A. A. Marmalyuk

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.

On the Possibility of Growth Quantum Dot Arrays in InAs/GaAs System by Droplet Epitaxy under MOVPE Conditions

We have experimentally studied the possibility of obtaining InAs quantum dot arrays on GaAs(100) substrates by droplet-island growth under low-temperature (160–360°C) metalorganic vapor phase epitaxy (MOVPE) conditions. It is established that trimethylindium (In source) exhibits decomposition even at the lower boundary of the indicated temperature interval. The height of In drops formed on the substrate surface was 3–12 nm with a density of ∼(0.4−1.4) × 109 cm−2 depending on the H-MOVPE conditions. In order to retain the dimensions of InAs nanocrystals formed at the subsequent stage, the process should be carried out at an increased rate of arsine supply.

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.

Physicochemical aspects of quantum dot array formation in the InAs/GaAs system by droplet epitaxy under MOVPE conditions

Conditions of the deposition of indium droplets on GaAs(100) substrates during low-temperature (100°C) decomposition of trimethylindium have been studied. It is established that, in order to eliminate the partial coalescence of the indium droplets, it is possible to use subsequent heat treatment for evaporating excess indium. The heat treatment at a temperature of 350–500°C, only slightly modifies the composition of indium drops as a result of the substrate solution and, hence, does not significantly change the composition of quantum dots grown in this system.

The temperature dependence of internal optical losses in semiconductor lasers (λ = 900-920 nm)

The temperature dependences of radiative characteristics of semiconductor lasers based on asymmetric heterostructures of the separate confinement with an extended waveguide fabricated by MOCVD epitaxy (the emission wavelength λ = 900–920 nm) are studied. It is established that the threshold concentration in the active region and waveguide layers of the laser heterostructure of the separate confinement increases in the CW lasing mode as the pumping current and temperature of the active region are increased. It is established experimentally that, in the temperature range of 20–140°C, the stimulated quantum yield remains unchanged. It is shown that the temperature delocalization of charge carriers leads to an increase in the carrier concentration in the waveguide layers of the laser heterostructure. The total increase in internal optical losses due to scattering by free charge carriers in the layers of the active region and waveguide layers of the laser heterostructure leads to a decrease in the differential quantum efficiency and to saturation of the watt-ampere characteristic of semiconductor lasers in the continuous lasing mode.

Laser diodes with several emitting regions (λ = 800–1100 nm) on the basis of epitaxially integrated heterostructures

The results of a series of studies concerned with formation of epitaxially integrated InGaAs/AlGaAs and AlGaAs/AlGaAs heterostructures with several emitting regions and with investigation of properties of laser diodes based on the above structures operating in the spectral ranges λ = 800–810, 890–910, and 1040–1060 nm are summarized. It is shown that the suggested approach to integration of individual laser structures by the method of the MOVPE epitaxy operates efficiently in fabrication of laser diodes for a wide spectral range on the basis of various types of heterostructures. This approach made it possible to efficiently increase the output power of the laser diodes practically without variation in their mass-and-dimension characteristics. The main advantages of this approach and its limitations are outlined. Epitaxial integration of two laser heterostructures made it possible to increase the differential quantum efficiency by 1.7–2.0 times, while integration of three laser heterostructures increases the differential quantum efficiency by a factor of 2.5–3.0.

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.

Formation conditions for InAs/GaAs quantum dot arrays by droplet epitaxy under MOVPE conditions

The first stage of formation of InAs/GaAs quantum-dot heterostructures by droplet epitaxy is investigated. Factors influencing the geometrical size and density of arrays of indium nanodrops deposited by trimethylindium pyrolysis on the GaAs(100) substrate are analyzed, and the possibility of using these factors in the process of metal-organic vapor phase epitaxy (MOVPE) are studied. To refine the temperature dependence of the In evaporation rate, a computational experiment taking into account real MOVPE conditions is conducted. An ultimate change in the composition of In droplets contacting the substrate at a high temperature is estimated, and the thickness and composition of crystallizing In-Ga-As solid solution are calculated. It is shown that the size and density of the droplet array to a great extent depend on the crystallochemical structure of the substrate surface and deposition conditions.

Laser-diode arrays based on epitaxial integrated heterostructures with increased power and brightness of the pulse emission

The results of studying single laser diodes and arrays in the spectral range of 900–1060 nm, fabricated based on InGaAs/AlGaAs epitaxially integrated heterostructures are presented. It is shown that the use of InGaAs/AlGaAs epitaxially integrated heterostructures allows the development of laser emitters with increased power and brightness, operating in the short pulse mode. The results of studying the characteristics of laser-diode arrays (LDAs) fabricated using these heterostructures are presented.

Simulation of the indium profile in InGaAs/GaAs quantum-size heterostructures

A new approach to describe phenomena attendant on the growth of thin InGaAs epitaxial layers by hydride MOCVD in terms of which the boundary gas layer is considered as quasi-liquid is suggested. A numerical model for simulating the concentration profiles of the components in quantum-well heterostructures is developed. It is based on the assumption that a state close to thermodynamic equilibrium exists near the interface. The concentration profiles are simulated by jointly solving equations that describe heterogeneous equilibria and material balance at the interface. The indium profiles in InGaAs/GaAs quantum-size heterostructures are simulated at various parameters of the epitaxy process, such as temperature, initial component ratio in the gas phase, and boundary layer thickness. The results obtained agree well with the available experimental data.