Showing papers by "Nikolai N. Ledentsov published in 2000"
TL;DR: In this article, the authors used the concept of electronically-coupled quantum dots (QDs) and oxide-defined 10 μm apertures for surface-emitting QD lasers (300 K).
213 citations
TL;DR: In this article, a model of self-organized quantum dots overgrown with an InGa(Al)As alloy layer is investigated as a means to control the structural and electronic properties.
Abstract: Strain-driven decomposition of an alloy layer is investigated as a means to control the structural and electronic properties of self-organized quantum dots. Coherent InAs/GaAs islands overgrown with an InGa(Al)As alloy layer serve as a model system. Cross-section and plan-view transmission electron microscopy as well as photoluminescence (PL) studies consistently indicate an increase in height and width of the island with increasing indium content and/or thickness of the alloy layer. The increasing island size is attributed to the phase separation of the alloy layer driven by the surface strain introduced by the initial InAs islands. The decomposition is enhanced by the addition of aluminum to the alloy layer. The ground-state transition energy in such quantum dots is significantly (up to 200 meV) redshifted compared to the original InAs/GaAs quantum dots, allowing to reach the 1.3 \ensuremath{\mu}m spectral region maintaining the high PL efficiency and the low defect density typical for Stranski-Krastanow growth. The possibility of degradation less stacking of such quantum dot layers enables injection lasing on the ground-state transition with a differential efficiency of 57% and a continuous-wave output power of 2.7 W.
196 citations
TL;DR: In this paper, a self-organized growth of QD's allowed the fabrication of dense arrays of coherent islands, uniform in shape and size, and, simultaneously, free from undesirable defects.
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 basic principles of heterostructure lasers and advance their applications. Despite early predictions, fabrication of QD heterostructure (QDHS) lasers appeared to be a much more challenging task, as compared to quantum well (QW) devices. The breakthrough occurred when techniques for self-organized growth of QD's allowed the fabrication of dense arrays of coherent islands, uniform in shape and size, and, simultaneously, free from undesirable defects. Recently, the figure of merit of QDHS lasers surpasses some of the key characteristics of QW devices in some of the most important applications.
188 citations
TL;DR: In this article, the authors present results on metal-organic chemical vapor phase deposition (MOCVD) and molecular beam epitaxy (MBE) grown high power QD lasers (up to 4 W front facet cw) based on InGaAs QDs on GaAs substrate.
Abstract: Quantum dot (QD) lasers have decisive advantages compared to quantum well lasers. Zero-dimensional charge carrier localization and reduction of charge carrier diffusion result in reduced non-radiative surface recombination and thus possibly reduced facet overheating and larger catastrophic optical damage (COD) threshold, crucial for high power operation. The emission wavelengths of 1100 nm?1300 nm are easily realized using QDs on GaAs substrate, not available with traditional quantum wells of the same material system. We present results on metal-organic chemical vapor phase deposition (MOCVD) and molecular beam epitaxy (MBE) grown high power QD lasers (up to 4 W front facet cw) based on InGaAs QDs on GaAs substrate
40 citations
TL;DR: In this article, the authors showed that the main reason for the long-wavelength PL shift in InAs/InGaAs quantum dots is non-uniform distribution of In in InGaAs leading to the increase in effective volume of a quantum dot.
Abstract: We study 1.3 µm diode lasers based on self-organized InAs quantum dots grown by molecular beam epitaxy on GaAs substrates. Overgrowing the InAs quantum dot array with a thin InGaAs layer allows us to achieve 1.3 µm emission and keep a sufficiently high surface density of quantum dots. Using transmission electron microscopy we show that the main reason for the long-wavelength PL shift in InAs/InGaAs quantum dots is non-uniform distribution of In in InGaAs leading to the increase in effective volume of a quantum dot. Long-stripe lasers showed low-threshold current density ( 50%) and low internal loss (~1-2 cm-1). The maximum output power for wide-stripe lasers was as high as 2.7 W and for single-mode devices 110 mW. The lasing wavelength for VCSELs was 1.3 µm. The threshold current for the device with the 8 µm aperture was 1.8 mA. The output power of 220 µW at a drive current of 2.4 mA was observed under pulsed mode.
20 citations
TL;DR: In this article, the influence of in situ annealing of the InGaAs layer in p-n InGaA/GaAs structures grown by the metalloorganic chemical vapor deposition upon the formation of coherently strained three-dimensional islands was investigated.
Abstract: A report is presented on the investigation of the influence of in situ annealing of the InGaAs layer in p-n InGaAs/GaAs structures grown by the metalloorganic chemical vapor deposition upon the formation of coherently strained three-dimensional islands. The structures were studied by the methods of capacitance-voltage measurements, deep-level transient spectroscopy, transmission electron microscopy, and photoluminescence. It is established that three-dimensional islands with misfit dislocations are formed in the unannealed structure A, while quantum dots are formed in the annealed structure B. The deep-level defects were investigated. In structure A, defects of various types (EL2, EL3 (I3), I2, HL3, HS2, and H5) are present in the electron-accumulation layer. Concentrations of these traps are comparable to the shallow donor concentration, and the number of hole traps is higher than that of the electron traps. On the in situ annealing, the EL2 and EL3 defects, which are related to the formation of dislocations, disappear, and concentrations of the other defects decrease by an order of magnitude or more. For structure A, it is established that the population of the quantum states in the islands is controlled by the deep-level defects. In structure B, the effect of the Coulomb interaction of the charge carriers localized in the quantum dot with the ionized defects is observed.
