First-principle Studies On P-type Doping Gallium Oxide Crystal

Wide band gap semiconductors have become one of the hottest topics of the day due to their unique properties and application potentials in various fields.Among them,?-Ga₂O₃ crystal as a fourth generation wide band gap semiconductor has shown excellent performances in many fields,including high-temperature gas sensors,deep ultraviolet optoelectronic devices and ultra-high voltage power devices.In order to grow n-type and p-type ?-Ga₂O₃ crystals of high quality and high carrier concentration,doping is regarded as an important method.After years of research,n-type semiconductors have been successfully prepared and the carrier concentration can be controlled to a certain extent.However,the preparation of p-type semiconductors is still a major problem,which also restricts its applications as devices.By continuous efforts both in theory and experiment,it is clarified that the difficulty in p-type doping can be attributed to three major aspects:?1?self-compensation effect by n-type background carriers,?2?lack of shallow-level acceptors,and?3?passivation of doped acceptors.In this thesis,the first two issues aforementioned which cause the difficulty of p-type doping of ?-Ga₂O₃ crystal have been discussed based on first-principle calculations.Effects of intrinsic defects,single metal doping as well as metal-nonmetallic co-doping have been discussed,and some possible ways to realize the growth of p-type doped ?-Ga₂O₃ crystal have been put forward.The optimal configurations of different defected and doped systems have been determined by the calculation of the formation energy.Based on those results,electronic properties have been discussed in detail.The calculation indicates that Gai,GaO and GaiVO show n-type conductivity,whereas VGa,GaiVGa and OiVGa show p-type character.In addition,n-type defects prefer Ga-rich enviorment while p-type defects prefer O-rich condition.Therefore,we believe that O-rich condition is better for the growth of p-type Ga₂O₃ semiconductors.Our calculations on seeking p-type shallow-level acceptors indicate that Na,Mg,Ca,Cu,Ag,Zn and Cd are all potential p-type impurities through analysing the formation energy and the density of states.Subsequent experiments should be carried out for a further study.In addition,it is found that the formation of the co-doped ?-Ga₂O₃ crystal was lower than that of single doping.Moreover,p-type conductivity was generally exhibited in all co-doped systems due to the charge-compensating effect.Therefore,metal-nonmetallic co-doping could be an efficient way to deal with the difficulty in the growth of p.-type?-Ga₂O₃ semiconductors.Moreover,we have also calculated the absorption spectra of metal-doped?-Ga₂O₃.Although a redistribution of the main absorption peakhas occurred in most cases,the absorption edge remained almost unchanged.Therefore,doping does not affect its application in the field of deep ultraviolet optoelectronic devices.In addition,we have discussed the potential of Sc-N codoped ?-Ga₂O₃ for photocatalytic overall water-splitting.