A. V. Murashova

High-Power Laser Diodes Based on Asymmetric Separate-Confinement Heterostructures

Asymmetric separate-confinement laser heterostructures with ultrawide waveguides based on AlGaAs/GaAs/InGaAs solid solutions, with an emission wavelength of ∼1080 nm, are grown by MOCVD. The optical and electrical properties of mesa-stripe lasers with a stripe width of ∼100 μm are studied. Lasers based on asymmetric heterostructures with ultrawide (>1 μm) waveguides demonstrate lasing in the fundamental transverse mode with an internal optical loss of as low as 0.34 cm−1. In laser diodes with a cavity length of more than 3 mm, the thermal resistance is reduced to 2°C/W, and the characteristic temperature T0= 10°C is obtained in the range 0–100°C. A record-breaking wallplug efficiency of 74% and an output optical power of 16 W are reached in CW mode. Mean-time-between-failures testing for 1000 h at 65°C with an operation power of 3–4 W results in the power decreasing by 3–7%.

Spontaneously assembling periodic composition-modulated InGaAsP structures

InGaAsP epitaxial layers, which are obtained in the instability region on InP (001) and GaAs (001) substrates, are investigated by photoluminescence and transmission-electronmicroscopy methods. The results are discussed on the basis of the theory of spinodal decomposition of solid solutions. It is established experimentally that in certain temperature and composition ranges the solid solutions InGaAsP are a system of charged, alternating (in mutually perpendicular directions [100] and [010]) domains of a solid solution with two different compositions and different lattice constants. The domain structure is very clearly defined at the surface of the epitaxial film and becomes blurred in the film near the substrate. The data obtained very likely show spinodal decomposition of the solid solutions InGaAsP in the test samples.

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.

High-power laser diodes of wavelength 808 nm based on various types of asymmetric heterostructures with an ultrawide waveguide

The parameters of high-power multimode laser diodes featuring a radiation wavelength of 808 nm obtained on the basis of asymmetric heterostructures with an ultrawide waveguide in the systems of AlGaAs/GaAs and (Al)GaInP/GaInAsP/GaAs are compared. In the lasers based on an AlGaAs/GaAs system, the maximum optical power was limited by optical degradation of the SiO2/Si mirrors and amounted to 4.7 W. In the lasers based on an (Al)GaInP/GaInAsP/GaAs system, the maximum optical power was limited by thermal saturation and equaled 7 W. The obtained results show that the (Al)GaInP/GaInAsP/GaAs system is more reliable from the standpoint of an increase in both the maximum optical power and operation life of lasers.

Epitaxial deposition of InGaAsP solid solutions in the miscibility gap

Liquid-phase epitaxy of InGaAsP solid solutions isoperiodic with (001)GaAs substrates was studied in the miscibility gap. At the initial stage of deposition (first 1–2 s), thin (up to 0.15 µm) planar layers of homogeneous InGaAsP solid solutions are formed. This is aided by pronounced supercooling of the melt (by 10–15°C) and the resulting high growth rates. In further stages, growth becomes slower and a natural nanoheterostructure starts to form owing to decomposition of the solid solution. The formation of a nanoheterostructure comprising domains of different compositions with different lattice constants is accompanied by the appearance of an undulating relief on the sample surface, with the undulation magnitude increasing as the layer grows. Under the technological conditions employed, the thickness of InGaAsP solid solution layers containing a nanoheterostructure is limited to 0.5 µm.

High-power laser diodes with an emission wavelength of 835 nm on the basis of various types of heterostructures

Optical and electrical characteristics of different high-power multimode laser diodes with an emission wavelength of 835 nm are compared; the diodes were obtained on the basis of three systems of solid solutions: AlGaAS/GaAs, AlGaAs/GaAsP, and (Al)GaInP/GaInAsP. An output continuous optical power of 5 W is attained in lasers with a stripe width of 80 μm irrespective of the chosen material system. The highest optical power, 7 W, is attained in the lasers based on the (Al)GaInP/GaInAsP system.

Photoluminescence of heterostructures with highly strained Ga0.76In0.24As quantum wells separated by GaAsyP1-y compensating barriers

Based on the results of model calculations and the data of photoluminescence measurements and transmission electron microscopy, the optimum composition (GaAs0.85P0.15) of compensating barriers for a structure with four highly strained Ga0.76In0.24 As quantum wells (QWs) has been established that excludes the relaxation of elastic stresses in these QWs. Laser heterostructures with four such QWs separated by said compensating barriers have been grown by means of hydride metalorganic chemical vapor deposition. Laser diodes with short (∼100 μm) resonators based on these heterostructures operate at λ = 1060 nm with an output radiation power of 100 mW in the continuous regime.

Self-organizing nanoheterostructures in InGaAsP solid solutions

This paper discusses the photoluminescence and x-ray microstructural properties of epitaxial layers of solid solutions of InGaAsP isoperiodic with InP (100) and GaAs (100) substrates, obtained in the region of immiscibility and spinodal decay. It shows that there is good agreement of the experimental results with the theoretical model of spinodal decay. The boundaries of the region in which two solid phases of different composition exist in epitaxial layers of solid solutions of InGaAsP isoperiodic with the InP and GaAs substrates are determined. A periodic nanoheterostructure is obtained in an epitaxial layer of InGaAsP solid solutions with a repetition period of 650±30 Å in two mutually perpendicular directions.

High-power single-mode laser diodes (λ = 1.1–1.2 μm) based on quantum-confined AlInGaAs/InP heterostructures

Quantum-confined AlInGaAs/InP laser heterostructures emitting at a wavelength of 1.18 μm have been grown by metalorganic vapor-phase epitaxy. An output radiation power of 40 mW in a single-mode CW regime has been obtained using a diode based in this structure with a mesastrip width of W = 4 μm. The total maximum CW emission power amounted to 75 mW.

Photoluminescent and electroluminescent properties of spontaneously forming periodic InGaAsP structures

Photoluminescence and electroluminescence techniques were used to study spontaneously forming periodic InGaAsP structures that consisted of two types of alternating solid-solution domains differing in composition and lattice constant. It was found experimentally that the volume of the narrow-gap material domains is smaller than that of the wide-gap domains. Existence of the inelastic strain caused by the large (2–3%) lattice constant mismatch between the adjacent domains was inferred. Laser diodes with the spontaneously forming periodic InGaAsP structures in the active region were fabricated, and lasing in the long-wavelength electroluminescence spectral band that originated from the radiative recombination in the narrow-gap domains was obtained. Lasing at the threshold current densities of 70 A/cm2 at 77 K and 700 A/cm2 at 300 K was observed in the highest-quality samples.