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We investigate the electronic properties of InAs/GaAs quantum dots using capacitance transient spectroscopy after charging by illumination. This method combines the advantages of optical spectroscopy of inter-band exciton transitions and electrical charge detection methods. The emission of holes is observed after monochromatic optical charging. It is shown that resonant absorption leads to size-selective charging of sub-ensembles of quantum dots.

By selective doping of the well and barrier regions of p-GaAs/AlGaAs structures we have realized the situation where the upper Hubbard band (A + centers) has been occupied by holes in equilibrium. Hall effect and conductivity measurements have shown that the binding energy of A + centers increases significantly (five times) with respect to the bulk case for well width of 15 nm; it is related to the comparability between the well width and the radius of the A + state. In the low temperature region the conductivity has the character of 2D Mott-type variable range hopping (VRH). Basing on the analysis of quadratic positive magnetoresistance and non-ohmic VRH we have obtained estimates of the localization length. The value of 11 nm obtained is by a factor of five larger than the Bohr radius of the single hole state. The results unambiguously evidence that the hopping transport in our system is over states of the upper Hubbard band.

We report the use of an InGaAs/InAlAs superlattice for detection of THz radiation pulses generated by a free-electron-laser (FELIX). The detector showed a response corresponding to a reduction of the direct current through the superlattice. The current reduction is attributed to the THz-field induced modulation of Bloch oscillations performed by miniband electrons. The detector response was measured in a frequency range between 4 and 12 THz and showed strong minima at the frequencies of infrared active transverse optic phonons.

Certain cases are studied in which quantum dots (QDs) show no collective properties. It is demonstrated that physically isolated QDs (IQDs) are typical of the single-layer metastable QD arrays grown by submonolayer migration enhanced epitaxy on vicinal substrates. Their formation is attributed to the isolation of separate InAs clusters on vicinal terraces due to the wetting layer ruptures on the edges of bunched multiatomic steps. The carrier exchange between such QDs is not observed. Coalesced QDs formed in upper layers are typical of multi-layer metastable arrays. The lateral carrier exchange between such QDs is inhibited up to 300 K due to the effective electron channelling from them to underlying layers. It is demonstrated that the appearance of such isolated conglomerates results in the anomalous temperature dependence of photoluminescence (PL) for the multi-layer array. A model is proposed, which explains the influence of IQDs on the 3D array PL.

GaAs/AlAs superlattices grown simultaneously on GaAs substrates with the (311)A and (311)B orientations have been studied by photoluminescence and high-resolution transmission electron microscopy with a Fourier analysis of images. A periodic interface corrugation is observed for (311)B superlattices. A comparison of the structure of (311)A and (311)B superlattices indicates that the corrugation occurs in both cases and its period along the \([01\overline 1 ]\)direction is equal to 3.2 nm. The corrugation is less pronounced in (311)B superlattices, wherein it exhibits an additional modulation (long-wavelength disorder) with the characteristic lateral size exceeding 10 nm. The vertical correlation of regions rich in GaAs and AlAs, which is well observed in (311)A superlattices, is weak in (311)B superlattices due to the occurrence of long-wavelength disorder. The optical properties of (311)B superlattices are similar to those of (100) ones and differ radically from those of (311)A superlattices. As distinct from (311)B, strong photoluminescence polarization anisotropy is observed for (311)A superlattices. It is shown that it is the interface corrugation rather than the crystallographic (311) surface orientation that determines the optical properties of (311)A corrugated superlattices with thin GaAs and AlAs layers.

Results for interband and intraband absorption and emission in quantum dot structures are presented The observed peaks correspond to interband electron transitions between ground and excited states of QDs. Near infrared (λ ≃ 1 μm) lasing was obtained at high intensities of excitation. Surface mid infrared (λ > 10 μm) photoluminescence connected with the intraband electron transitions between the states of wetting layer and the ground states in QDs was also studied.

