Preparation And Characterization Of ?-Ga₂O₃ Films On SiC,GaN And GGG Substrates

?-Ga2O3 is an ultra-wide band gap transparent oxide semiconductor material,which has excellent thermal stability,physicochemical stability and high breakdown field strength.It has wide application prospects in the fields of high temperature and high voltage electronic devices,solar blind area ultraviolet detectors and transparent thin film transistors.Therefore,Ga2O3 material has become one of the research hotspots at present.?-Ga2O3 thin films prepared by magnetron sputtering,electron beam evaporation and other traditional processes are almost amorphous and polycrystalline with poor crystalline quality,which can not meet the requirements of high quality semiconductor optoelectronic devices.At present,the price of ?-Ga2O3 single crystalline wafer is very expensive,and the thermal conductivity of ?-Ga2O3 material is relatively poor.So it is necessary to carry out the research work of heteroepitaxial growth of ?-Ga2O3 thin films.In this paper,?-Ga2O3 thin films were prepared by metal organic chemical vapor deposition(MOCVD)on SiC,GaN and GGG substrates,and then annealed at different temperatures.The effects of annealing temperature on the structure and optical properties of the films were studied.In the experiment,high purity Ga(CH3)3 was used as Ga organic source,high purity O2 as oxidant,ultra-high purity N2 as carrier gas.The molar flow rate of organic source was 8.2×10-6mol/min,and the substrate temperature was 660 ?.Annealing treatment was carried out in air for 1 hour at 800 ?,900? and 1000 ?,respectively.?-Ga2O3 epitaxial single crystal films were successfully prepared on SiC(0001),GaN(0001)and GGG(110)substrates.The main research work and results are as follows:1.Preparation and properties of ?-Ga2O3 films on SiC(0001)substrates:The structure,surface morphology and optical properties of Ga2O3 films on SiC(0001)substrates were studied.The structure analysis shows that the Ga2O3 films before and after annealing at 800 ?C are amorphous.The films annealed at 900 ?have better crystalline qualities,grown along[100]single orientation.The out-of-plane growth relationship between ?-Ga2O3 film and SiC is?-Ga2O3(100)||SiC(0001).The transmittance of the sample annealed at 900 ? is about 76%in the visible range.When the annealing temperature reaches 1000 ?,the film has a polycrystalline structure and the crystalline quality is obviously deteriorated.2.Preparation and properties of ?-Ga2O3 films on GaN(0001)substrates:The surface morphology,elemental composition,lattice structure,epitaxial relationship and optical properties of Ga2O3 films on GaN(0001)substrate were studied.XRD analysis showed that the gallium oxide films before and after annealing at 800 ? were amorphous.The crystalline quality of the films annealed at 900 ?was the best.The films were ?-Ga2O3 grown along[100]single orientation.When the annealing temperature reaches 1000 ?,the film has a polycrystalline structure and the crystalline quality is obviously deteriorated.For that sample annealed at 900 ?,the out-of-plane epitaxial relationship between ?-Ga2O3 film and GaN is?-Ga2O3(100)||GaN(0001),and the in-plane epitaxial relationship is?-Ga2O3<010>||GaN<1210>and ?-Ga203<001>||GaN<1010>.XRD ? scanning analysis shows a tripartite domain structure existed inside the ?-Ga2O3 film.That is due to the triple symmetry of GaN(0001)substrate along the[100]direction.The optical transmittance of the sample is higher than 78%in the visible range.3.Preparation and properties of ?-Ga2O3 films on GGG(110)substrates:The lattice structure,epitaxial mechanism,optical properties and photoluminescence mechanism of Ga2O3 films on GGG(110)substrate were studied.The structure analysis shows that the as-deposited samples are amorphous,and the films annealed at 1000 ? are polycrystalline.The films annealed at 800 ? and 900 ? were ?-Ga2O3 grown along[100]single orientation,and the films annealed at 900 ? had the best crystallization quality.The epitaxial relationship between?-Ga203 film and GGG substrate is ?-Ga203(100)||GGG(110),?-Ga2O3<010>||GGG[001]and ?-Ga2O3<001>||GGG[110],The transmittance of the sample is higher than 84%in the visible range.The optical band gaps of the films before and after annealing at 800 ?,900 ?,1000 ? were 4.83,4.76,4.60 and 4.74 eV,respectively.At room temperatures,several photoluminescence bands can be observed in the wavelength range of 330-520 nm for the films annealed at 800 and 900 ?.For the samples annealed at 900 ?,six luminescence peaks were observed at 348.7 nm,392.6 nm,403.9 nm,429.1 nm,452.6 nm and 484.1 nm by Gaussian fitting analysis,respectively,which were attributed to electron transition between the conduction band,valence band,donor and acceptor energy levels formed by defects in the films.