Self-organized Growth Of GaN Micro And Nanorods

Compared with traditional epitaxial film materials,gallium nitride(GaN)micro and nanomaterials have the characteristics of larger surface-to-volume ratios,lower dislocation density and independent distribution growth.Those have important significance in the preparation of high efficiency,long life and flexible GaN-based photovoltaic devices.In the process of preparing GaN micro and nanorods,mask etching,metal droplet catalysis and selective epitaxy need to additional introduce systems,which will adversely affect the GaN crystal quality and performance.In order to avoid interference from external factors,it is necessary to realize the self-organized growth of GaN micro and nanorods.In this thesis,the self-organized growth process of GaN microrods and nanorods was studied by metal organic chemical vapor deposition and halide chemical vapor deposition.First,the exfoliated multilayer graphene was etched in situ by metal organic chemical vapor deposition,and GaN microrods were grown on the graphene by a two-step method.The effect of ammonia(NH₃)/hydrogen(H₂)flow ratio on the growth density of GaN seed crystals on graphene,the effect of growth time on the growth morphology of GaN seed crystals,and the effect of growth temperature,reaction pressure,silane flow rate,V/III ratio,growth time on the morphology of GaN microrods were studied.Secondly,in the home-made halide chemical vapor deposition,the growth of GaN nanorods was achieved using gallium trichloride as precursor.The effects of NH₃flow rate,growth temperature and gradient temperature growth process(800-900?)on the morphology,quality and luminescence properties of GaN nanorods were studied.The specific research results are as follows:(1)In order to grow larger microrods on multi-layer graphene,the graphene is etched in-situ by metal organic chemical vapor deposition device to prepare micro defects and dangling bonds for epitaxial growth,and then GaN seeds are grown in the middle temperature stage to provide growth sites for GaN microrods.Scanning electron microscope results show that the etching effect on graphene becomes more and more obvious with the increase of NH₃ flow rate under high temperature etching conditions.When NH₃/H₂ reaches 0.9,dense GaN seeds can be grown on the multilayer graphene.And GaN seeds undergo a pregnant period before reaching a stable state.With time extended to 60 s,GaN seeds reach a fixed crystal size and appear smooth crystal planes,which has an important effect on the growth morphology of GaN microrods.In the subsequent growth of GaN microrods,it is found that higher growth temperature,higher reaction pressure,and higher silane flow rate will promote the growth of GaN microrods in the axial direction and inhibit their growth in the radial direction,the smaller V/III ratio can avoid the merger caused by the higher lateral growth rate,which is conducive to the formation of micrometer rods with a large ratio of length and diameter.When the growth time is extended,the growth density of GaN microrods decreases and the axial growth rate increases.(2)To explore the process of GaN nanorods grown from gallium trichloride,a home-made multi-tube halide chemical vapor deposition system is used for regulating.Scanning electron microscope results show that NH₃ flux and growth temperature have a significant effect on the morphology of GaN nanorods.With the increase of NH₃flux,GaN nanomaterials tend to grow laterally and merge to form a rough thin film.The morphology of GaN nanorods is different at various temperature.At 900?and 60 sccm of NH₃ flow,nanorods with a hexagonal structure can be grown,and the X-ray diffraction results show that the GaN crystal is of good quality.In the photoluminescence spectrum,there is a clear near-band edge luminescence peak at 366 nm,and there is no obvious red defect peak at 680nm.After the gradient temperature(800-900?)growth process,the scanning electron microscope results show that the density of GaN nanorods decreases,the size along the axial direction becomes larger,the growth morphology becomes complicated,surface-to-volume ratios increases,and in the photoluminescence spectrum,the intensity of near-band edge luminescence peak is greatly improved.