Effect of the active region thickness on characteristics of semiconductor lasers based on asymmetric AlGaAs/GaAs/InGaAs heterostructures with broadened waveguide

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 In_xGa_1–x As layer in the active region is exceeded.     

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 J _th of 96 A cm^-2, internal optical loss α_i 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).     

On the temperature delocalization of carriers in GaAs/AlGaAs/InGaAs quantum-well heterostructures

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.     

On the problem of internal optical loss and current leakage in laser heterostructures based on AlGaInAs/InP solid solutions

Semiconductor lasers based on MOCVD-grown AlGaInAs/InP separate-confinement heterostructures are studied. It is shown that raising only the energy-gap width of AlGaInAs-waveguides without the introduction of additional barriers results in more pronounced current leakage into the cladding layers. It is found that the introduction of additional barrier layers at the waveguide–cladding-layer interface blocks current leakage into the cladding layers, but results in an increase in the internal optical loss with increasing pump current. It is experimentally demonstrated that the introduction of blocking layers makes it possible to obtain maximum values of the internal quantum efficiency of stimulated emission (92%) and continuouswave output optical power (3.2 W) in semiconductor lasers in the eye-safe wavelength range (1400–1600 nm).     

Pulsed semiconductor lasers with higher optical strength of cavity output mirrors

Asymmetric heterostructures with an ultrathick waveguide based on an AlGaAs/GaAs alloy system that allow lasing at a wavelength of 905 nm have been developed and fabricated by hydride metalorganic vapor-phase epitaxy. The internal optical loss and internal quantum efficiency of semiconductor lasers based on such structures were 0.7 cm^-1 and 97%, respectively. It is shown that the highest output optical power of laser diodes with antireflecting (SiO₂) and reflecting (Si/SiO₂) coatings deposited on untreated Fabry-Perot cavity facets obtained by cleaving in an oxygen atmosphere reached 67 W in the pulsed mode and is limited by mirror damage. Treatment of Fabry-Perot cavity facets by etching in argon plasma and the formation of coatings with passivating and oxygen-blocking GaN and Si₃N₄ layers allowed an increase in the maximum output optical power to 120 W. Mirror damage was not observed at the attained output optical power.     

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

Semiconductors - 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...     

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.     

Dependence of the electron capture velocity on the quantum-well depth in semiconductor lasers

Three laser structures with a single strained InGaAs quantum well of different depths and a GaAs or Al_0.1Ga_0.9As waveguide region are grown by metal-organic chemical vapor deposition. Using the experimentally determined values of the threshold current density and internal differential quantum efficiency, the velocity of electron capture into the quantum well is calculated for each of these structures. It is found that the capture velocity into deep quantum wells is significantly lower than into shallow ones.     

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 ?? = 1010?C1070 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.