20 citations
TL;DR: In this article, the effects of nonradiative damping of the exciton resonance in the quantum wire on the optical response of the microcavity structure have been analyzed.
Abstract: Exciton-light coupling in cylindrical microcavities containing quantum wires has been treated by means of classical electrodynamics within the nonlocal dielectric response model. A typical anticrossing behavior of quasi-one-dimensional exciton-polariton modes has been obtained, as well as the weak-coupling--strong-coupling threshold. Effects of the nonradiative damping of the exciton resonance in the quantum wire on the optical response of the microcavity structure have been analyzed.
16 citations
TL;DR: Spatially singlemode lasing in the wavelength range of 125-128 µm was accomplished in injection lasers on GaAs substrates as discussed by the authors.The peak output power was 110 mW at room temperature, and the differential quantum efficiency amounts to 37%
Abstract: Spatially single-mode lasing in the wavelength range of 125–128 µm was accomplished in injection lasers on GaAs substrates The peak output power is 110 mW at room temperature, and the differential quantum efficiency amounts to 37% The active region of the laser is formed by an array of self-organizing InAs quantum dots
13 citations
TL;DR: In this paper, the optical properties of vertically coupled quantum dots grown by the combined submonolayer molecular-beam epitaxy were investigated, and it was shown that the formation of the laterally coupled conglomerates of quantum dots are possible in upper rows for certain parameters of growth, with corresponding photoluminescence emission being in the wavelength range of 1.3 µm at room temperature.
Abstract: Optical properties of structures with vertically coupled quantum dots grown by the combined submonolayer molecular-beam epitaxy were investigated. It is shown that the formation of the laterally coupled conglomerates of quantum dots are possible in upper rows for certain parameters of growth, with the corresponding photoluminescence emission being in the wavelength range of 1.3–1.4 µm at room temperature.
12 citations
TL;DR: In this article, the content of indium in nanodomains, determined by the DALI method, is as high as x≈0.6 or more, substantially exceeding the average In concentration.
Abstract: MOCVD-grown heterostructures with one or several InxGa1−x
N layers in a GaN matrix have been studied by transmission electron microscopy. In heterostructures with thick InGaN layers, a noncoherent system of domains with lateral dimensions (∼50 nm) on the order of the layer thickness (∼40 nm) is formed. In the case of ultrathin InGaN inclusions, nanodomains coherent with the GaN matrix are formed. The content of indium in nanodomains, determined by the DALI method, is as high as x≈0.6 or more, substantially exceeding the average In concentration. The density of the nanodomains formed in the structures studied is n≈(2–5)×1011 cm−2. In the structures with ultrathin InGaN inclusions, two characteristic nanodomain sizes are observed (3–6 and 8–15 nm).
7 citations
TL;DR: In this paper, a method for growing stacked stacked InAs/InGaAs self-organized quantum dots on GaAs substrates is proposed, which allows fabrication of structures exhibiting intense and narrow-line photoluminescence in the 1.3 µm wavelength region.
Abstract: A method is proposed for growing stacked InAs/InGaAs self-organized quantum dots on GaAs substrates. The technique allows fabrication of structures exhibiting intense and narrow-line photoluminescence in the 1.3 µm wavelength region. The influence of growth conditions on structural and optical characteristics was studied. The proposed structures show promise in developing vertical-cavity surface-emitting devices.
14 Jul 2000
TL;DR: Theoretical study of threshold characteristics of a quantum dot (QD) laser in the presence of excited-state transitions is given in this paper, where the effect of microscopic parameters (degeneracy factor and overlap integral for a transition) on the gain is discussed.
Abstract: Theoretical study of threshold characteristics of a quantum dot (QD) laser in the presence of excited-state transitions is given. The effect of microscopic parameters (degeneracy factor and overlap integral for a transition) on the gain is discussed. An analytical equation for the gain spectrum is derived in an explicit form. Transformation of the gain spectrum with the injection current is analyzed. The threshold current density is calculated as a function of the total losses. The conditions for a smooth or step-like change in the lasing wavelength with the losses are formulated. Threshold characteristics of a laser based on self-assembled pyramidal InAs QDs in GaAs matrix are simulated. A small overlap integral for transitions in such QDs (and hence large spontaneous radiative lifetime) is shown to be a main possible reason for a low value of the maximum single-layer modal gain of the respective structure which is deficient to attain lasing at moderately short (several hundreds of micrometers) cavity lengths.
