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A. Kosogov

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Papers by A. Kosogov

Self-organization processes of InGaAs/GaAs quantum dots grown by metalorganic chemical vapor deposition

Applied Physics Letters

In 0.5 Ga 0.5 As/GaAs ͑001͒ quantum dots ͑QDs͒ were grown by metalorganic chemical vapor depositi... more In 0.5 Ga 0.5 As/GaAs ͑001͒ quantum dots ͑QDs͒ were grown by metalorganic chemical vapor deposition ͑MOCVD͒ on exactly ͑001͒ oriented substrates using the Stranski-Krastanow growth mode. The dot density and their relative geometrical arrangement are found to be strongly dependent on the substrate temperature. The dots have identical square shaped bases oriented along ͗100͘. For high densities a preferential relative alignment of the dots along the ͗110͘ directions is found. These dots tend to be arranged in a chainlike pattern with decreasing dot size towards the ends of the chains. From these observations the dot formation process for In 0.5 Ga 0.5 As quantum dots is suggested to be driven by energetics whereas the relative orientation is governed by kinetic effects. © 1996 American Institute of Physics.͓S0003-6951͑96͒00923-0͔

Formation of Stacked Self-Assembled InAs Quantum Dots in GaAs Matrix for Laser Applications

MRS Proceedings, 1995

Growth, characterizations, theory and lasing of vertically stacked quantum dots

Proceedings of 8th International Conference on Indium Phosphide and Related Materials, 1996

We investigate multiple sheets of self-organized InAs quantum dots (QD's) with thin GaAs spacer l... more We investigate multiple sheets of self-organized InAs quantum dots (QD's) with thin GaAs spacer layers. The QD's spontaneously form on top of each other and couple electronically. In comparison to single sheets of QD's (SQD's), the coupling leads to lower energy levels and an expansion of the wavefunction. Thus carrier localization and gain increase. Threedimensional strain distribution and electronic structure are theoretically modeled. Laser operation of vertically coupled quantum dots (VECOD's) improves largely as compared to SQD lasers and room temperature operation with a threshold of 680Akm2 is obtained for a triple stack.

Static and dynamic properties of (InGa)As/GaAs quantum dot lasers

LEOS '95. IEEE Lasers and Electro-Optics Society 1995 Annual Meeting. 8th Annual Meeting. Conference Proceedings, 1995

Threshold current, polarization and carrier dynamics in (InGa)As/GaAs quantum dot (QD) structures... more

Direct formation of vertically coupled quantum dots in Stranski-Krastanow growth

Physical review. B, Condensed matter, Jan 15, 1996

Alternate short-period GaAs-InAs deposition following InAs pyramid formation on a GaAs (100) surf... more

$Research paper thumbnail of Structural characterization of self-assembled quantum dot structures by X-ray diffraction techniques$

Structural characterization of self-assembled quantum dot structures by X-ray diffraction techniques

Thin Solid Films, 1997

We have investigated, by means of X-ray diffraction reciprocal space mapping and X-ray reflectivi... more We have investigated, by means of X-ray diffraction reciprocal space mapping and X-ray reflectivity, multilayers of self-organized InGaAs quantum dots grown on GaAs by MBE. An anisotropy of the average inter-dot spacings in the [100]and [110]directions was found, consistent with an ordering of the dots in a two-dimensional square lattice with main axes along the -directions and a lattice parameter

$Research paper thumbnail of Lateral and vertical ordering in multilayered self-organized InGaAs quantum dots studied by high resolution x-ray diffraction$

Lateral and vertical ordering in multilayered self-organized InGaAs quantum dots studied by high resolution x-ray diffraction

Applied Physics Letters, 1997

We have studied multiple layers of self-organized InGaAs-islands grown on GaAs by x-ray diffracti... more We have studied multiple layers of self-organized InGaAs-islands grown on GaAs by x-ray diffraction reciprocal space mapping. We found an anisotropy of the dot spacing in [100] and [110] direction consistent with an ordering of the dots in a two-dimensional square lattice with main axes along the [100] direction and a lattice parameter of 55 nm. The nearly perfect vertical

