Preparation And Performance Study Of Bivalent Element Mg Doped And Zn-Mg Co-doped Ga₂O₃ Thin Films

Ga₂O₃ is a new type of ultra wide band gap semiconductor with a band gap of 4.9eV.Compared with the third generation semiconductor,it has the outstanding advantages of larger band gap,shorter absorption cutoff edge,lower growth cost,higher thermal and chemical stability,and owns a great application prospect in solar blind photodetectors and ultra-high voltage power devices.The power devices based on power semiconductor are made of transistors and diodes,and transistors consist of p-type and n-type semiconductors.Due to the oxygen vacancy,Ga₂O₃ usually exhibits n-type conductivity,and the conductivity can be improved by doping quadrivalent elements,however,the p-type Ga₂O₃ is difficult to obtain,which limits the application of Ga₂O₃ in devices.At present,Ga₂O₃ only can be used to make n-type Schottky barrier diode.The p-type Ga₂O₃ can be obtained by doping with divalent ions.The Mg:Ga₂O₃ and Zn-Mg:Ga₂O₃ films are prepared in this article,and the crystal structure,optical/electrical properties and photoelectric properties of the films are analyzed.The research content and conclusion is shown as following:1.As a kind of divalent elements,it's possible to obtain p-type Ga₂O₃ doped with Mg.The Mg:Ga₂O₃ films are prepared in this article.It's found that with the increase of Mg doping concentration,the diffraction peak shifts to lower angles.The results of XPS show that Mg exists in the form of Mg²⁺in the thin film lattice,and radius of Mg²⁺?0.72??is larger than that of Ga³⁺?0.64??,when Mg²⁺is incorporated into the Ga₂O₃ lattice instead of Ga³⁺,the interplaner distance?d?of the film increases.The films were annealed in N₂,and the diffraction peaks became sharper with the increase of annealing temperature,which indicated that the crystallization quality of Mg:Ga₂O₃ films increased after heat treatment.In addition,from the UV-vis absorption spectrum,as the Mg doping concentration increases,the absorption edges of the films red shift and the band gaps increase,because the band gap of MgO?7.8eV?is larger than that of Ga₂O₃?4.9eV?.The conductivity of Mg:Ga₂O₃ film worsens,which indicates that Mg doping makes the films insulated.2.Although Mg doping decreases the dark current of the Ga₂O₃ film,the band gap of Ga₂O₃film increase.As a kind of divalent elements,it's possible to obtain p-type Ga₂O₃ doped with Zn,in addition,doping Zn will reduce the band gaps of Ga₂O₃,because the band gap of ZnO?3.2eV?is smaller than that of Ga₂O₃?4.9eV?,Zn doping will reduce the band gap of Ga₂O₃ film.Therefore,different Zn/Mg alloying concentration ratios can change the band gap of the alloying?-Ga₂O₃ thin films.When the Zn/Mg doping concentration ratio is in a appropriate interval,the band gap of Zn-Mg:Ga₂O₃ thin film is close to the band gap of the pure?-Ga₂O₃ film.The Zn-Mg:Ga₂O₃ films with different Zn/Mg alloying concentration ratios are prepared in this article.It is found that the band gap of Zn-Mg:Ga₂O₃ film is close to that of pure Ga₂O₃ when the Zn/Mg alloying concentration ratio is about 1.35/1¹.39/1.The Zn-Mg:Ga₂O₃ film shows a low dark current?6.2×10^-1212 A at 1 V?,a high ratio of photo-to-dark current?1.8×10⁴?,a high responsivity of 25.7 mA/W?to 254 nm?,and a fast photoresponse time?less than 0.5?s for the rise time?.From the photoluminescence spectrum,the doping of Zn and Mg caused new emission peaks at 399 nm and 307 nm,respectively.It was found that the Zn and Mg doping in Ga₂O₃ film form the deep levels of Zn_Gaa and Mg_Ga,which are located at 0.79 eV and 1.00 eV above the valence band respectively.The results indicate that it is difficult to prepare highly conductive p-type Ga₂O₃ by doping with Zn and Mg impurities.