Heteroepitaxial Integration Of Functional Oxide Thin Film Toward Enhancement-mode HEMT Device

Enhancement-mode?E-mode?GaN high electron mobility transistor?HEMT?palys a key role in next generation power electronics for advantages of high voltage,high frequency,high power and small size.Based on novel device physical mechanis m,integration of oxides with ferroelectric or p-type semiconductor functionality on Al GaN/GaN heterostructure to serve as the gate layer could offer new solution for high performance E-mode HEMT.However,due to different crystal structure between oxide and GaN,diversity of surface and interface for multilayer film and complexity of interfacial coupling mechanism,series of obstacles such as integration of functio na l oxide thin films with GaN,unclear device physical mechanism and device feasibil it y hinder the application of functional oxide gate E-mode HEMT.Based on above problems,high quality integration of complex functional oxides on GaN was realized by designing interfacial buffer layers,device physical mechanism and feasibility of functional oxide gate E-mode HEMT was clarified by revealing interfacial coupling effect between specific functions of oxides and two-dimensional electron gas?2DEG?at Al GaN/GaN interface.?1?Epitaxial integration of functional oxides on GaNBased on lattice matching epitaxial growth mechanism,high quality integration of complex functional oxides on GaN semiconductor was realized by designing specific interfacial buffer layer.Using pulse laser deposition?PLD?method,designed La_0.5Sr_0.5Co O₃/Ti O₂buffer layers could tremendously reduce the interfacial lattice mismatch,which induced the epitaxial integration of high performance perovskite0.7Pb(Mg_1/3Nb_1/3)O₃-0.3Pb TOi ₃?PMN-PT?ferroelectric thin films on wurtzite GaN semiconductor;By designing spinel Co Fe₂O₄ ferrimagnetic buffer layer,epitaxia l growth of perovskite Ba TOi ₃?BTO?ferroelectric thin films on wurtzite GaN was realized,and the constructed Co Fe₂O₄/Ba TOi ₃ epitaxial multiferroic heterostructure on GaN displayed great ferroelectric and ferromagnetic characteristics.By designing cubic Ti N,wurtzite Ti and spinel Mg Al₂O₄ buffer layers with different crystal structure,high quality perovskite Sr TOi ₃ dielectric thin films was epitaxially grown on GaN,which offered great template for integration of various complex functional oxides on GaN.?2?Ferroelectric oxide gate E-mode HEMTBa Ti O₃/Mg O/Al GaN/GaN/Si ferroelectric-semiconductor heterostructure was designed and constructed by PLD method to reveal interfacial coupling mechanis m.Upward ferroelectric self-polarization of BTO was induced by the formation of space charge region at BTO/GaN interface,which tremendously enhanced threshold voltage.Strong interfacial polarization coupling effect was revealed between ferroelectr ic polarization of BTO and 2DEG at Al GaN/GaN interface,and successive modulation of threshold voltage from-0.4 V to+3.2 V was detected by regulating polarization state of BTO,which directly confirmed feasibility of ferroelectric oxide gate E-mode HEMT.Hf_0.5Zr_0.5O₂?HZO?ferroelectric thin film was designed to serve as the gate layer of HEMT,and high quality HZO/Mg O/Al GaN/GaN/Si epitaxial heterostructure was constructed.Successive modulation of threshold voltage from-3.8 V to+3.2 V was realized by regulating ferroelectric polarization state of HZO,and superhigh threshold voltage?+5.5 V?was detected.HZO/Mg O/Al GaN/GaN/Si heterostructure displayed high threshold voltage,weak depolarization effect and great semiconductor process compatibility,which was suitable to develop high performance ferroelectric gate E-mode HEMT.?3?P-type oxide gate E-mode HEMTP-type Li-doped Ni O thin films with high quality,ultrahigh hole concentration and wide band gap were epitaxially grown on Al GaN/GaN to explore p-type oxide gate E-mode HEMT.Band alignment at p-oxide/GaN interface was revealed to be key issue that determined threshold voltage,that is,the band energy level difference between conduction band energy level of GaN and valance band energy level of p-type oxide determined the depletion capacity of p-type oxide on 2DEG at Al GaN/GaN interface,and threshold voltage was restricted by bad band alignment at intrinsic p-type oxide and GaN.Based on design principle of p-type layer,modulation doped p-type oxide gate layer from intrinsic n-type oxide would possess greater potential to enhance threshold voltage than intrinsic p-type oxide.