AlGaN Fabrication Based On Nano-patterned Template And Research Of AlGaN Ultraviolet Avalanche Photodetector

UV detection technology is extremely important in the military and civilian applications,which is Chinese urgent needs strategic technology.The signal transmission loss of ultraviolet photons is big.To meet the faint ultraviolet remote signal detection,the device must have high sensitivity,which requires the detector with high gain.In addition,the detection material itself also needs strong ability to inhibit out-of-band signal.The optical filter alone is difficult to achieve the ability.Meanwhile,AlGaN materials have the high capability of developing ultraviolet in/out-of-band rejection ratio and achieving high signal gain.Alx Ga1-x N material can modulate the band gap?3.42 ? 6.2 e V?by controlling the Al component,and the corresponding detection band covers ultraviolet to solar blind and deep ultraviolet bands.Besides,AlGaN has a higher specific detection rate,making it a very ideal ultraviolet detector materialHowever,to achieve high rejection ratio and high gain avalanche devices,the following key problems need to be solved: defect control in material epitaxy,avalanche ionization control in device design and fabrication,and dark current suppression.Therefore,this paper will discuss and solve these key scientific problems and technical bottlenecks from AlGaN material growth,avalanche detector design and preparation and other aspects:?1?As the aspect of the material epitaxy,the thesis introduced the preparation method of Nickel-based AlN self-assembled template.It discussed the nanoparticles size under different thickness of Ni metal,annealing temperature.Optimizing the process conditions,and study the relationship of Ni annealing self-assembly with dislocation distribution.Finally,the uniform AlN nanorods are successfully fabricated.Further employing self-assembled AlN nanographic template to prepare high-Al-content AlGaN.The template can realize AlGaN lateral epitaxy,effectively reduce the material dislocation,and improve the crystal quality.Besides,superlattice is also employed to filter dislocations.The AlGaN-based UV avalanche photodetector is further prepared by on the AlGaN nanographic template,showing excellent avalanche characteristics?2?As the aspect of the device design,based on the separate absorption and multiplication structure?SAM?,innovative design of the back-illuminated Al composition graded APD structure is proposed to realize the high gain and obtain supieror solar-blind ultraviolet detection performance.In addition,a photonic crystal filter is designed and theoretically elaborated with the integrated application of APD.Moreover,the front-illuminated polarization enhanced structure is proposed,and polarization and energy band engineering are effectively applied to increase the APD gain.Through numerical calculation of different structure of SAM APD structure,the precise control is carried out in different layer of SAM APD,which provides the design programs for performance improvement.?3?As the aspect of device preparation,the preparation technology of AlGaN was introduced.Novel mesa structure and graded Al compostion structure are proposed to improve device performance.Based on process preparation,a series of high performance devices are prepared,and the multiplication and reach-through mechanism of SAM APD are analyzed.As the following aspects:The back-illuminated AlGaN SAM APDs with different multiplication sizes were prepared.It was found that there was a trade-off between multiplication width and device performance.Different AlN templates were used to grow SAM structures.It was found that lower crystal quality would improve the dark current of APD,which was more likely to cause premature breakdown.The Al_0.1Ga_0.9N SAM APD based on triple mesa structure was prepared,and the high UV detection performance was realized.It proved that the triple mesa structure was conducive to optimizing the electric field distribution,reducing dark current and breakdown voltage.The mesa size effect of back-illuminated AlGaN APDs was studied,and the gradual Al component structure was applied to improve the crystal quality.The capacitive characteristics of the device were studied,and the reach-through mechanism of AlGaN SAM APD was directly observed.The significant decreasing trend of the capacitance reveals the depletion process of the n-type insertion layer and indicates the occurrence of the pass-through behavior.The reach-through mechanism of SAM APD is clearly revealed from both experimental and theoretical aspects,providing a direct method for extracting the reach-through voltage of the device.Ionization-enhanced solar-blind AlGaN heterostructure APD was prepared.By employing polarization engineering and component regulation to enhance impact ionization.A one-dimensional Si₃N₄/SiO₂ periodic crystal was creatively designed and integrated as an optical filter,effectively improving the solar-blind detection capability of APD.?4?As the aspect of performance improvement,the interdigital MSM ?-Ga₂O₃ solar-blind UV photodetector was prepared and compared.By introducing aluminum nanoparticles on the surface of the device,the device responsivity is increased by one order of magnitude.The surface potential distribution of KPFM was used to directly reveal the local electric field generation mechanism of Al nanoplasma and to prove the nanoplasmonically enhancement effect.