Full text: Semiconductor quantum dot lasers are attractive for multipletechnological applications in biophotonics. Simultaneous two-state lasing ofground state (GS) and excited state (ES) electrons and holes in QD lasers ispossible under a certain parameter range. It has already been investigated in steady-stateoperations and in dynamical regimes and is currently a subject of the intesiveresearch. It has been shown that the relaxation frequency in the two-state lasingregime is not a function of the total intensity [1], as could be traditionallyexpected.In this work we study damping relaxation oscillations in QD lasersimultaneously operating at two transitions, and find that under variouspumping conditions, the frequency of oscillations may decrease, increase orstay without change in time as shown in Fig1.The studied QD laser structure wasgrown on a GaAs substrate by molecular-beam epitaxy. The active region includedfive layers of self-assembled InAs QDs separated with a GaAs spacer from a5.3nm thick covering layer of InGaAs and processed into 4mm-wide mesa stripe devices. The 2.5mm long lasers withhigh-and antireflection coatings on the rear and front facets lasesimultaneously at the GS (around 1265nm) and ES (around 1190nm) in the wholerange of pumping. Pulsed electrical pumping obtained from a high power (up to2A current) pulse source was used to achieve high output power operation. We simultaneously detect the total output and merely ES output using aBragg filter transmitting the short-wavelength and reflecting the long-wavelengthradiation. Typical QD does not demonstrate relaxation oscillations frequencybecause of the strong damping [2]. It is confirmed for the low (I 1.2 A) range of the pump currents in our experiments. The situationis different for a short range of the medium currents (0.68A

In recent years, quantum-dot (QD) semiconductor lasers attract significant interest in many practical applications due to their advantages such as high-power pulse generation because to the high gain efficiency. In this work, the pulse shape of an electrically pumped QD-laser under high current is analyzed. We find that the slow rise time of the pulsed pump may significantly affect the high intensity output pulse. It results in sharp power dropouts and deformation of the pulse profile. We address the effect to dynamical change of the phase-amplitude coupling in the proximity of the excited state (ES) threshold. Under 30ns pulse pumping, the output pulse shape strongly depends on pumping amplitude. At lower currents, which correspond to lasing in the ground state (GS), the pulse shape mimics that of the pump pulse. However, at higher currents the pulse shape becomes progressively unstable. The instability is greatest when in proximity to the secondary threshold which corresponds to the beginning of the ES lasing. After the slow rise stage, the output power sharply drops out. It is followed by a long-time power-off stage and large-scale amplitude fluctuations. We explain these observations by the dynamical change of the alpha-factor in the QD-laser and reveal the role of the slowly rising pumping processes in the pulse shaping and power dropouts at higher currents. The modeling is in very good agreement with the experimental observations.

We analyse strain-induced effects on the capacitance-voltage (C-V) profile for an MBE-grown GaAs/In0.1Ga0.9As/GaAs HFET structure. The calculations of C-V profile were made using a new small-signal approach developed for the quantum well (QW) structures. The self-consistent numerical simulations and results of measurements show that strain causes significant changes in the electron distribution of the QW structure and its C-V profile.

We investigate the Γ 2 -X z1 intersubband dynamics in GaAs/AlAs quantum-well structures by time-resolved infrared pump and probe experiments. In the studied structure, the second r level in GaAs is nearly resonant to the first X z level in AlAs. We observe bi-exponentially decaying signals with a short time constant of the order of 1 ps and a longer time constant of about 7 ps at 10 K and 4 ps at 300 K respectively. The long-term decay represents the X z -Γ 2 transfer by elastic Γ-X scattering at low temperatures. At 300 K electron-LO phonon scattering accelerates the Γ-X transfer.

The optical and structural properties of the Ge submonolayer nano-inclusions in a Si matrix grown by molecular beam epitaxy are investigated. It is shown that at relatively high growth temperatures >600° C new features appear in the photoluminescence spectra. It is found that these features correspond to formation of the germanium nano-inclusions in a silicon matrix.

