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A method for extracting silicon isotopes was developed. Polycrystalline 28Si, 29Si, and 30Si samples isotopically enriched to 99.95, 99.5, and 99.9%, respectively, were prepared. Energies of optical phonons in the isotopically pure samples show the expected dependence on the average atomic mass.

We study optical properties of ZnMgSSe‐ZnCdSe structures with CdSe submonolayers inserted in a ZnSe matrix. Remarkably high exciton oscillator strength is found in ultrashort‐period submonolayer CdSe‐ZnSe superlattices, as compared to ZnCdSe quantum wells of comparable average width and Cd composition. In conventional ZnCdSe quantum wells the lasing occurs at energies ∼30 meV below the free heavy‐hole exciton transition revealed in photoluminescence and in optical reflectance spectra. In the CdSe submonolayer superlattices lasing occurs at energies in the very vicinity of the heavy hole exciton resonance, directly in the region of strongly‐enhanced exciton‐induced modulation of the reflectance spectrum, and, consequently, refractive index change. We attribute the effects observed to exciton localization by potential fluctuations caused by nanoscale CdSe islands formed during submonolayer deposition.

An InAs quantum dot (QD) array covered by a thin InGaAs layer was used as the active region of diode lasers grown by molecular beam epitaxy on GaAs substrates. The wavelength of the ground-state transition in such heterostructures is in the 1.3 μm range. In the laser based on the single layer of QDs, lasing proceeds via the excited states due to insufficient gain of the ground level. Stacking of three QD planes prevents gain saturation and results in a low threshold (85 A/cm2 in broad-area 1.9-mm-long stripe) long-wavelength (1.25 μm) lasing at room temperature via the QD ground state with relatively high differential efficiency (>50%).

The relaxation mechanisms of an array of 10 vertically coupled layers of InGaAs/AlGaAs quantum dots were studied by time-resolved photoluminescence. Both resonant and non-resonant excitation were employed and the photoluminescence (PL) intensity in the non-resonant case is a factor of 200 larger than the intensity with resonant excitation. The results obtained in the non-resonant pumping experiment were analysed with a rate equation model. It was found that the PL decay time increases rapidly with the wavelength of detection. Large carrier capture cross-sections [(2.5±0.9)×10-5 cm3/s] were deduced, resulting in a capture time of 1 ps for a carrier concentration of 4×1016 cm-3. A very fast PL risetime was observed with resonant pumping, ruling out a phonon bottleneck effect in these samples. The decay times at a given wavelength are always shorter for resonant than for non-resonant excitation and their difference increases rapidly with wavelength. This is interpreted in terms of a state filling effect for the non-resonant case.

Structural and optical properties of structures with nanoscale InAs islands obtained by submonolayer deposition and embedded in an AlxGa1−xAs matrix is investigated. Deposition of several planes of InAs insertions results in formation of arrays of vertically correlated islands. The lateral size of the islands in a column is about 10 nm. Lasing via the ground states of the islands without external optical confinement is demonstrated.

The ground-state (GS) exciton transition is revealed in optical reflectance and photoluminescence (PL) spectra of structures with multiple sheets of nanoscale islands formed by submonolayer CdSe insertions in a ZnMgSSe matrix. The GS transition is absent, however, in the PL excitation (PLE) spectra, demonstrating a typical quantum dot-like PLE behavior. High exciton oscillator strength and lifted k-selection rule caused by exciton confinement permits room temperature zero-phonon lasing (460 nm) resonant to the spectral region of exciton-induced refractive index (n) enhancement without using thick cladding layers having a lower n.

InSb nanoislands in a GaSb matrix have been fabricated and their structural and luminescence properties have been studied. The deposition of ∼2 monolayers of InSb on the GaSb(100) surface has been found by atomic force microscopy to result in a 2D–3D growth mode transition and in a formation of 3D InSb islands with a size about 80 nm. Increase in the thickness of the InSb layer more than three monolayers causes a dramatic drop of the photoluminescence intensity due to plastical relaxation of the islands. Surprisingly transmission electron microscopy studies of InSb insertions with average InSb thickness below two monolayers demonstrate dense array of coherent 2D islands, or quantum dots, having a uniform lateral size of 30 nm. Bright luminescence due to these 2D islands is observed. We believe that these 2D multimonolayer islands can be used as precursor state for vertically coupled InSb-GaSb QD structures suitable for laser applications.

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.

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.