Structural and optical properties of InAs-GaAs quantum dots subjected to high temperature annealing

Applied Physics Letters, 1996

Annealing at higher temperature (700 °C) of structures with two-dimensional and three-dimensional... more 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

Growth of self-assembled homogeneous SiGe-dots on Si(100)

Thin Solid Films, 1997

Semiconductor quantum dots for application in diode lasers

Thin Solid Films, 1998

. Recent progress in the epitaxy molecular beam epitaxy and metal-organic chemical vapor depositi... more . Recent progress in the epitaxy molecular beam epitaxy and metal-organic chemical vapor deposition of strained heterostructures and the use of the Stranski-Krastanow growth mode allows to create spontaneously ordered, defect-free and dense arrays of nano-size islands. Such islands act as electronic quantum dots. In superlattices the islands are ordered in vertical stacks. Using such self-ordered InGaAsrAlGaAs quantum dots we have fabricated diode lasers for which some properties are superior to those of current lasers based on quantum wells. In particular, we have demonstrated low laser threshold current and high temperature stability of the threshold. q 1998 Elsevier Science S.A.

Ordered arrays of quantum dots: Formation, electronic spectra, relaxation phenomena, lasing

Solid-State Electronics, 1996

Optical properties of vertically coupled InGaAs quantum dots in a GaAs matrix

Semiconductors, 1997

ABSTRACT

Self organization phenomena of quantum dots grown by metalorganic chemical vapour deposition

Journal of Crystal Growth, 1997

We have systematically investigated the influence of MOCVD growth parameters on structural and op... more We have systematically investigated the influence of MOCVD growth parameters on structural and optical properties of InxGa]_xAs/GaAs quantum dots (QDs) formed in the Stranski-Krastanow growth mode. The influence of growth interruption time, V/III ratio, In/Ga flux ratio and growth temperature was examined by photoluminescence (PL), transmission electron microscopy (TEM) and atomic force microscopy (AFM). For samples with high dot densities (up to 8 × 10 I° cm -2) the dots surprisingly show a preferential alignment along the (110) orientations differing from predictions of strain relaxation equilibrium theory and results for MBE grown InAs/GaAs dots. The square base shape of the quantum dots is oriented along (100) in agreement with MBE results and theoretical predictions.

Low-threshold injection lasers based on vertically coupled quantum dots

Journal of Crystal Growth, 1997

We have fabricated and studied injection lasers based on vertically coupled quantum dots (VECODs)... more We have fabricated and studied injection lasers based on vertically coupled quantum dots (VECODs). VECODs are self-organized during successive deposition of several sheets of (In,Ga)As quantum dots separated by thin GaAs spacers. VECODs are introduced in the active region of a GaAs-A1GaAs GRIN SCH lasers. Increasing the number of periods (N) in the VECOD leads to a remarkable decrease in threshold current density ( ~ 100 A/cm 2 at 300 K for N = 10). Lasing proceeds via the ground state of the quantum dots (QD) up to room temperature. Placing the QD array into an external AIGaAs--GaAs quantum well allows us to extend the range of thermal stability of threshold current density (To = 350 K) up to room temperature. Using (In,Ga)As-(A1,Ga)As VECODs in combination with high temperature growth of emitter and waveguide layers results in further reduction of threshold current density (60-80 A/cm 2, 300 K) and increase in internal quantum efficiency (70%). Room temperature continuous wave operation (light output 160 mW per mirror) and lasing via the states of QDs up to I = (6-7) Ith have been demonstrated.