Different types of microcavities for GaAs-based light emitting devices operating in the 1.3 µm spectral range are analysed. Microcavity light-emitting diodes (MC LEDs) can be fabricated with different designs of distributed Bragg reflectors (DBRs), e.g.: top and bottom AlAs/GaAs semiconductor DBRs; bottom AlAs/GaAs semiconductor and top dielectric DBRs; and oxidized AlxOy/GaAs DBRs. MC LEDs operating in the 1.3 µm spectral range and characterized by spectral width (13 nm) and narrow far-field pattern ( 40%) differential efficiency retained. A threshold current of

The low-temperature 2D variable range hopping conduction over the states of the upper Hubbard band is investigated in detail for the first time in multilayered Be-doped p-type GaAs/AlGaAs structures with quantum wells of 15-nm width. This situation was realized by doping the layer in the well and a barrier layer close to the well for the upper Hubbard band (A+ centers) in the equilibrium state filled with holes. The conduction was of the Mott hopping type in the entire temperature range (4−0.4 K). The positive and negative magnetoresistance branches as well as of non-Ohmic hopping conduction at low temperature are analyzed. The density of states and the localization radius, the scattering amplitude, and the number of scatterers in the upper Hubbard band are estimated. It is found that the interference pattern of phenomena associated with hopping conduction over the A+ band is qualitatively similar to the corresponding pattern for an ordinary impurity band, but the tunnel scattering is relatively weak.

High-resolution X-ray and synchrotron (crystal truncation rods) diffraction methods and transmission electron microscopy have been employed to study MBE-grown multilayer In(Ga)As-GaAs heterostructures with arrays of vertically coupled In(Ga)As quantum dots (QDs) in a GaAs matrix. Additional (vertical and lateral) spatial ordering of QDs in perfect crystalline structures, giving rise to undulations of the crystalline planes and quasi-periodic elastic strain, was shown to be essentially anisotropic with respect to crystallographic directions of the [110] type. The anisotropy of the QD formational system of can be accounted for by assuming that the spatial ordering of the QDs and the corrugation of the crystal planes are the initial stages of relaxation of the elastic strain introduced into the system by the QDs. The anisotropic relief of the crystal planes (corrugated growth surface) results from the formation of a system of spatially ordered quantum quasi-wires uniformly filled with QDs. In a multilayer heterostructure with high crystal perfection, the anisotropic relief of the crystal planes is inherited by overlying layers and its amplitude decreases gradually with increasing distance from the source of elastic strain—the superstructure containing In(Ga)As QDs in the given case.

Molecular beam epitaxy growth of InAs/InGaAs quantum dot (QD) structures on GaAs substrates for 1.3 μm laser applications is discussed. Long-stripe edge-emitting lasers demonstrate low threshold current density ( 2 ), high differential efficiency (>50%) and low internal loss (∼1–2 cm −1 ). Maximum output continuous-wave power for broad-area lasers is as high as 2.7 W. Narrow stripe (7 μm) lasers demonstrate single transverse mode operation with the maximum kink-free power of 110 mW. 1.3 μm vertical cavity surface emitting lasers were successfully fabricated from the structures with three QD planes inserted into the optical microcavity with AlO–GaAs Bragg reflectors. The output power is 220 mW at a drive current of 2.4 mA under pulsed mode for the device with the 8×8 μm oxidized aperture.

Various structures with optical microcavities and active layers based on InGaAs/GaAs quantum dots MBE-grown on GaAs substrates were studied theoretically and experimentally. LEDs for the 1.3 µm spectral range with narrow spectral characteristics and low light beam divergence were fabricated. Vertical lasing at 1.3 µm was obtained in a structure with oxidized AlO/GaAs mirrors under injection pumping.

