| In the past two decades,GaN,SiC,Ga2O3 and other third-generation semiconductor materials with band-gap widths greater than 2.3 eV have been widely studied.This kind of material has the advantages of wide band gap,high electric field breakdown strength and saturated electron drift speed,as well as good chemical and thermal stability,and has been applied in some military or commercial systems.Such as satellites or avionics,then radiation hardness is a key requirement.GaN is currently used on NASA satellites.Previous studies on radiation mainly focus on GaN devices as a whole,and there is little comparison on the radiation resistance performance of p-GaN and n-GaN films,which are important components of power devices.In addition,β-Ga2O3 with a wider band gap has a higher critical field,and the wider the band gap,the greater the potential of a specific semiconductor for high voltage applications.Therefore,the increase of band gap has a great effect on the advantage power.Therefore,in addition to the research on the radiation effect of gallium nitride,this paper carried out a study on the radiation effect of β-Ga2O3.Through the preliminary research work,it was found that the radiation resistance of gallium oxide power devices has a certain basis,but the radiation resistance of its optical devices needs to be supplemented.In this paper,p-GaN and n-GaN films with common GaN devices as reference thickness were prepared to compare and study the electrical properties before and after irradiation.β-Ga2O3 was used as the material to prepare MSM type photodetectors.Ta ion irradiation with the same energy and different doses was used to irradiation photodetectors.The changes before and after were analyzed and compared,and the first principles calculation was used to verify the analysis.The main research results are as follows:1.Irradiation effects of high-energy X-ray and 2 MeV proton with the ionizing effect and displacement effect on GaN thin films are investigated and compared.For fundamental analysis,the electrical properties of PGaN and N-GaN separated from power device are both analyzed.Hall and circular transmission line model measurements proved that the electrical properties of P-GaN were improved under high dose X-ray irradiation due to the Mg-H bond breaking.In detail,under the X-ray dose of 100 Mrad(Si),the specific contact resistance ρc of P-GaN has decreased by 30%and the hole carrier concentration also increase significantly.In addition,for atom displacement damage effect of 2 MeV proton of 1×1013 p/cm2,the electrical properties of P-GaN showed obvious degradation but N-GaN remained unchanged.Our work revealed that the X-ray irradiation can be treated as an effective method to improve the electrical properties of P-GaN thin films,and P-GaN was proved to be more sensitive to irradiation than N-GaN thin film.2.The photoresponse behavior of β-Ga2O3 photodetectors under 254 nm and 365 nm UV light was compared.Under 254 nm UV irradiation,the photocurrent firstly decreased and then increased with the increase of irradiation dose,which was opposite to that under 365 nm UV irradiation.According to the first-principles calculation,the mechanism is mainly related to the band modulation caused by crystal defects.Although the change of band gap reduces the photocurrent of the device under irradiation,the oxygen vacancy generated by irradiation and the generated defect level enhance the photocurrent.Under 254 nm and 365 nm UV detection,the performance of the photodetectors is obviously improved due to the introduction of defect levels in the β-Ga2O3 band gap.The explanation of defect level assisted photocarrier band transition is proposed.Different from Si or GaAs,the introduction of defect levels in the band gap produces many interesting phenomena in ultra-wide-band gap semiconductors such as Ga2O3,which is worthy of systematic study. |
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