High-power continuous-wave operation of a InGaAs/AlGaAs quantum dot laser

Journal of Applied Physics, 1998

A 1 W continuous-wave laser operation via the ground state of vertically coupled InGaAs quantum d... more A 1 W continuous-wave laser operation via the ground state of vertically coupled InGaAs quantum dots ͑VCQDs͒ in an AlGaAs matrix is demonstrated. VCQDs are directly revealed in transmission electron microscopy images of the laser structure. Ninety-six percent internal quantum efficiency is realized. The laser gain maximum shifts significantly with drive current towards higher photon energies in agreement with the relatively broad size distribution of VCQDs. © 1998 American Institute of Physics. ͓S0021-8979͑98͒01210-9͔

$Research paper thumbnail of High Resolution X-Ray Diffraction and Reflectivity Studies of Vertical and Lateral Ordering in Multiple Self-Organized InGaAs Quantum Dots$

High Resolution X-Ray Diffraction and Reflectivity Studies of Vertical and Lateral Ordering in Multiple Self-Organized InGaAs Quantum Dots

Japanese Journal of Applied Physics, 1997

Self-assembled Ge dots: Growth, characterization, ordering, and applications

… B: Microelectronics and …, 1998

The Stranski-Krastanow growth mode, which leads to the self-assembled formation of dots, allows o... more The Stranski-Krastanow growth mode, which leads to the self-assembled formation of dots, allows one to exceed the critical thickness without introducing dislocations. We report the coverage limits for the dislocation-free dot regime in dependence of the Ge content, and also the composition dependent thickness of the two-dimensional wetting layer. To reduce the size inhomogeneity of the self-assembled dots, we investigated ordering effects in Si/Ge-dot multilayers. The experiments do not only reveal a strong vertical ordering of the dots, but also a lateral correlation and a significantly increased size homogeneity is observed. Results on first device structures, a npn-infrared detector and a silicon based tunneling structure, both with embedded layers of self-assembled Ge dots, are presented.

Self organized defect free InAs/GaAs and InAs/InGaAs/GaAs quantum dots with high lateral density grown by MOCVD

Applied Surface Science, 1998

We report on the growth of InAs/GaAs and InAs/InGaAs/GaAs quantum dots (QDs) by metalorganic chem... more We report on the growth of InAs/GaAs and InAs/InGaAs/GaAs quantum dots (QDs) by metalorganic chemical vapor deposition (MOCVD). High density, defect-free InAs/GaAs quantum dots can only be grown in a narrow growth parameter window. The optimum thickness range of ~ 1.65 monolayers (MLs) has to obeyed within _+ 10% in order to obtain defect-free high density (10 ~ cm 2) QDs. During the growth interruption after the InAs deposition, the AsH 3 flux also has to be switched off in order to avoid the formation of incoherent clusters. Under optimized conditions, high quality QD stacks with various separation layer thickness have been obtained. A reduction of the inhomogeneous broadening and an increase in efficiency of the room temperature luminescence is observed when the QDs are covered with a thin ternary In0s Ga07 As layer before the deposition of the GaAs cap layer.

Properties of strained (In, Ga, Al)As lasers with laterally modulated active region

Applied Physics Letters, 1997

Transmission electron microscopy studies of low indium composition In x Ga 1Ϫx As insertions ͑xϽ0... more Transmission electron microscopy studies of low indium composition In x Ga 1Ϫx As insertions ͑xϽ0.4͒ in a GaAs matrix deposited by molecular beam epitaxy or by metal-organic chemical vapor deposition reveal nanoscale quasiperiodic compositional and morphological modulations. The luminescence peak wavelength is found to be a strong function of deposition parameters and can be tuned from 1.1 to 1.3 m for the same x and average thickness of the deposit. Strained ͑In, Ga, Al͒As lasers with such a laterally modulated In x Ga 1Ϫx As active region demonstrate significant depolarization of the electroluminescence. For short cavity length, lasing occurs at energies corresponding to transitions between In x Ga 1Ϫx As conduction band and light holelike valence band states. Devices lase at low threshold current densities and demonstrate continuous wave operation up to 3 W at room temperature.

Formation of coherent superdots using metal-organic chemical vapor deposition

Applied Physics Letters, 1996

We demonstrate direct growth of electronically coupled zero-dimensional structures forming a supe... more 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 ϳ23 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. © 1996 American Institute of Physics. ͓S0003-6951͑96͒01434-9͔