TL;DR: In this paper, high resolution transmission electron microscopy was used to study MBE-grown multilayer structures with InAs quantum dots embedded in a crystalline silicon matrix, and it was shown that the silicon matrix can accommodate only a limited volume of InAs in the form of coherent clusters about 3 nm in size.
Abstract: MBE-grown multilayer structures with InAs quantum dots embedded in a crystalline silicon matrix were studied by high resolution transmission electron microscopy. The properties of the grown structures depend critically on the substrate temperature, growth cycle sequence, and layer thicknesses. It is shown that the silicon matrix can "accommodate" only a limited volume of InAs in the form of coherent clusters about 3 nm in size. With an increasing amount of deposited InAs, large dislocated InAs clusters are formed during Si overgrowth, accumulating excess InAs. © 2000 MAIK "Nauka/Interperiodica".
01 Jan 2000
TL;DR: In this paper, the authors used metal-organic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE) for the use in vertical cavity surface emitting laser diodes.
Abstract: InGaAs quantum dots (QD's) on GaAs substrate have been fabricated using metal-organic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE) for the use in vertical cavity surface emitting laser diodes. Similar recombination spectra are obtained by employing the two different approaches of seeding and overgrowth with a quantum well. Despite the shift to larger wavelengths a large separation (=80 meV) between excited states is maintained. The introduction of such QD's into a vertical cavity leads to strong narrowing of the emission spectrum. Lasing from a 1300 nm InGaAs quantum dot VCSEL is reported.
TL;DR: In this article, the effect of InGaAlAs solid solution decomposition stimulated by a purposely deposited layer of InAs quantum dots is studied, which results in an increase in the effective quantum dot size and shift of the photoluminescence line to as far as 1.3 µm.
Abstract: Mechanisms of InGaAlAs solid solution decomposition stimulated by a purposely deposited layer of InAs quantum dots are studied. Decomposition of the solid solution results in an increase in the effective quantum dot size and the shift of the photoluminescence line to as far as 1.3 µm. When aluminum atoms are added to the solid solution, the effect of In atom “conservation” within the dots is observed, which also causes an increase in the effective dot size.
TL;DR: In this paper, the power conversion efficiency of laser diodes with an array of quantum dots in the active region is analyzed and a model is proposed which allows analytical determination of the optimal cavity length corresponding to the highest conversion efficiency for a given output power.
Abstract: The power conversion efficiency of laser diodes with an array of quantum dots in the active region is analyzed. A model is proposed which allows analytical determination of the optimal cavity length corresponding to the highest conversion efficiency for a given output power. A comparison is made with experimental data for high-power lasers based on submonolayer quantum dots emitting at 0.94 µm.
14 Jul 2000
TL;DR: In this article, the authors proposed a quantum dot (QD) heterostructures with dimensionality lower than two in semiconductor lasers, which can be used to extend the basic principles of heterostructure lasers and achieve high power operation, record low threshold current densities, strongly reduced chirp and extension of the wavelength range on GaAs substrates.
Abstract: Nanoscale coherent insertions of narrow gap material in a single-crystalline matrix, or Quantum Dot (QD) provide a possibility to extend the basic principles of heterostructure lasers. The idea to use heterostructures with dimensionality lower than two in semiconductor lasers appeared a quarter of a century ago, simultaneously with the proposal of a quantum well laser. However, fabrication of quantum wire- and, particularly, QD heterostructure (QDHS) lasers appeared to be much more difficult. The breakthrough occurred when techniques for self-organized growth of QDs allowed fabrication of dense arrays of uniform in shape and size coherent islands free from undesirable defects. Recently, some key parameters of QD lasers were significantly improved as compared to those for QW devices. High-power operation, record low threshold current densities, strongly reduced chirp and extension of the wavelength range on GaAs substrates up to 1.3 micrometer range were demonstrated. It also became clear that unique properties of QDs may give rise to a new generation of semiconductor lasers, such as far and middle infrared light emitters based on interlevel electron transitions in QDs or single quantum dot vertical-cavity surface-emitting lasers.
TL;DR: In this paper, the properties of InGaAsN/GaAs heterostructures with quantum wells on GaAs substrates were studied, and the long-wavelength emission in the quantum wells was obtained in the wavelength range up to 1.32 μm at room temperature.
Abstract: The properties of InGaAsN/GaAs heterostructures with quantum wells on GaAs substrates were studied. The GaAsN layers containing InGaAsN quantum wells with a high (exceeding 1%) nitrogen concentration were obtained. The long-wavelength emission in the InGaAsN quantum wells is obtained in the wavelength range up to 1.32 μm at room temperature. The effect of the InGaAsN quantum parameters on the optical properties of heterostructures is studied.
12 Jul 2000
TL;DR: In this article, a small insertion of the semiconductor material having a small band gap in a wide band-gap matrix or quantum dots (QDs) give unique opportunities to modify and extend basic principles of modem lasers, improve their parameters and advance application.
Abstract: Tiny insertions of the semiconductor material having a small band-gap in a wide band-gap matrix, or quantum dots (QDs) give unique opportunities to modify and extend basic principles of modem lasers, improve their parameters and advance application [1]