P.S. Kop'ev

InGaAs-GaAs quantum-dot lasers

Quantum-dot (QD) lasers provide superior lasing characteristics compared to quantum-well (QW) and QW wire lasers due to their delta like density of states. Record threshold current densities of 40 A/spl middot/cm/sup -2/ at 77 K and of 62 A/spl middot/cm/sup -2/ at 300 K are obtained while a characteristic temperature of 385 K is maintained up to 300 K. The internal quantum efficiency approaches values of /spl sim/80 %. Currently, operating QD lasers show broad-gain spectra with full-width at half-maximum (FWHM) up to /spl sim/50 meV, ultrahigh material gain of /spl sim/10/sup 5/ cm/sup -1/, differential gain of /spl sim/10/sup -13/ cm/sup 2/ and strong nonlinear gain effects with a gain compression coefficient of /spl sim/10/sup -16/ cm/sup 3/. The modulation bandwidth is limited by nonlinear gain effects but can be increased by careful choice of the energy difference between QD and barrier states. The linewidth enhancement factor is /spl sim/0.5. The InGaAs-GaAs QD emission can be tuned between 0.95 /spl mu/m and 1.37 /spl mu/m at 300 K.

Mie Resonances, Infrared Emission, and the Band Gap of InN

Mie resonances due to scattering or absorption of light in InN-containing clusters of metallic In may have been erroneously interpreted as the infrared band gap absorption in tens of papers. Here we show by direct thermally detected optical absorption measurements that the true band gap of InN is markedly wider than the currently accepted 0.7 eV. Microcathodoluminescence studies complemented by the imaging of metallic In have shown that bright infrared emission at 0.7-0.8 eV arises in a close vicinity of In inclusions and is likely associated with surface states at the metal/InN interfaces.

InAs–GaAs Quantum Pyramid Lasers: In Situ Growth, Radiative Lifetimes and Polarization Properties

We have realized injection lasers based on InAs–GaAs and InGaAs–GaAs quantum pyramids (QPs) with a lateral size ranging from 80 to 140 A. 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 Acm-2) and ultrahigh characteristic temperatures (T0=350–425 K). For operation temperatures above 100–130 K, T0 decreases and the threshold current density increases (up to 0.95–3.3 kAcm-2 at room temperature) due to carrier evaporation from 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 in the range 80–140 A being close to ~1.8–2 ns, respectively. A significant decrease in radiative lifetime is realized in vertically coupled quantum dots formed by a QP shape-transformation effect. The final arrangement corresponds to a three-dimensional tetragonal array of InAs islands inserted in a GaAs matrix each composed of several vertically merging InAs parts. We achieved injection lasing in such an array for the first time.

Continuous-wave operation of long-wavelength quantum-dot diode laser on a GaAs substrate

Continuous-wave operation near 1.3 /spl mu/m or a diode laser based on self-organized quantum dots (QDs) 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.

Self-organization processes in MBE-grown quantum dot structures

InAs quantum dots in a GaAs matrix have been prepared by molecular beam epitaxy using a self-organizing mechanism. A narrow size distribution of single dots of pyramidal shape (typically with a base of 12 ± 1 nm and a height of 4–6 nm) is created as directly imaged with plan-view and cross-section transmission electron microscopy. The dots exhibit self-organized short range order and preferentially align in rows along 〈100〉. The photoluminescence of the dot ensemble has, due to fluctuations in dot size, shape and strain, a FWHM of typically 50–60 meV. However, using highly spatially and spectrally resolved cathodoluminescence it is possible to directly excite a tiny fraction of all dots (typically only 30 dots). Under these excitation conditions the spectrum changes drastically into a series of ultrasharp lines with a FWHM < 0.15 meV, each originating from a different single InAs quantum dot. This directly visualizes their δ function-like density of electronic states, especially since the lines remain sharp even for kBT⪢FWHM.

Low-threshold injection lasers based on vertically coupled quantum dots

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.

Exciton longitudinal-transverse splitting in GaAs/AlGaAs superlattices and multiple quantum wells

Abstract The exciton longitudinal-transverse splitting,ωLT, has been investigated both theoretically and experimentally in periodic GaAs/AlGaAs heterostructures. It has been shown that the 2D-3D transition manifests itself in the ωLT dependence on the SL period, (Lz + Lb), more dramatically than in the exciton binding energy dependence on the period.

Composition stoichiometry and growth rate control in molecular beam epitaxy of ZnSe based ternary and quaternary alloys

Abstract This paper presents an original thermodynamic description of (Mg,Zn)(S,Se) MBE growth, which is in a good quantitative agreement with experimental data. This approach provides large flexibility in choosing different growth regimes of pseudomorphic ZnSe-based heterostructures to obtain desirable alloy composition, surface stoichiometry, and growth rate. The possibility to control a nearly lattice-matched to GaAs composition of a Zn1−xMgxSySe1−y alloy from (x = 0, y = 0.09) to (x = 0.07, y = 0.13) only by variation of the Mg flux intensity has been theoretically revealed and experimentally realized in an optically pumped ZnMgSSe/ZnSSe/ZnCdSe SQW SCH laser structure with a threshold power density of 20 kW/cm2 at 300 K.

Formation of InAs quantum dots on a silicon (100) surface

At moderate arsenic fluxes and substrate temperatures (470 ) InAs grows on Si (100) surface in the Stranski-Krastanow growth mode with the formation of mesoscopic dislocated clusters on top of a two-dimensional periodically corrugated InAs wetting layer. In contrast, at lower temperatures (250 ) a dense array of self-organized nanoscale InAs quantum dots of uniform size and shape is formed. These quantum dots, when grown on a Si buffer layer and covered with a Si cap, give a luminescence line at about 1.3 m.

Molecular beam epitaxy growth and characterization of thin (<2 mu m) GaSb layers on GaAs(100) substrates

This paper reports the effect of growth parameters and buffer structure on the luminescence electrical and structural characteristics of thin (<2 mu m) GaSb layers grown by molecular beam epitaxy (MBE) on GaAs(100) substrates. A two-stage substrate temperature growth regime has been developed on the basis of a thermodynamic consideration of the growth process, taking into account the additional Gibbs free energy due to the strain at the initial growth. This regime permits the growth of GaSb epilayers with a small Sb/Ga ratio at high substrate temperatures; it provides a greater exciton photoluminescence (PL) intensity and Hall mobility (over 5000 cm2 V-1 s-1 at 77 K) and improves the layer quality. The appearance of a free exciton luminescence line (809 meV) in the PL spectra of MBE GaSb/GaAs is reported for the first time. It is also shown that a (50 AA AlSb/50 AA GaSb)10 short-period superlattice prevents non-radiative recombination centres and carrier scattering centres from propagating in the top GaSb layer but does not bend the misfit dislocation growing through the layer from the GaSb/GaAs interface.