Basic development steps towards the molecular beam epitaxy growth of AlGaAs/GaAs microcavity structures are presented, which contain self-organized InAs/GaInAs quantum dots as the active medium. The emission wavelength of these structures can be controllably adjusted within 1260–1340 nm by variation of the deposition parameters of the epitaxial layers without the use of any real-time monitoring technique. Based on quantum dot active material with optimized optical emission properties and accurately calibrated layer thicknesses microcavity light emitting diodes were fabricated. 40 μm diameter devices, as characterized on-wafer, showed narrow electroluminescence spectra (FWHM: 13–26 nm) centered at 1310–1325 nm and narrow circular beam widths of FWHM

Two designs of vertical-cavity surface-emitting lasers (VCSELs) for the 1.3 µm spectral range on GaAs substrates with active regions based on InAs/InGaAs quantum dots and InGaAsN quantum wells are considered. The relationship between the active region properties and optical microcavity parameters required for lasing has been investigated. A comparative analysis is made of VCSELs with active regions based on InAs/InGaAs quantum dots or on InGaAsN quantum wells, which are fabricated by MBE and demonstrate room-temperature CW operation. Optimization of the vertical microcavity design provides single-pass internal optical losses lower than 0.05%.

We have studied the dependence of hot electron scattering rate on temperature in n-GaAs/AlAs types I and II multiple quantum wells. For a sample with well width 37A, which is on the borderline between types I and II band alignment, the increase of the temperature in the range 6–80K leads to the strong decrease of the hot electron scattering rate. We explain this result by ionization of donors and transfer of cold electrons from the Γ-valley of GaAs to the X-valley of AlAs.

Experimental and theoretical study was made of injection lasers based on InAs/GaAs quantum dots (QDs) formed by the activated alloy phase separation and emitting at about 1.3 /spl mu/m. Electroluminescence and gain spectra were investigated. The maximum modal gain is measured experimentally using two different techniques. Threshold current densities as low as 22 A cm/sup -2/ per QD sheet were achieved. A step-like switch from ground- to excited-state transition lasing was observed with an increasing cavity loss. The characteristic temperatures for a sample with four cleaved sides and a 2-mm long stripe device at 300 K were 140 and 83 K, respectively. Single lateral-mode continuous-wave (CW) operation with the maximum output power of 210 mW was realized. Threshold characteristics of a laser were simulated taking into account radiative recombination in QDs, the wetting layer, and the optical confinement layer. The dependence of the threshold current density on the cavity length was shown to be extremely sensitive to the QD-array parameters determining the maximum gain for ground- and excited-state transitions and to the waveguide design. Our analysis reveals that nonradiative recombination channels may play an important role in the laser operation.

Optical and structural properties of heterostructures with InAs quantum dots overgrown by InGaAs quantum well and multilayer structures with InAs/GaAs quantum dots are investigated. Different growth techniques are used for the formation of an In-content region. It is shown that under optimal growth conditions, the 1.3 μm emission could be achieved for both type of structures. For multilayer structures, 1.4 μm emitting is achieved. Different scenarios of quantum dots multilayer structures evaluation are discussed in a frame of elastic theory to explain differences in the properties of the grown multilayer structures.

The Hall effect and electrical conductivity were studied in the temperature range of 1.7–300 K in Be-doped p-GaAs/AlGaAs multilayer structures with 15-nm-wide quantum wells. Doping of the well itself and the adjacent barrier layer was used to create a situation when the upper Hubbard band (the A + centers) was occupied with holes and electrical conduction proceeded over the states in this band. It is shown experimentally that the binding energy of A + centers increases significantly in the 15-nm-wide wells compared to this energy in the bulk, which is explained by the fact that the well size and the hole radius at the A + center are almost identical. The above radius was independently estimated from an analysis of the temperature dependence of the hopping conductivity.

New generation of long-wavelength (1.3 μm) GaAs based lasers is discussed. The modal gain, threshold current, quantum efficiency characteristics and temperature stability of lasers based on InGaAsn quantum wells and InAs/InGaAs quantum dots are compared.

