pumping in the red spectral range are demonstrated in structures without external optical confinement by layers with a lower refractive index.
26 Jul 1999
TL;DR: In this article, the authors studied the room temperature characteristics of the broad area (200 /spl mu/m) diode lasers based on triple-stacked InAs QDs covered with 5.5 nm In/sub 0.13/Ga/ sub 0.87/As QW.
Abstract: Self-assembled In(Ga)As quantum dots (QDs) formed in a GaAs matrix usually emit in the 1-1.2 /spl mu/m wavelength range. It is strongly desired to extend the emission range of QD structures grown on GaAs substrates up to 1.3 /spl mu/m to fit the transparency window of optical fibers. In the present work we study the room temperature characteristics of the broad area (200 /spl mu/m) diode lasers based on triple-stacked InAs QDs covered with 5.5 nm In/sub 0.13/Ga/sub 0.87/As QW. QD planes were separated by 30 nm GaAs spacers.