Theoretical Exploration Of Mg-O/Ca-O Co-doping To Improve The P-type Conductivity Of GaN

As a representative of the third generation wide-bandgap semiconductors,GaN has been widely used in military and civil applications,such as microwave devices,electronic devices,and light-emitting devices.This is mainly due to the many advantages of gallium nitride with large band gap width,large critical breakdown electric field,high saturated electron drift speed,and stable chemical properties.Among them,in the application of high-performance blue light diodes,one of the most urgent and challenging tasks is to obtain high p-type conductivity of gallium nitride.Thus far,Mg is still the most effective p-type dopant for GaN.However,Mg-doped GaN still demonstrates some disadvantages,such as the existence of unavoidable V_N and Mg_i,and the deeper transition level of Mg_Ga,which greatly reduce the p-type conductivity of Mg doping gallium nitride.Co-doping is the introduction of two or more dopants into the host material,which not only increases the solubility of the required dopant,but also improves the performance of the host material through the interaction between the dopants.Co-doping can be divided into two ways: dopants are incorporated simultaneously and successively into the host material.Alternate doping is able to make dopants meet each other and form composite defects with respect to simultaneous doping.First-principles calculations have become a useful tool,not only for understanding experimental observations,but also for designing new materials with ideal properties.For semiconductor materials,theoretical calculation selecting appropriate dopants provides theoretical basis for experimental research and development of high conductivity materials.Based on the first-principles calculations,in this thesis,the doping method to further improve the p-type conductivity of gallium nitride is explored.The main research contents are shown in the following:?1?The stable defects of the wurtzite-based GaN doped by Mg and Mg-O defect systems were thoroughly calculated,and their electronic structures were carefully analyzed.We have found that doping O into GaN and then doping with Mg can eliminate the negative effect of nitrogen vacancies?V_N?on the p-type conductivity,and also reduce the defect formation energy and transition energy of Mg substituted Ga(Mg_Ga).At the same time,the introduction of O also inhibits the formation of Mg intermediate?Mg_i?.However,the simultaneous doping of two dopants of Mg and O into GaN indicates that V_N could not be eliminated,and that defect formation energy of acceptor complex defect(Mg_Ga-O-Mg_Ga)is also higher than acceptor complex defect(Mg_Ga-O_VN-Mg_Ga),making the doping more difficult.?2?The stable defects of the wurtzite-GaN doped by Ca and Ca-O defect systems were calculated in detail and their electronic properties were analyzed.Studies have found that Ca-doped GaN exhibits magnetic,but its p-type conductivity is poor.The p-type conductivity of GaN can be further improved by doping with O and then doping Ca.Moreover,compared with Mg-O co-doped gallium nitride,it can better suppress the adverse effects of gap defects on p-type conductivity.The content of this thesis provides a new strategy for further improving the p-type conductivity of GaN.