Study On The Fabrication Of High In Component AlInN Materials And Its Photoelectric Properties

By varing the In composition,the band gap of Al_1-xIn_xN can be continuously adjusted in the range of 0.7-6.2e V.It is widely used in distributed Bragg reflector,micro-cavity,superlattice Al In N/Ga N quantum well,UV light-emitting LED,solar cell,high frequency millimeter-wave device and high voltage power switching device.In general,Al_1-xIn_xN is prepared by MOCVD.The reaction source is organic compounds.The temperature is usually around 1000℃.As the high In component Al_1-xIn_xN is prepared at this temperature,the In-N bond is prone to fracture due to high energy,and the Al-N bond is relatively stable.That results in the overall phenomenon of uneven composition,phase separation and In segregation.Furthermore,it will result in poor roughness and increased crystal structure defects in the film.Facing this problem,the In and Al metals are used as reaction sources.By lowering the preparation temperature,the fabrication of high In component Al_1-xIn_xN materials and its photoelectric properties are researched in this paper.The specific research progress is as follows:In N nanowires,nanoribbons,nanotubes and nanosheets are fabricated by CVD technology around 700℃,which are adjusted by the concentration of In and N molecules.Based on the SEM,XRD,TEM,Raman and photoluminescence characterization of the nanostructure,a reasonable model is established to discuss the morphologic evolution mechanism of In N nanowires to nanotubes and nanoribbons.The results show that In N nanowires can grow into serrated nanosheets in the form of nanoleaf film,and then form large nanosheets,long nanoribbons and hollow nanotubes.The PL spectra of In N nanowires can be blue shifted by the morphologies of these nanostructures,with a maximum of0.208e V.The crystal structure and growth mechanism of single-crystal non-polar In N nanosheets synthesized by two-step controlled CVD method are studied.The results show that using the M-plane of Ga N nanowires as template can inhibit the the radial growth rate of In N nanocrystals,reduce the axial growth rate,so that In N nanocrystals can be heteroepitaxial growth to non-polar nanosheets at high In molecular concentration.Al_1-xIn_xN thin film is prepared on Si（100）substrate at 200℃by magnetron sputtering using independent high purity Al In（99.999%）target as Al source and In source.The study of gas flow rate,sputtering pressure and sputtering time on the preparation of Al_1-xIn_xN thin films is improved.By increasing the N₂ gas ratio,the atomic percentages of In and Al in the films increase.The percentage of In is greater than that of Al,which demonstrates the formation of In-rich Al_1-xIn_xN film.The increase of the reactor pressure can lead to the collision probability of gas molecules with sputtering atoms increases with the volume molecules.The In-Al-N atoms deposited on the surface of the film migrate and recombine in a low energy state to agglomerate particles,which induce the increscent grain size and poor crystallinity.This expands the thermal stress of the film and promotes the island growth of the films.The sputtering metal particles increase with the extension of the sputtering time,leading to the formation of polycrystalline structures in Al_1-xIn_xN films.The optimized process parameters are as follows:Ar gas flow rate is 6sccm,N₂ gas flow rate is 18sccm,sputtering pressure is 1Pa and sputtering time is 60min.The In component（X）of high In component Al_1-xIn_xN films is 0.6 by XPS analysis,1.97 e V by energy band gap calculation,and 1076（Ω/□）by square resistance calculation.The photoelectric properties of high In component Al_1-xIn_xN thin films prepared on Si（100）and sapphire substrates are studied.The optoelectronic devices are fabricated on Si（100）substrate.The significant photoelectric response behaviors are observed.The saturation time of photocurrent is 0.8～1.0s.In the range of 350～700 nm,the maximum response rate of the photodetector is 0.08 A/W at 580 nm.The I-V characteristics of optoelectronic devices are studied in dark field and light condition.At 10 V bias,the dark current and photocurrent are 6.78×10^-8A and 1.11×10^-7A,respectively.The photoelectric response of the device prepared at 100,300 and 350℃are studied.The device performance can be degraded by the variation of surface structures in Al_1-xIn_xN films,which influenced by the temperature.An improved vertical structure photodetector is designed and fabricated on sapphire substrate,and the reasons for its improved performance are analyzed in three cases.When the bias voltage is 10 V,the optoelectronic device can produce a stable photocurrent of about 0.2m A.The effects of gas flow rate,sputtering pressure and sputtering time on the growth mechanism is a great significance for the research of high In component Al_1-xIn_xN films.Based on the photoelectric characteristics of Al_1-xIn_xN films on Si（100）and sapphire substrates,the further development of corresponding optoelectronic devices can be promoted.