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Ammonothermal Growth Of GaN And Characterization Of Its Physical Properties

Posted on:2021-05-14Degree:DoctorType:Dissertation
Country:ChinaCandidate:T K LiFull Text:PDF
GTID:1368330602496397Subject:Microelectronics and Solid State Electronics
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Bulk,single crystal Gallium Nitride(GaN)crystals are essential for enabling high performance GaN devices by providing high quality,large,arbitrarily oriented single crystal GaN substrates.Due to its merits like growth in equilibrium conditions,scalability,the ammonothermal method is considered as one promising technology to realize industrialized production for bulk GaN fabrication.In this dissertation,the ammonothermal facility and the growth characteristics of GaN crystal grown by ammonothermal method are studied.The mineralizer was investigated and optimized,and high quality GaN bulk single crystal was obtained using self-developed ammonothermal growth system.The growth characteristics of various polarity seeds are studied.The main results are summarized as follows:1.Manufacturing a self-developed ammonothermal growth system.The growth temperature of the system can reach 600?,and the growth pressure can reach 300 MPa.Through the combination of simulation and experiment,the opening rate of baffle and the structure of seed-frame were designed,so the internal temperature field and flow field of autoclave are optimized.The system pressure deviation is as low as 0.5Mpa/d,which verifies the stability and reliability of the facility.This work provides a reliable guarantee for the study of ammonothermal GaN growth.2.Mineralizer optimization and impurity incorporation investigation.The growth of GaN crystal using NH4Cl as mineralizer and its corrosion to autoclave were studied.High quality c-plane,nonpolar and semi-polar GaN bulk single crystal was abtained by adding KNH2 as mineralizer.The influence of adding semi-sealing lining and annealing treatment on impurities were studied.The results show that the concentration of impurities from the autoclave material can be effectively reduced by adding semi-closed liner during the short period growth.3.The growth behaviors of various crystal planes were investigated.GaN crystals were grown on non-polar and semi-polar HVPE GaN seeds by basic ammonothermal method.The different surface morphology regimes were observed with the surface features including hillock,slate and elliptical sphere like.The growth rate and evolution process of various planes of as-grown GaN crystals were characterized through the cross section.According to the growth rate,the Wulff's rule of GaN grown by ammonothermal method was constructed to predict the equilibrium morphology of crystal growth.The dominant facets of GaN crystals ultimately will be the non-polar m-planes,the {10-11} semi-polar planes and the polar(000-1)plane by analyzing morphological evolution of crystal shape using kinetic Wulff's rule.4.Stress distributions of GaN crystals were grown on non-polar and semi-polar HVPE GaN seeds.Stress distributions were investigated in cross-section of(11-20)plane,(10-10)plane,(20-21)plane and(10-11)plane GaN crystal.The CL images show cross-section information clearly and each examined object consisted of HVPE seed and ammonothermal GaN.The impurity concentration and free carrier concentration were estimated by secondary-ion mass spectroscopy(SIMS)and Hall.Moreover,Raman spectroscopy was used to study stress distribution in the cross section.Shifts of E2(high)phonon lines were analyzed to analysis the stress.Our results indicate that the stress is about 35 MPa in bulk GaN and the stress is less than 60 MPa in the interface of Am-GaN.5.The characteristics of different growth regions of ammonothermal bulk single GaN crystal.According to different optical properties,the growth region can be divided into four regions:Ga-polar,N-polar,wing1 and wing2.The stress distribution in different regions was further characterized by Raman spectroscopy,among which there is about 40 MPa compressive stress in the wing2 region compared with other regions.Further study is needed for the formation of the wing2 region.The growth rate is fastest of ammonothermal GaN bulk single crystal in a-direction.In order to enlarge the size of seed crystal,the lateral growth of a-direction should be utilized.
Keywords/Search Tags:Gallium Nitride, ammonothermal method, mineralizer, growth behavior, stress distribution
PDF Full Text Request
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