A. V. Lyutetskiy

850-nm diode lasers based on AlGaAsP/GaAs heterostructures

Laser heterostructures with waveguides and emitter layers made of AlGaAs and AlGaAsP alloys are grown by hydride metal-organic vapor-phase epitaxy on a GaAs substrate and studied. It was shown that the heterostructure containing AlGaAsP layers has a large curvature radius in comparison with the structure consisting of AlGaAs layers. Ridge waveguide lasers with an aperture of 100 μm are fabricated based on the AlGaAsP/GaAs laser heterostructure and studied. The internal optical loss of the lasers is 0.75 cm−1; the characteristic parameter T0 = 140 K in the temperature range of 20–70°C. The maximum optical output power per mirror reached 4.1 W; cw lasing was retained at a heat sink temperature of 120°C.

Temperature delocalization of charge carriers in semiconductor lasers

The temperature dependences of emission characteristics are investigated for laser diodes based on asymmetric separate-confinement heterostructures with a broadened waveguide. It is established that an increase in the charge-carrier concentration in the waveguide layer is the basic mechanism of saturation in the light-current characteristic with increasing temperature in the CW mode. It is experimentally shown that the temperature delocalization of charge carriers leads to increasing internal optical losses and decreasing external differential quantum efficiency. It is shown that the degree of delocalization of charge carriers depends on the charge-carrier temperature distribution, the threshold concentration, and the quantum-well depth. The effect of thickness and energy depth of the quantum well on the temperature sensitivity of the threshold current and output optical power is considered.

A study of epitaxially stacked tunnel-junction semiconductor lasers grown by MOCVD

Design parameters of epitaxially stacked tunnel-junction asymmetric separate-confinement laser heterostructures are chosen. Technological modes for fabrication of heterostructures of this kind by metal-organic chemical vapor deposition in the system of AlGaAs/GaAs/InGaAs solid solutions are found. It is demonstrated that high-efficiency GaAs:Si/GaAs:C tunnel stru ctures and asymmetric AlGaAs/GaAs/InGaAs laser heterostructures with low internal optical loss can be fabricated in a single technological process. Conditions are chosen in which a deep mesa can be formed for fabrication of mesa-stripe diode lasers based on epitaxially stacked tunnel-junction laser heterostructures. Mesa-stripe diode lasers with a 150 × 12-μm aperture have been manufactured on the basis of these structures. These samples have a threshold current density Jth of 96 A cm-2, internal optical loss αi of 0.82 cm-1, and differential resistance R = 280 mΩ. Samples containing three laser structures have a slope efficiency of 3 W A-1 and a maximum peak output power of 250 W in the pulsed operation mode (100 ns, 1 kHz).

Thermal delocalization of carriers in semiconductor lasers (λ = 1010–1070 nm)

The temperature dependences of the emission characteristics of semiconductor lasers based on MOVPE-grown asymmetric separate-confinement heterostructures (wavelengths λ = 1010–1070 nm) have been studied. It was found that, in the continuous-wave mode, the main mechanism of “saturation” of the light-current characteristic with increasing temperature of the active region is carrier delocalization into the waveguide layer. It was experimentally demonstrated that the thermal delocalization of carriers depends on the energy depth of the quantum well (QW) in the active region. It is shown that the minimum internal optical loss at 140°C is obtained in laser structures with the largest energy depth of the QW of the active region.

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.

Acoustoelectron interaction in quantum laser heterostructures

The effect of ultrasonic deformation on the polarization properties of semiconductor quantum-well laser radiation is experimentally and theoretically studied at room temperature. It is shown that the observed rotation of the polarization plane is caused by mixing of the light- and heavy-hole levels in the quantum well. Data on the splitting energy of these levels are obtained. The unique capability of the ultrasonic technique for obtaining data on the value and distribution of technological strains in the heterostructure is shown.

Properties of AlN films deposited by reactive ion-plasma sputtering

The properties of SiO2, Al2O3, and AlN dielectric coatings deposited by reactive ion-plasma sputtering are studied. The refractive indices of the dielectric coatings are determined by optical ellipsometry. It is shown that aluminum nitride is the optimal material for achieving maximum illumination of the output mirror of a semiconductor laser. A crystalline phase with a hexagonal atomic lattice and oxygen content of up to 10 at % is found by transmission electron microscopy in the aluminum-nitride films. It is found that a decrease in the concentration of residual oxygen in the chamber of the reactive ion-plasma sputtering installation makes it possible to eliminate the appearance of vertical pores in the bulk of the aluminum-nitride film.

850-nm diode lasers with different ways of compensating for internal mechanical stresses in an AlGaAs:P/GaAs heterostructure

MOS hydride epitaxy is used to grow AlGaAs/GaAs heterostructures both without compensation and with compensation for internal mechanical stresses by the introduction of phosphorus into different layers of the heterostructure; this compensation affects the lattice parameter of the layer and, thus, influences the value of internal stresses in the entire laser hetetrostructure. Multimode mesastripe laser diodes (with an aperture of 100 μm) emitting at a wavelength of 850 nm are fabricated on the basis of the above structures; the properties of these diodes are studied. It is shown that the structures with compensated internal mechanical stresses exhibit a linear power-current characteristic if the pump currents do not exceed those corresponding to the maximum of the output power. Such structures with compensated internal mechanical stresses exhibit larger values for the characteristic temperatures T0 and T1 in comparison with structures with uncompensated internal mechanical stresses.

Temperature dependence of the threshold current density in semiconductor lasers (λ = 1050–1070 nm)

The temperature dependences of the threshold current density and threshold concentration in semiconductor lasers based on MOVPE-grown asymmetric separate-confinement heterostructures with an extended waveguide have been studied (wavelengths λ = 1050–1070). It is shown that the temperature dependence of the threshold current density in semiconductor lasers becomes markedly stronger at above-room temperatures, which is due to temperature-induced carrier delocalization into the waveguide layers of a laser heterostructure. It was found that the sharp decrease in the thermal stability of the threshold current density with increasing temperature correlates with the coincidence of the Fermi level with the conduction-band bottom of the waveguide layer in the laser heterostructure. It is experimentally demonstrated that an increase in the energy depth and number of quantum wells in the active region of a semiconductor laser improves the thermal stability of the threshold current density. It is demonstrated that the characteristic parameter T0 attains a value of 220 K in the temperature range from −20 to +70°C.

Quenching of lasing in high power semiconductor laser

Emission characteristics of high-power semiconductor lasers with a mesa-stripe design based on heterostructures with separate confinement are studied. It is shown that, in high-power semiconductor lasers with a mesa-stripe design, divergence of emission increases with the pump current as a result of generation of high order lateral optical modes. It is demonstrated that scattered radiation of high order lateral optical modes affects the transparency of passive regions outside the mesa stripe that forms a waveguide of the Fabry-Perot resonator. It is established that the transparency of passive regions results in fulfillment of threshold conditions for the closed optical mode in the semiconductor laser’s chip. As a result of generation of the closed optical mode in a cavity formed by four cleaved faces quenching of lasing modes in the mesa-stripe waveguide of the Fabry-Perot resonator occurs.