A. Yu. Andreev

High-power laser diodes (λ = 808–850 nm) based on asymmetric separate-confinement heterostructures

Symmetric and asymmetric separate-confinement AlGaAs/GaAs heterostructures have been grown by MOCVD in accordance with the concept of design of high-power semiconductor lasers. High-power laser diodes with a 100-µm aperture, emitting in the 808–850-nm range, were fabricated from these structures. The internal optical loss in asymmetric separate-confinement heterostructures with broadened waveguide is reduced to 0.5 cm−1. In the lasers with 1.7-µm-thick waveguide, the output optical power of 7.5 W in CW mode was achieved owing to reduction of the optical emission density at the cavity mirror to 4 mW/cm2.

High-power lasers (γ = 808 nm) based on the AlGaAs/GaAs heterostructures of separate confinement

Laser diodes with a wavelength of 808 nm obtained by the MOC-hydride epitaxy in a system of the AlGaAs alloys have been studied. Parameters of the laser diodes with symmetric narrow and asymmetric wide waveguides are compared. It is shown that the maximum optical power in these laser diodes is limited by the catastrophic optical degradation of the SiO2/Si mirrors. In laser diodes with a symmetric narrow waveguide, the maximum power was 3 W, and with an asymmetric wide waveguide, it was 6 W. It is shown that it is possible to increase the maximum optical power by using the barrier Si3N4 layer introduced between the cleavage of the laser diode and SiO2/Si insulator coatings. The power of a laser diode with the barrier Si3N4 layer and with the asymmetric wide waveguide was 8.5 W.

Cosmological parameters and the large numbers of Eddington and Dirac

Cosmological large numbers are studied using dimensional analysis. Expressions linking cosmological parameters with fundamental constants of the microworld are proposed. The Zel’dovich formula for the cosmological constant is generalized, and a series of characteristic masses of the Universe is derived.

Optically active layers of silicon doped with erbium during sublimation molecular-beam epitaxy

A study is made of the electrical, optical, and structural properties of Si:Er layers produced by sublimation molecular-beam epitaxy. The Er and O contents in the layers, grown at 400–600°C, were as high as 5×1018 and 4×1019 cm−3, respectively. The electron concentration at 300 K was ∼10% of the total erbium concentration and the electron mobility was as high as 550 cm2/(V·s). Intense photoluminescence at 1.537 µm was observed from all the structures up to 100–140 K. The structure of the optically active centers associated with Er depended on the conditions under which the layers were grown.

Quantum cascade laser based on GaAs/Al0.45Ga0.55As heteropair grown by MOCVD

A pulsed quantum cascade laser emitting in the wavelength range 9.5–9.7 μm at 77.4 K is developed based on the GaAs/Al0.45Ga0.55As heteropair. The laser heterostructure was grown by MOCVD. The threshold current density was 1.8 kA cm-2. The maximum output power of the laser with dimensions of 30 μm × 3 mm and with cleaved mirrors exceeded 200 mW.

Dynamics of the formation of an event horizon

The radial motion of matter in a gravitational field with a symmetry center in a comoving reference frame is investigated for a realistic equation of state of matter. The dynamics of the formation of an event horizon is investigated.

Metalorganic vapour phase epitaxy of GaAs/AlGaAs nanoheterostructures for a quantum cascade laser

Short-period GaAs/AlGaAs superlattices, an active region, and a quantum cascade laser heterostructure have been grown by metalorganic vapor phase epitaxy, and their characteristics have been studied by high-resolution X-ray diffraction, transmission electron microscopy, and photoluminescence spectroscopy. The heterostructures have been used to produce quantum cascade lasers emitting near 10 μm. Their output pulse power at 77 K is above 200 mW.

Quantum cascade laser grown by MOCVD and operating at 9,7 μm

A quantum cascade laser emitting in the spectral range of 9.7 μm at 77 K has been developed. The laser heterostructure based on GaAs/AlGaAs was grown by the MOCVD technology. In the pulsed operation mode, the threshold current density of ~2 kA/cm2 and the emission power of above 200 mW have been obtained for the laser of the dimensions of 30 μm × 3 mm.

Laser emitters (λ = 808 nm) based on AlGaAs/GaAs heterostructures

AlGaAs/GaAs laser heterostructures with various active-region geometries, namely, with broadened asymmetric and narrow symmetric waveguides, and with various depths of quantum wells, are obtained by MOC hydride epitaxy. Single laser elements, bars, and arrays of laser diodes are fabricated from these samples, and their output characteristics are investigated. It is shown that the geometry of the narrow-waveguide structure is more preferable for laser-diode bars (λ = 808 nm). Increasing the charge-carrier barrier also favorably affects the output parameters of the bars in the case of heterostructures with a narrow symmetric waveguide, and the slope of the power-current (P-I) characteristics for these structures increases from 0.9 W/A to 1.05 W/A. The laser diode array of 5 × 5 mm, which is assembled based on the best heterostructure, shows an output power above 1500 W in the quasi-continuous mode at a pump current of 150 A.

Influence of segregation effects on the electroluminescence spectra of InGaAs/GaAs quantum well heterostructures grown by H-MOVPE

Surface segregation during epitaxial growth of stressed InGaAs/GaAs quantum-well heterostructures significantly distorts the nominal concentration profile of quantum wells. The consideration of the effect for growth conditions and elastic stresses appearing during epitaxy on segregation made it possible to simulate the concentration profile with a high accuracy and to calculate the electroluminescence wavelength of actual InGaAs/GaAs heterostructures with quantum wells. It was shown that the observed effect of the long-wave-length shift for the interband transition wavelength in the important case of heterostructures with two neighboring quantum wells is caused by the influence of elastic stresses during growth.