Investigate Epitaxial Growth Of High Quality GaN Films On Si Substrate By MOCVD

GaN materials have wide band gaps,high melting points,high electron mobility,high breakdown field strength,and high thermal conductivity.They are widely used in light emitting devices?LEDs?,solar cells,high electron mobility transistors,and RF devices.At present,the epitaxial GaN films are basically heteroepitaxially grown by the MOCVD method.Generally,heteroepitaxial substrates for commercial use are sapphire and Si C.Compared with the above two substrates,epitaxial GaN thin films devices using Si substrates have the advantages of low cost,large size,and good thermal conductivity.However,there are also some problems with epitaxial GaN films on Si substrates.For example,large lattice mismatches cause defects,and large thermal expansion coefficient mismatches cause cracks on the GaN films surface,and Si and Ga are prone to chemical reactions to form alloy etching substrates and the entire epitaxial layer.This article systematically analyzes and discusses the growth process of MOCVD epitaxial GaN films on Si substrates.The main research contents are as follows:?1?The optimal preflow of TMAl of pre-Al is studied.The results show that the flow rate of TMAl in pre-Al is 59.5 sccm,which can prevent the formation of amorphous Si_xN_y and the phenomenon of back-melting etching on GaN films surface.?2?The effect of growth conditions of AlN buffer layer for GaN epitaxial layer was studied.The results show that the best quality of GaN films is obtained at AlN buffer layer with growth pressure of 50 mbar,temperature of 1100°C and growth thickness of 160 nm.?3?Epitaxially grown films on LT/HT?AlN double buffer layer,The results show that when the temperature of the LT?AlN layer is 1000?and the thickness is 20 nm,cracks on the surface of the GaN thin films can be reduced to a certain extent,and the crystalline quality of the GaN epitaxial layer can be improved.?4?The stepped Al_xGa_1-xN stress relaxation layer was used.The results show that the intercalation layer can improve the crystal quality of GaN,reduce the crack of GaN epitaxial layer,and improve the surface morphology of GaN layer.We optimized the Al composition inserted into the Al_xGa_1-xN layer and obtained the optimal low Al composition step growth structure.