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Study On Material Growth And Photo-electric Characterizations Of Back-illuminated MIS Structure AlGaN Solar-blind Ultraviolet Photodiodes

Posted on:2019-06-12Degree:MasterType:Thesis
Country:ChinaCandidate:W Y HanFull Text:PDF
GTID:2348330545494552Subject:Condensed matter physics
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With the development of science and technology,ultraviolet detection technology has been widely applied in military and civil fields.AlGaN solar-blind UV detector has the advantages of solid state,intrinsic cut-off,small working voltage and stable physical and chemical properties.AlGaN materials have directly widen band gap with a tunable bandgap which ranges from 3.4 to 6.2 eV,covering solar-blind ultraviolet wavelength,which are the ideal materials for making solar-blind ultraviolet detectors.In traditional research,researchers are focused on p-i-n structure AlGaN-based UV-PD,because of its intrinsic advantages: low dark current,high speed of response,and apt to integrate with the Si-based read-out integrated circuit using flip-chip technique to make focal plane arrays.However,high performance p-type doping of AlGaN with high Al content is difficult to obtain,as a result of the high activation energy for the passive acceptor of the magnesium atom;This material suffers from lattice mismatch and thermal expansion mismatch,because of the difference for lattice constant and thermal expansion coefficient between the sapphire substrate and the epitaxial layer;It is difficult to form good ohmic contact on p-AlGaN that affects the transport of photongenerated carriers.These factors restrict its development seriously.Although p-GaN can be adopted to overcome the influence of the poor performance p-AlGaN and solve the transport problem of photo-generated carriers,the introduction of p-GaN layer will enable the device to have a spectral response at the near-ultraviolet band,which does not fully meet the requirement of the solar-blind UV-PD.So we make the backilluminated metal-insulator-semiconductor(MIS)structure AlGaN-based photodiode,because it not only has the same advantages as the p-i-n structure photodiode,but also solves the technical bottleneck caused by p-AlGaN material.However the spectral response and EQE of back-illuminated solar-blind AlGaN-based Schottky photodiodes are always poorer than that of back-illuminated p-i-n junctions due to the smaller builtin electric field of Schottky diodes and the narrower depletion region.In this paper,wo focus on improving responsivity and external quantum efficiency of the AlGaN solarblind ultraviolet detectors based on regulating polarization electric field at the heterointerface and regulating built-in electric field in light absorption region.In this paper,high quality AlN buffer layer was grown on(0001)sapphire substrate by metal-organic chemical vapor deposition(MOCVD).Then,on the basis of the traditional MIS structure,a thin n-AlGaN layer with Al content gradually decreasing was introduced in the heterogeneous interface to regulate the polarization electric field.And,we introduced a homogeneous n-AlGaN interlayer in the light absorption layer to regulate the electric field in the light absorption region,and verified through the simulation analysis and experiments.We also optimized the properties of MIS structure devices through the comparison experiments of the metal electrodes forming different Schottky contacts.The main achievements are as follows:1.On the basis of traditional method of "two step growth",we introduced medium temperature AlN layer into the buffer layer,stopping further extension of the dislocation in the buffer layer efficiently,and releasing the stress to obtain high quality AlN template.2.A thin n-AlGaN layer with Al content gradually decreasing is used as an interlayer of the heterojunction,regulating the polarization charges density to decrease the polarization electric field,resulting to reducing the dark current of the detectors.Meanwhile,the thin n-AlGaN layer also effectively released the stress of the light absorption layer,improving the crystal quality of the light absorption AlGaN material.3.A homogeneous n-AlGaN interlayer is introduced into the i-AlGaN insulation layer.The presence of the homogenous n-AlGaN interlayer increased the electric field of the light absorption region,in favor of the separation and transport of the photogenerated carriers,and improving the photoelectric characterizations of MIS detectors.4.Through the comparison experiments of the metal electrodes forming different Schottky contacts,we optimized the photoelectric characterizations of MIS detectors.The device has response wavelength ranged from 255 nm to 280 nm,and presents a peak responsivity of 0.115 A/W at 270 nm,corresponding to external quantum efficiency(EQE)of 53% under zero-bias,and an ultraviolet/visible rejection ratio is more than three orders of magnitude.Moreover,a peak responsivity of 0.154 A/W,corresponding to an EQE of 70.6% is achieved at reverse bias of 3 V,and a response speed is around 24 ?s.The results of this paper laid a foundation for overcoming the problems caused by high Al content p-AlGaN in p-i-n structure.
Keywords/Search Tags:Photoelectric detector, Solar-blind ultraviolet, AlGaN, MOCVD, Metalinsulator-semiconductor
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