(In)GaAsN epilayers were grown on GaAs substrates by molecular beam epitaxy (MBE) with a DC constricted-plasma source. Nitrogen incorporation efficiency, crystalline quality, surface morphology and luminescent properties of the epilayers were studied and correlated with various operation regimes of the source. The nitrogen incorporation efficiency grows with increasing plasma discharge current. The maximum nitrogen concentration in the epilayer is as high as 3.7 %. GaAsN as thick as 0.35 µm can be pseudomorphically grown on GaAs, and photoluminescence is observed at room temperature. The crystalline quality and surface morphology of an epilayer can also be improved by reducing the ion damage at low plasma discharge current. The DC constricted-plasma source is a promising alternative nitrogen plasma source for investigating InGaAsN materials.

We report on the emission of mid-infrared (MIR) radiation from InGaAs/AlGaAs quantum dots upon photoexcitation and electrical injection. Mid-infrared radiation is achieved from bipolar quantum-dot lasers during near-infrared lasing. The MIR spectrum exhibits a peak at 16 μm and is dominantly TM polarized. The MIR intensity exhibits a superlinear dependence on the injection. These results are compared to optically pumped emission from InGaAs/GaAs quantum dots. The unpolarized spectrum shows peaks at 15 and 10 μm. The MIR intensity increases sublinearly with excitation power.

Semiconductor heterostructures with size quantization of carriers in all three directions, or quantum dots (QDs), open a new era in device engineering. An important breakthrough occurred when the self-organised growth approach had been refined to such an extent, that defect-free QDs made with these technique exhibited properties predicted for zero-dimensional structures. Their practical application in devices, first of all lasers, became possible. When used for active layers in injection lasers differential gain is strongly increased potentially providing improved dynamic properties. The cut-off frequencies larger than 10 GHz are presently demonstrated. The saturation material gain is as high as 15 x 10 4 cm -1 as compared to QW values of about 3 x 10 3 cm -1 , The wavelength dependence of gain is best described by Master equations of microstates. High internal (>96%) and differential (70%) efficiencies at 300 K and output power up to 4 W are realized now for QD lasers emitting in the 0.94-1.15 μm range. Transparency current density of 18 A/cm 2 has been recently demonstrated at 1.15 μm. GaAs-based QD lasers emit near 1.3 μm with J th = 70 A/cm 2 (L = 1.9 mm, 300 K) and CW output power of ∼3 W. In narrow (7 μm) stripes almost chirp-free operation and relaxation oscillations at 2.4 GHz (L = 400 μm) are manifested. Differential efficiency is 55% and internal losses are 1.5 cm -1 . 1.3 μm GaAs-based QD VCSELs (300 K, I th = 1.8 mA, η diff > 40%) are realized.

AlGaAs/GaAs microcavity structures with InAs/InGaAs quantum dot (QD) active regions were grown by molecular beam epitaxy (MBE) on GaAs substrates and their optical characteristics were studied. Methods for the optimization of optical emission properties of the InAs/InGaAs QDs and accurate calibration of the proper layer thickness are discussed. Microcavity light-emitting diodes (MC-LEDs) with a QD active region demonstrate narrow electroluminescence (EL) spectra (FWHM < 15 nm) accompanied by an output beam divergence of only 17°. The MC-LED emission wavelength can be controllably changed by varying the QD material composition in combination with tuning the optical microcavity.

Microcavity structures containing InGaAs-GaAs quantum dots (QDs) emitting at 1.3 μm at 300 K have been studied. The angle-resolved photoluminescence measurements revealed a large spectral splitting of TE and TM components, which amounts up to 12 nm for an angle of emission of 30°. This effect is tentatively explained by diffraction of the electro-magnetic field at a single anisotropically shaped QD and the collective effect of the anisotropy of the QD array.

Metastable quantum dot (QD) arrays were grown by submonolayer migration enhanced epitaxy (SMEE) mode on GaAs(100) singular and vicinal substrates. It has been established that two QD groups are formed on the vicinal surface. These groups – conjunct QDs (CQD) and isolated QDs (IQD) – demonstrate a basically different behavior in their photoluminescence spectra. The CQDs form chain-like structures. They lay on the wetting layer which connects them to each other. The IQDs are formed due to wetting layer rupture directly on the GaAs surface at the terrace edges. They are isolated and not connected to the rest QD array.

