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The emission characteristics of narrow mesa-stripe (5.5 μm) lasers based on asymmetric AlGaAs/GaAs heterostructures are studied. It is shown that the maximum optical power achieved in the continuous-wave (CW) operation mode is limited by heating and reaches a value of 1695 mW at a current of 2350 mA at +25°C, with the maximum efficiency reaching 54.8%. Reducing the working temperature to –8°C makes it possible to raise the maximum low-mode CW power to 2 W. A peak power of 2930 mW is obtained under pumping with current pulses (width 240 ns, amplitude 4230 mA). It is shown that the power profile has in the pulsed mode an "optical dip" region in which low-efficiency lasing occurs with the generation of a train of subnanosecond pulses. [ABSTRACT FROM AUTHOR]

The effect of temperature delocalization in semiconductor lasers (emission wavelength λ = 1060 nm) based on symmetric and asymmetric separate-confinement heterostructures fabricated by metal-organic vapor-phase epitaxy (MOVPE) is studied. Experimental and calculated estimates show that the carrier concentration in the waveguide increases by an order of magnitude when the temperature of a semiconductor laser is raised by ∼100°C. It is found that an increase in the temperature of the active zone leads to enhancement of the temperature delocalization of both electrons and holes. It is shown that the delocalization of holes begins at higher temperatures, compared with that of electrons. It is demonstrated experimentally that the onset of temperature delocalization depends on the threshold carrier concentration in the active region of a laser at room temperature. It is found that raising the energy depth of the active region by choosing the waveguide material makes it possible to fully suppress the temperature-delocalization process up to 175°C. [ABSTRACT FROM AUTHOR]

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 T and T in comparison with structures with uncompensated internal mechanical stresses. [ABSTRACT FROM AUTHOR]

Laser diodes with a deep built-in trapezoidal large-period diffraction grating have been developed on the basis of InGaAs/GaAs/AlGaAs heterostructures. The electroluminescence and stimulated emission spectra and light-current characteristics of diffraction-grating laser diodes have been studied. A substantial narrowing of both the luminescence and stimulated emission spectra was achieved due to the spectral selectivity of the grating. The maximum output optical power was 1 W at a drive current of 4 A. At the highest power, the lasing spectrum had a FWHM of ∼2 Å. A narrowing of the lasing spectrum of the diffraction-grating laser by tens of times was demonstrated, compared with that of a laser with a Fabry-Perot cavity. [ABSTRACT FROM AUTHOR]

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 T attains a value of 220 K in the temperature range from −20 to +70°C. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The effect of the active region thickness on the basic characteristics of high-power semiconductor lasers based on AlGaAs/GaAs/InGaAs asymmetric separate-confinement heterostructures grown by MOCVD epitaxy has been studied. It is shown that the threshold current, temperature sensitivity of the threshold current density, internal quantum efficiency of stimulated emission, and differential quantum efficiency are improved as the active region thickness increases. It is demonstrated that the maximum attainable optical emission power of a semiconductor laser and the internal quantum efficiency of photoluminescence are the most sensitive to defect formation in the heterostructure and become lower as the critical thickness of the strained InxGa1–x As layer in the active region is exceeded. [ABSTRACT FROM AUTHOR]

Asymmetric Al0.3Ga0.7As/GaAs/InGaAs heterostructures with a broadened waveguide produced by the method of MOCVD epitaxy are studied. It is established that the precision shift of the active region to one of the cladding layers ensures the generation of the chosen mode of high order in the transverse broadened waveguide. It is experimentally established that this shift brings about an increase in internal optical losses and a decrease in the internal quantum efficiency of stimulated emission. It is shown experimentally that the shift of the active region to the n-type cladding layer governs the sublinear form of the power-current characteristic for semiconductor lasers; in the case of a shift of the active region towards the p-type cladding layer, the laser diodes demonstrated a linear dependence of optical power on the pump current in the entire range of pump currents. [ABSTRACT FROM AUTHOR]

Spectral and emission-power characteristics of semiconductor lasers based on quantum-dimensional asymmetric heterostructures with separate confinement in a system of InGaAs/GaAs/AlGaAs alloys are studied in the case of high pump levels in the pulsed mode of lasing (200 A, 100 ns, and 10 kHz). It is shown that, in lasers with a quantum-dimensional active region containing one or two levels of dimensional quantization, the spectrum consists of one or two lasing bands. It is established that the condition for inverse population of the second electron level and two-band lasing are attained due to leveling-off of the rate of stimulated recombination from the first electron level and a high density of states for the second level. It is shown that, in lasers with double-band lasing spectrum, the total emission spectrum exceeds appreciably the emission power of a laser with a single electron level and a single spectral band. [ABSTRACT FROM AUTHOR]

High-power semiconductor lasers based on asymmetric quantum-dimensional separate confinement InGaAs/GaAs heterostructures with ultrathick waveguides were fabricated by means of metalorganic hydride vapor phase epitaxy technology. The laser characteristics were studied in a pulsed pumping regime, in which the emission was excited by current pulses of 100 ns duration at a repetition frequency of 10 kHz and an amplitude of up to 200 A. The passage to a pulsed lasing regime allowed the active region heating to be reduced and the output power to be increased to 145 W for a laser diode with a 100-μm exit aperture. The results obtained for the pulsed lasing regime show that saturation of the output power-current characteristic observed in the continuous-wave regime is fully determined by overheating of the active region of a semiconductor laser. [ABSTRACT FROM AUTHOR]

InGaAsP/InP laser heterostructures with step-divergent waveguides and two stressed quantum wells were obtained by metalorganic VPE. The lasers emitting at 1.55 µm provide for an intrinsic quantum yield of η[sub i] = 85 %. An optical power of 5.2 W in the continuous operation mode was achieved at a laser diode temperature of 10°C. The internal optical losses in the laser heterostructure studied amount to 3.6 cm[sup -1], which is comparable with the level of losses in similar structures with uniform divergent waveguides. [ABSTRACT FROM AUTHOR]