First-principles Study On P-type Doping Wide Band Gap Semiconductor β-Ga₂O₃

With the development of science and technology,new wide band gap semiconductor materials with high performance and low cost have become the focus of research.β-Ga₂O₃is an ideal material for ultra-high voltage switching power devices with the advantages of high temperature resistance and radiation resistance.Moreover,β-Ga₂O₃has a wider band gap than SiC and GaN,and its power devices have higher V_br efficiency than SiC and GaN devices.However,β-Ga₂O₃ also has an obvious defect,i.e.,it is difficult to prepare p-type crystals,which greatly limits the development of this new material.Fabricating p-typeβ-Ga₂O₃ with shallow acceptor levels is vital to the application ofβ-Ga₂O₃ based devices.Herein,we propose a potential approach,（electron-poor metal,N）co-doping,to effectively decrease the acceptor levels.And further study on this basis,the selected metal of shallow level acceptor impurities will be separately co-dopedβ-Ga₂O₃ with non-metal（fluorine,sulfur,chlorine）respectively.The main research results of this paper are as follows:（1）Under oxygen-rich atmosphere,the formation energy of oxygen vacancy which inhibits p-type conduction increases,while the formation energy of metal-dopedβ-Ga₂O₃ decreases.Among them,the formation energy of Mg-dopedβ-Ga₂O₃ is the lowest and the easiest to achieve doping,while the formation energy of Cs-dopedβ-Ga₂O₃ with large atomic radius is the largest and the most difficult to achieve doping.More importantly,（metal dopant with p orbitals,N）co-doping hinders the formation of O-vacancy which limits the formation of p-typeβ-Ga₂O₃,while（metal dopant with d orbitals,N）co-doping promotess the formation of O-vacancy.（2）The（electron-poor metal,N）co-doping is easier to be realized compared to the pure N doping forβ-Ga₂O₃.Moreover,partial co-doping further shifts up the Ga-O bonding orbitals and down the dopant-O anti-bonding orbitals and the unoccupied p orbitals of N and O ions,thus the acceptor levels can be significantly decreased when the pure metal doping is replaced by the co-doping method.The acceptor levels of（Mg,N）,（Cu,N）,（Zn,N）,（Ag,N）and（C_S,N）co-doped unitβ-Ga₂O₃are as low as 0.16,0.43,0.01,0.45 and 0.11 e V,respectively.These results suggest that（metal,N）co-doping might be a potential way to achieve an effective p-typeβ-Ga₂O₃.In addition,the higher the doping concentration,the lower the acceptor level introduced.（3）The co-doping mechanism can effectively reduce the formation of gallium oxide oxygen vacancies relative to the metal doping mechanism.The co-doping of the electron-poor metals（Mg,Zn,and Ag）and the three nonmetals（F,Cl,and S）can make the supercellβ-Ga₂O₃crystal show the characteristics of p-type conductivity.In addition,the p-type effect of fluorine and metal co-dopedβ-Ga₂O₃ crystal is better than that of two non-metals,chlorine and sulfur.Among them,the acceptor levels of（Mg,F）and（Zn,F）co-doped supercellβ-Ga₂O₃ are the lowest,which are 0.55 e V and 0.64 e V,respectively.Moreover,their light absorption properties are also excellent.However,its doping formation energy is slightly higher than that of（Mg,N）and（Zn,N）co-doped supercellβ-Ga₂O₃,that is,the effective carrier concentration is not higher than that of（Metal,N）co-dopedβ-Ga₂O₃.From the perspective of substitution defect formation energy and oxygen vacancy formation energy,（Mg,N）and（Zn,N）co-dopedβ-Ga₂O₃ are easier to achieve p-type.（4）According to the Bard charge layout analysis,the difference of electronegativity between the two doping elements in the（metal,nonmetal）co-doped system needs be as large as possible,such as（Mg,F）and（Zn,F）co-dopedβ-Ga₂O₃.Which is conducive to making the dopant easy to lose electrons and exhibit the properties of shallow acceptor level.