We have studied the dynamical population of discrete energy levels by spin-polarized electrons in self-assembled quantum dots (QDs) InAs/GaAs. We report on the observation of the electron mean spin redistribution over the energy spectrum of a QD as a result of Pauli blocking. The electron polarization is determined by measuring the degree of circular polarization of the QD emission after excitation by circular polarized light pulses in the GaAs barrier. A theoretical model is developed that qualitatively describes isolated as well as coupled QDs.

MBE growth and properties of InAs nanoscale islands formed on silicon are reported. Islands capped with Si emit a photoluminescence band in the 1.3 mm region. Upon annealing at increased substrate temperature, extensive interdiffusion leads to the formation of an InAs solid solution in the Si cap layer. Additionally, InAs-enriched regions with extensions of 6n m, exhibiting two kinds of ordering, are observed. The ordering of InAs molecules occurs, respectively, in (101) and (101( ) planes inclined to (110) and (11( 0) planes parallel to the [001] growth direction. © 2001 Elsevier Science B.V. All rights reserved.

Finite-temperature thermodynamic theory is developed for equilibrium arrays of two-dimensional monolayer-high islands in heteroepitaxial systems at submonolayer coverage. It is shown that the entropy contribution to the Helmholtz free energy of the system favors formation of smaller islands at higher temperatures which results in a decrease of the average number of atoms in the islands (the island volume) with temperature. The characteristic temperature T char , at which the island volume is significantly decreased compared to its value at T = 0 K, is found to be far below the characteristic energy of the island formation and to lie in a region of several hundreds of K. Such a temperature dependence can be the basis for decisive experiments aimed at distinguishing between thermodynamic and kinetic effects in the formation of arrays of 2D islands. Results of high resolution electron microscopy and photoluminescence spectroscopy of a submonolayer InAs/GaAs(001) system are in agreement with the theory. It confirms that the formation of a sub-monolayer array of InAs/GaAs(001) islands is predominantly influenced by thermodynamics.

This paper summarizes experimental results on MBE-grown InAs/Si-based quantum-size quantum-dot heterostructures fabricated in the Institute of Analytical Instrument Making, Russian Academy of Sciences, and the Ioffe Physicotechnical Institute, Russian Academy of Sciences. The structures were examined by the reflection high-energy electron diffraction (RHEED) and photoluminescence (PL) methods, as well as by STM, SEM, and TEM techniques. The aim of works under way is to integrate III–V and silicon technologies for the production of new-generation optoelectronic and microelectronic devices.

The optical anisotropy of InAs quantum dots (QDs) synthesized in the regime of either continuous or submonolayer deposition on a singular GaAs(100) surface have been studied using polarized photoluminescence measurements. It is established that an isolated array of QDs formed in a continuous deposition regime possesses a weak (

Optical and structural properties of multilayer structures with InAs/GaAs quantum dots are investigated. It is shown that under optimal growth conditions, 1.3-1.4 µm emission can be achieved. Possible scenarios of quantum dot behaviour evaluation are discussed in a frame of elastic theory to explain differences in optical properties of the grown structures.

An experimental study of carrier relaxation mechanisms and carrier distribution in InAs-InGaAs-GaAs quantum dot (QD) arrays is presented. The structures were investigated by resonant photoluminescence (PL) at different temperatures. For a sample with low confinement energy for electrons and holes in a QD the carrier distribution within the QD array changes from non-Fermi (random) to Fermi (equilibrium) when temperature increases from 20 to 300 K. In contrast, for the sample with high QD confinement energy the carrier distribution remains random even at room temperature. Near-resonant PL at 20 K reveals a series of broad phonon replicas ascribed to multiphonon relaxation processes involving LO phonons in the QD, in the wetting layer, at the interface and in GaAs as well as acoustic phonons. The complex distribution of InGaAs in QDs formed by activated alloy phase separation is believed to cause a dispersion of QD phonon energies and to lead to a further broadening of phonon lines.

