High-quality Epitaxy Material And Neotype Power Device Of ?-group Nitride

?-group nitride materials are widely used in light emitting devices and power devices,due to the improvement of the nitride epitaxial technology,device fabrication process and device structure.However,nitride materials still have very high defect density,which has great effect on the performance and reliability of the devices.Therefore,further improvement of the quality of nitride semiconductor materials is still one of the most significant problems in the world.In this dissertation,we investigate in depth the defect suppression and performance improvement of ?-group nitride semiconductor materials and power devices,such as GaN,AlGaN and AlN.We focus investigating several critical problems including:high quality GaN material epitaxy,high quality AlGaN material epitaxy,nitride heterostructure surface oxidation treatment technology research,high performance AlN/GaN enhancence-mode devices,high-quality AlN/GaN superlattice material growth and high performance AlGaN channel HEMT fabrication,and the performance degradation and reliability of AlGaN channel HEMTs.The main work and achievements are summaried as follows:1.Studied on the application method of silica micro-/nano-spheres monolayer film as dislocation block mask in nitride heteroepitaxial and the influence of preparation methods and various process parameters on the quality of the silica micro-/nano-spheres monolayer film.We innovatively introduced a polystyrene interlayer layer,which significantly improved the surface hydrophilicity of the substrate and the arrangement of micro-/nano-spheres,obtained a micro-/nano-spheres monolayer preparation process with uniform coverage.2.A novel epitaxial lateral overgrowth?ELO?method,partly-contacted ELO?PC-ELO?,is proposed to lower the dislocation density of GaN growth.The contact window has been introduced in the overgrowth area innovatively to eliminate the wing tilt and reduce the dislocations,and the crystal orientation of the wing area has been corrected by contacting with the seed layer,the principle of dislocation elimination is explained in detail as well.Besides,two implementation methods of PC-ELO,photolithography based implementation and photolithography free silica micro-/nano-sphere monolayer based implementation,are proposed to realize PC-ELO.Finally,a GaN heteroepitaxial material with a low dislocation density of 6.5×10⁷ cm^-2 is obtained by using a monolayer of 1?m silica microspheres.3.A novel high-quality AlGaN heteroepitaxy method,high-quality Ga-rich AlGaN grown on trapezoidal patterned GaN template?TPGT?,is proposed to improve low Al component AlGaN heteroepitaxy.TPGT with low dislocation density is obtained by the selective growth method,and high quality low Al component AlGaN material is grown based on the ultra-short period AlN/GaN superlattice structure,which effectively reduces dislocation density,greatly improves the growth rate ratio of AlGaN,relaxes mismatch stress,and suppresses the cracking of epitaxial layer.Finally,for the 27.8%component Al AlGaN,the dislocation density of AlGaN epitaxial layer is reduced from 2×10⁹ cm^-2 to 2×10⁸ cm^-22 using TPGT,the complete relaxation of the misfit strain inhibits cracking of AlGaN layer.In addition,the specific growth rate of horizontal and vertical is up to 4.79,which is a very high growth rate of horizontal and vertical ratio for this specific AlGaN material with Al component of 27.8%.4.The effect of surface state of surface natural oxidation and oxygen plasma oxidation in the heterostructure on 2DEG is investigated.A method based on low power oxygen plasma treatment?LP-SOT?is proposed to change the surface density distribution and improve the surface potential,thus controlling the 2DEG surface density of the channel.The barrier layer of a heterostructure with protection of GaN cap will not be destroyed by short and low power processing conditions.This method shows high application value in the ultrathin barrier heterostructure represented by AlN.5.Enhancement-mode AlN/GaN HEMTs are realized using LP-SOT,the manufacturing process of the device are introduced,and the basic characteristics along with trap effects of the device are analyzed in detail.The device shows a maximum drain current of up to 1.36A/mm and a positive threshold voltage of+0.2 V.Moreover,the gate leakage current of the devices with LP-SOT is reduced by 1 to 2 orders of magnitude than the gate leakage current of the devices without LP-SOT.6.The basic characteristics of AlN/GaN superlattices are studied theoretically,including the energy band structure,breakdown field strength,and 2DEG low field electron mobility of alloy AlGaN and AlN/GaN superlattice AlGaN as AlGaN/AlGaN heterostructure of channel layer.The results show that comparing with alloy AlGaN channel HEMTs,the AlN/GaN superlattice channel HEMTs have almost the lower breakdown field strength and the similar2DEG concentration,but the electron mobility of 2DEG is superlattice channel is obviously higher.Finally,we also discuss the effect of strain on the 2DEG characteristics of the alloy AlGaN channel and the AlN/GaN superlattice AlGaN channel HEMT structures.We proposed an AlN/GaN superlattice channel HEMT heterostucture based on the graded Al content buffer layer and achieved the high performance AlN/GaN superlattice channel HEMT heterostucture with high electronic mobility and high 2DEG density based on this layer structure using epitaxial growth.7.High-performance alloy AlGaN channel HEMTs are demonstrated.A maximum drain current of 849 mA/mm,a peak transconductance of 108 mS/mm,an electron mobility of 807cm²/V·s,and an I_on/I_offff of up to 10⁹ are realized,as far as we know,they are very superior electrical characteristics among reported AlGaN channel HEMTs.The proposed devices show comparable drain current and peak transconductance with GaN channel HEMTs,furthermore lower gate leakage current and higher breakdown voltage are obtained.Thus,alloy AlGaN channel HEMTs with low Al component show great application prospects in high-power power electronic devices.8.A novel high-performance AlGaN channel HEMTs,AlN/GaN superlattice AlGaN channel HEMTs,are realized using AlN/GaN superlattice Al_0.10Ga_0.90N instead of perforated alloy Al_0.10Ga_0.90N as the channel layer.It is the world's first nitride superlattice channel HEMT device.The AlN/GaN superlattice AlGaN greatly improves the ordering of AlGaN alloys,reducing the disorder scattering of the channel electrons,so as to increase channel mobility from 807 cm²/V·s to 1179 cm²/V·s.Compared with the alloy AlGaN channel HEMTs,the maximum drain current?1020 mA/mm?and peak transconductance?118mS/mm?of the superlattice AlGaN channel HEMTs have been significantly improved without deteriorating other electrical characteristics.