Study on Quantum Well Intermixing Induced by Zn Impurities in GaInP/AlGaInP Red Semiconductor Lasers
As the photovoltaic conversion efficiency and output power of high-power lasers continually ascend,the escalating impact of Catastrophic Optical Damage(COD)effects occurring at the laser cavity surface poses an increasingly severe challenge.Consequently,a post-processing technique involving Quantum Well Intermixing(QWI)can be employed at the cavity surface to fabricate a Non-absorption Window(NAW),thereby augmenting the COD threshold and amplifying the output power.Given the swift diffusion of Zn in GaAs-based semiconductor lasers,Zn impurity-induced QWI is favorably regarded.In the epitaxial growth of GaAs-based GaInP/AlGaInP single quantum well structures,ZnO thin films were selectively grown on the epitaxial wafer using magnetron sputtering equipment.Utilizing ZnO as the medium for Zn impurity induction,a solid-state Zn diffusion process was employed to selectively induce regions in the laser,thereby increasing the bandwidth at the laser cavity surface to prepare NAW and elevate the threshold for optical damage,consequently enhancing the long-term reliability and output power of the semiconductor laser.In addition to the induction annealing experiments conducted with a single ZnO dielectric layer,experiments were also conducted with composite dielectric layers ZnO/Si3N4 and ZnO/SiO2.These experiments involved the growth of these composite layers using Plasma Enhanced Chemical Vapor Deposition(PECVD)equipment atop the ZnO dielectric layer.Initially,through simulation calculations,it is observed that for p-type doping such as Mg impurity,as the doping concentration increases,Zn diffusion in GaAs or InP accelerates,resulting in deeper diffusion depths under the same time conditions.Conversely,for n-type doping such as Si,an increase in doping concentration impedes Zn diffusion.Moreover,the diffusion of Zn in GaAs-based epitaxial wafers surpasses that in InP-based wafers.During the diffusion process,the composite dielectric layers ZnO/Si3N4 and ZnO/SiO2 can alter the type of stress exerted by the singular ZnO dielectric layer.This shift transforms from the tensile stress applied by the ZnO single dielectric layer to the compressive stress exerted by the composite dielectric layer.The compressive stress has the potential to induce more Ga vacancies on the epitaxial wafer surface,thereby facilitating Zn diffusion within the laser epitaxial layers.Defect formation energies of Zn in AlGaAs and GaInP were also calculated,indicating the propensity of Zn to occupy Group III atoms such as Al and Ga.This supplementation contributes to a comprehensive understanding of the induction principles governing QWI.Experimental investigations,conducted under annealing conditions ranging from 580℃ to 680℃ for 20 min to 60 min,revealed that the adoption of ZnO/SiO2 or ZnO/Si3N4 composite dielectric layers yielded a greater impurity-induced blue shift compared to a single Zn dielectric layer,with a maximum blue shift of 55 nm achieved under conditions of 680℃ for 30 min.Additionally,a study was undertaken on the long-term,low-temperature effects of composite dielectric layer ZnO/SiO2 annealing on solid-state Zn diffusion,with temperatures set at 520℃,550℃,and 580℃,and times specified at 9 h.Blue shifts were observed at 0.9 nm,1.4 nm,and 24.8 nm,suggesting the pivotal role of temperature in QWI even under prolonged low-temperature annealing conditions.Through experimental endeavors and analysis,it is established that NAW can be successfully fabricated under prolonged low-temperature annealing conditions exceeding 580℃ for 9 h or under relatively higher-temperature,short-duration conditions at 650℃ for 30 min.To minimize the impact of high-temperature annealing on the performance and quality of the epitaxial wafer,a cyclic annealing approach was adopted,employing annealing cycles at 620℃ for 30 min.The annealing process was repeated three times.Following 1 to 3 cycles of annealing,the observed blue shifts were 10 nm,18.1 nm,and 35.6 nm,respectively.After three cycles,an optimal blue shift window of approximately 30 nm was achieved.This study furnishes theoretical and experimental references for device fabrication.Not only does this research offer essential information for optimizing the performance and fabrication of semiconductor lasers,but it also expands our understanding of the operational mechanisms of composite dielectric layers in the context of QWI.
Semiconductor laserQuantum well intermixingComposite dielectric layerBlue shiftNon-absorption window
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