Research On Corrosion And Re-Growth Of AlGaN Materials

In recent years,group Ⅲ nitrides LED by GaN have been widely used in the preparation of high-performance and low-cost LED optoelectronic devices due to their direct bandgap,large forbidden band width and high electron mobility.Among them,AlGaN-based ultraviolet LEDs have gradually become The focus of GaN-based LED development research.The main problem facing AlGaN-based LEDs is the low internal quantum efficiency and low luminous efficiency.The main reason is that AlGaN materials are limited by the lack of suitable homoepitaxial substrates,and more use heteroepitaxial growth,which will lead to a large number of dislocations and defects are generated,thereby reducing the internal quantum efficiency.Therefore,this paper is based on the idea of defect-first etching,through solution chemical corrosion,electrochemical corrosion and melt chemical corrosion three kinds of corrosion methods,samples with different types of corrosion pits are obtained.The characterization and analysis of the samples after the second epitaxy were carried out,and the mechanism of different corrosion methods and different types of corrosion pits in the improvement of material quality was compared.First,the prepared n-AlGaN sample is etched first.In order to compare the corrosion effects of different corrosion methods on the sample surface,and to explore the best process of different corrosion methods,this paper designs three sets of corrosion for three corrosion methods.The test and research can get:(1)In the solution corrosion experiment,50ωt% KOH solution is used for corrosion,and the size,depth and density of the corrosion pits are positively correlated with the corrosion temperature and corrosion time.Comparative analysis shows that the optimal corrosion conditions are: the corrosion temperature is 40℃ for 10 min.The average diameter of the corrosion pits is 160 nm and the average depth is 8 nm.They are inverted hexagonal prisms,which correspond to the screw dislocations in the sample.(2)In the electrochemical corrosion experiment,a DC voltage source was used to corrode in a 5ωt%KOH solution.The study found that the size,depth and density of the corrosion pits are positively correlated with the corrosion time and corrosion voltage.Among them,when the corrosion voltage is constant,As the corrosion time increases,the corrosion tends to proceed longitudinally,and at the same time,fine small corrosion pits appear on the surface of the electrochemically corroded sample.Comparative analysis shows that the optimal corrosion condition is that the corrosion pits are corroded at 30 V for 5 min with an average diameter of 230 nm and an average depth of35 nm.They are inverted hexagonal prisms and inverted hexagonal pyramids,corresponding to each screw dislocations and edge dislocations.(3)In the molten corrosion test,the sample was corroded by molten KOH.The depth of the corrosion pit on the sample surface was between 50 nm and 500 nm,and the diameter was between 1 μm and1.3 μm.At the same time,the sample surface was seriously damaged,and there were three corrosion pits.The types are inverted hexagonal prism type,inverted hexagonal pyramid type and the combination of the two types,respectively corresponding to screw dislocations,edge dislocations and mixed dislocations.In order to study the material improvement effect of defect priority corrosion,the samples after electrochemical corrosion and solution chemical corrosion were subsequently subjected to secondary epitaxy.The surface of the sample treated by different corrosion methods will expose corrosion pits corresponding to different types of dislocations.During the secondary epitaxial growth,the dislocations will bend and merge at the corrosion pits and eventually disappear.The analysis of different samples after the secondary epitaxy shows that the chemical corrosion regrowth of solution KOH has a good inhibitory effect on screw dislocations,and the electrochemical corrosion regrowth has a good inhibitory effect on screw dislocations and edge dislocations.At the same time,the sample after corrosion treatment will release the tensile stress during the growth process to a certain extent due to the existence of corrosion pits after the second external delay.The effect of electrochemical corrosion on stress improvement is better than solution chemical corrosion;Finally,based on defect priority corrosion,the SiNx mask layer method is used to further analyze the growth of AlGaN material during the secondary epitaxy process.The experiment shows that SiNx will be preferentially covered by dislocations,and more window layers will be exposed at the same time.The leaked window will grow homogeneously during the second epitaxy,forming more and larger nucleation sites,and merge with lateral epitaxial growth in the subsequent growth.In this paper,the optimal corrosion conditions are found by optimizing the experimental parameters,and the secondary epitaxy after defect priority etching improves the quality of regrown samples,and electrochemical corrosion has a better dislocation suppression effect than solution chemical corrosion.It is concluded that the use of the SiNx mask layer on the etch pit has a better dislocation suppression effect than the traditional SiNx mask layer method.