Patterning Of Sapphire Substrates For GaN Epitaxy

Patterned sapphire substrates can reduce the dislocation density of GaN crystal,improve internal quantum efficiency of LED,and improve light-emitting efficiency of LED,which has attracted extensive attention at home and abroad in recent years.In this paper,nano-scale patterned sapphire substrats were prepared by combining wet etch-ing and nanocolloidal spheres etching.The quality of colloidal spheres mask,SiO₂ mask,nano-patterned sapphire substrates and GaN were characterized by SEM,AFM,XRD and other characterization methods.Optimal preparation process was obtained by optimizing the process parameters,which provided a reference for the preparation of nano-patterned sapphire substrates in the future.PS colloidal sphere masks were prepared by spin-coating method,liquid dropping method and gas-liquid interface self-assembly method respectively.The effects of different methods on the preparation of PS colloidal sphere masks were studied.The results showed that the colloidal sphere masks prepared by spin-coating method were closel yarranged in the center of substrate,but there was a stacking phenomenon at the edge of the substrate.The dense and ordered mask structure could not be obtained by ti-tration.The colloidal sphere masks prepared by gas-liquid interface self-assemblymethod were uniform,compact and defect-free.Therefore,a colloidal sphere masks were prepared by a gas-liquid interface self-assembly method.The process conditions of etching colloid spheres by ICP technology were optimized.The effects of etching power,O₂ flow rate and etching time on the diameter of colloid spheres were studied by analyzing the mechanism of etching colloid spheres by ICP technology.The opti-mal etching process was 230W,20sccm and 20s.The preparation conditions of SiO₂thin films on sapphire substrates were optimized.The effects of different sputtering powers and pressures on the preparation of SiO₂ thin films were studied by analyzing the mechanism of magnetron sputtering.The optimum sputtering conditions were100W and 1.2Pa.The process conditions of etching SiO₂ thin films by ICP technology were optimized.Through the mechanism analysis of etching SiO₂ thin films by ICP,the effects of different etching power,O₂ flow rate and etching time on the etching of SiO₂ thin films were studied.The optimal etching process of SiO₂ thin films were360W,10sccm and 7min.Nano-patterned sapphire substrates were prepared by wet etching using SiO₂ nanorod as mask and GaN was epitaxially grown.The effects of different ratios of acid solution,wet etching products,etching temperature and etching time on sapphire etching were studied.The quality of GaN epitaxially grown on a flat sapphire substrate and a nano-scale patterned sapphire substrate was compared.The results showed that when the volume ratio of concentrate sulfuric acid to concentrated phosphoric acid was 3:1,the etching rate of sapphire was the fastest.It was found that Al₂?SO₄?₃·17H₂O,a product of wet etching,adhered to the surface of the sapphire substrate and hindered the etching of the sapphire substrate.Under the same etching time,the etching solution temperature increased and the etching rate of sapphire substrate increased.At the same etching temperature,the etching time increased and the patternsize decreased further.Compared with GaN grown on a flat sapphire subs-trate,the quality of GaN grown on a nanoscale patterned sapphire substrate was improved.