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.

A comparative analysis is made of laser diodes based on Stranski-Krastanow (SK) and sub-monolayer (SML) InAs/GaAs quantum dots, emitting at about 940 nm. Owing to the better uniformity of sub-monolayer quantum dots, the SML QD laser surpasses the SK QD one in power characteristics. A maximum output power of 3.9 W and a peak power conversion efficiency of 59% have been achieved for SML QD 100 µm wide lasers at 10 °C.

Polarized electron emission from a series of new strained short-period AlInGaAs/AlGaAs superlattices (SLs) is investigated. The In layer content was chosen to give minimal conduction band offset with large strain splitting of the V-band. Simultaneous changing of Al content in both SL layers provides variation of the structure band gap. We demonstrate that tuning of the SL to the excitation energy can be achieved without loss of the electron polarization. The polarization of up to 84% was measured at room temperature.

The possibility of obtaining a new nanostructured material, an InSiAs solid solution, by molecular beam epitaxy on the Si(001) surface is reported. It is demonstrated that, during simultaneous deposition of indium, silicon, and arsenic, nanometer-size islands with a rectangular base and the sides oriented along the {110} directions can form when the layer thickness exceeds 35 nm. After depositing a 100 nm thick layer of the solid solution, islands with the side ratio \(d_{110} /d_{1\bar 10} = 1.35\) and a typical lateral size of \(d_{1\bar 10} \sim 35 \pm 10\) nm are obtained.

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".

Data are presented on the threshold and power characteristics and their dependence on the quantum dot (QD) surface density for QD diode lasers. The active region is based on the dense array of composite InAs/InAlAs self-organized QDs. The 3.5 W output power, limited by catastrophic optical damage, and a peak conversion efficiency of 45% were achieved at 10°C in 100-μm-wide diodes with uncoated facets.

We have studied quantum dots (QDs) fabricated by activated spinodal decomposition (ASD) of an InGa(Al)As alloy deposited on top of self-organized InAs nanoscale stressors on GaAs substrate. Such a growth sequence results in a strong red shift of the PL emission down to 1.3 μm at 300 K. This red shift is caused by the formation of In-rich areas in the vicinity of the InAs islands, which increase the effective dot size. Beyond a certain critical InAs composition or nominal thickness of the InGa(Al)As layer the PL line shifts back towards higher energies. Adding Al to the alloy increases the red shift for a given In concentration. Room temperature lasing near 1.3 μm with threshold current densities of about 85 A / cm 2 was achieved for lasers based on three-fold stacked ASD-formed QDs, with a maximum cw output power of 2.7 W.

Microcavity structures containing InGaAs-GaAs quantum dots (QDs) emitting at 1.3µm at 300 K have been studied. The energy distribution of excitons remains an nonequilibrium one up to room temperature due to high localization energies in these QDs. Carrier relaxation is found to proceed mainly via multiphonon processes. The luminescence emission from QDs in a microcavity exhibits a large spectral splitting of TE and TM components as observed in angle-resolved measurements amounting up to 10 nm for an angle of incidence of 30°. A 1.3 µm vertical cavity enhanced QD photodetector based on a single sheet of QDs is shown to have a quantum efficiency >10%. The ground state electroluminescence of a quantum dot resonant cavity light emitting diode shows no saturation up to 2 kAcm−2.

We report on the observation of miniband transport in a GaAs/AlAs superlattice with AlAs barrier layers of submonolayer thickness. The current–voltage characteristic of the superlattice at static electric fields showed a negative differential conductance, which is related to miniband electrons performing Bloch oscillations. Under the influence of a THz field, the current through the superlattice was reduced due to a dynamic localisation of the miniband electrons. Our results showed that the novel superlattice can be used as THz detector with a dynamic range of six orders of magnitude and with a responsivity of 0.2 V/W.

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.