Study On Degradation Mechanism Of Epitaxial Layer Structure Of AlGaInAs Near Infrared Semiconductor Lasers

The AlGaInAs material system is an indispensable material as the active layer of semiconductor diode lasers emitting wavelength at 1310 nm or 1550 nm owing to the incomparable characteristics such as low threshold current density,high modulation speed and external quantum efficiency.The use of semiconductor laser diodes with emitting wavelengths at 1310 nm or 1550 nm has become more widespread in optic-fiber communications and fiber optic sensor,etc.Recent years,as the continuous improvement of output power characteristics in semiconductor lasers,the market of their applications is constantly expanding.However,the reliability of diode lasers is still one of the most important factors limiting its application.Especially for the quaternary systems with relatively complicated crystal structures,which have more complex defects than binary and ternary material systems.Besides,since the performance characteristics of the quaternary long-wavelength lasers are usually quite sensitive to environmental temperature,the degradation processes in these devices are very significant at high temperature.Therefore,it is still a very important research topic to deeply and comprehensively study the failure mechanism of AlGaInAs QW diode lasers.After a long working time,the effects of current/voltage overload,current surge,thermal overload,etc will occur in semiconductor diode lasers.The thermal effects would induce heat accumulation in optical devices.Local temperature of the active region is exorbitant,leading to the formation of defects.The density of defect reaches a certain degree,the performance characteristics and lifetime of devices would be influenced,resulting in the degradation or even failure of devices.In this paper,the epitaxial layers of near-infrared strained Al_0.07Ga_0.22In_0.71As QW semiconductor diode lasers are studied as object of research.These epitaxial layers were heat treated at 170?so as to accelerate the aging of properties.Heat treatment was adopted to simulate the degradation processes in the active region of diode lasers after working for a long time.The effects of heat treatment duration on the changes in the structural and optical properties of AlGaInAs QW epitaxial wafers were studied.The variation of component and its'diffusion process in the active region caused by temperature were also characterized.In addition,the defects evolution led by composition fluctuations were analyzed.Thus,the degradation mechanism is explored.The main experimental results are as follows:1.The microstructure changes and evolution of strained AlGaInAs QW layers induced by heat treatment were studied by means of spatially resolved cathodoluminescence?SRCL?.It is found that the SRCL distribution of strained AlGaInAs QW annealed after 4 hours was obviously discretized.The segregation of Indium atoms was determined.The PL decay exhibited a characteristic decay time that was 20 times shorter than the sample as grown.The obvious increasing of the dark spots'density?defect core region?,significant alloys fluctuations,the dramatic segregation of Indium atoms between inter-layers and the degradation of lattice quality in AlGaInAs QW layers after longer annealing times are probably the dominant factors of faster PL decay.2.The defect area was clearly observed in the AlGaInAs QW layer after thermal treatment.CL emissions from the defect core have higher emission energy than those from the defect-free regions,thus indicating the defects contained less indium atoms than the surrounding matrix.The indium atom diffusion process was asymmetric near the defect region.It is implied that a weak diffusion of the indium atoms intra-layer,and a dominant diffusion between inter-layers a after long annealing time.3.At ultra-low temperature,an abnormal S-shaped curve in PL emission peak energy and a non-monotone evolution in spectral band width which is opposite to the traditional variation model were observed in strained AlGaInAs QWs with different heat treatment durations.A highly linear correlation between full width at half maximum?FWHM?and emission energy with temperature was exhibited in samples with different heat-treatment durations.The highly linear correlation demonstrated that the dependencies and relationships between PL peak energy and FWHM vs temperature are consistent.The mechanism dominated their evolutions with temperature is:the anomalous blue shift and concomitant narrowing of FWHM were attributed to lattice strain fluctuations due to difference of thermal expansion coefficient between adjacent layers and strong carriers'localization.4.The thermal energy for photon-generated carriers moving from the band edge to localization centers was independent of annealing durations.