We report design, MBE growth and optical studies of optically dense, strained ZnSSe/ZnCdSe multiple quantum wells (MQWs) and superlattices (SLs). To avoid stress relaxation in the thick multilayer structures, particular attention is paid to the accurate design of alternating compressive and tensile stress in the constituent layers. The feasibility of using the alternatively strained SLs and MQWs as the guide and active regions of optically pumped MgZnSSe/ZnCdSe blue-green lasers is experimentally confirmed. A room-temperature threshold power density as low as 20 kW/cm 2 has been achieved at 490 nm in conventional waveguide-geometry lasers with a SL guide layer. A room-temperature optically pumped vertical-cavity laser utilizing a long ZnSSe/ZnCdSe MQW active region and a short external cavity is demonstrated.

Quantum dot (QD) structures are believed to provide a promising way for a new generation of injection lasers. Intrinsic properties of QD lasers such as strongly increased gain and differential gain, ultra low threshold current density and high characteristic temperature are theoretically predicted. Some of these characteristics are experimentally verified at liquid nitrogen temperatures on realistic device structures. Due to small dot densities in the range of 5/spl times/10/sup 10/ cm/sup -2/ single layer quantum dot (SLQD) lasers exhibit a very small confinement factor and thus lack the ability to serve as high power lasers. The dot density within the active region can be increased by stacking the dot layers vertically on top of each other. The threshold current behaviour of a stacked QD laser is compared with that of a single layer QD laser. We demonstrate for the first time room temperature lasing of a stacked QD laser via the QD ground state.

Injection lasers based on InAs-GaAs and InGaAs-GaAs quantum pyramids (QPs) with a lateral size ranging from 80 to 140 A are realized. The structures with relatively small dots (80 A) exhibit properties predicted earlier for quantum dot (QD) lasers such as low threshold current densities (below 100 A cm -2 ) and ultrahigh characteristic temperatures (To = 350 to 425 K). For temperatures of operation above 100 to 130 K T 0 decreases and the threshold current density increases (up to 0.95 to 3.3 kA cm -2 at room temperature) due to carrier evaporation front QPs. Larger InAs QPs (140 A) providing better carrier localization exhibit saturation of the ground state emission and enhanced nonradiative recombination rate at high excitation densities. The radiative lifetime shows a weak dependence on the dot size (80 to 140 A) being close to 1.8 to 2 ns. respectively. A significant decrease in radiative lifetime is realized in vertically-coupled quantum clots formed by a QP shape-transformation effect. The final arrangement represents a three-dimensional tetragonal array of InAs islands inserted in a GaAs matrix each composed of several vertically merging InAs parts. The first injection lasing in such an array is achieved.

Molecular-beam epitaxy with a solid source was used to grow silicon layers enriched with 28Si and 30Si isotopes to 99.93 and 99.34%, respectively. Secondary-ion mass spectrometry and Raman scattering spectroscopy were applied to demonstrate the high isotopic purity and crystal perfection of the layers obtained.

Photoluminescence and capacitance–voltage studies of modulation doped equilibrium quantum dots (QDs) formed by a 4ML InAs deposition in a GaAs matrix by molecular beam epitaxy have been performed. Two electron states are revealed in the n-type modulation-doped structures: due to QDs and due to InAs wetting layer. For the p-type modulation doped QDs the PL peak is shifted to higher energies due to high concentration of holes in a QD, there exist also a significant shift in the characteristic energy for the efficient excitation of the QD ground state, as compared to undoped QDs, which we attribute to the filling of the valence band sublevels with equilibrium holes.

Electronic transitions in nm-scale pyramid-shaped InAs/GaAs quantum dots feature only ground-state electrons. Allowed optical transitions involving excited hole states in addition to the ground-state transition are revealed in absorption and photoluminescence spectra. The experimental data agree with detailed theoretical calculations of the electronic structure, including strain, piezoelectric, and excitonic effects, and lead to unambiguous assignment of the transitions. We find as upper bound for the relative standard deviation of the size fluctuation $\ensuremath{\xi}l~0.04$. The hole sublevel separation is consistent with a pyramid shape fluctuation between {101} and {203} side facets.

A 2-km fiber-optical telecommunication line was investigated. Specially developed new semiconductor heterolasers, emitting at the wavelength of 1.3 μ, and low-loss optical fibers were used in this line. The energy characteristics of the new lasers were found to be suitable for data transmission over tens of kilometers.