Study On The Polarization-induced Doping Of Group-Ⅲ Nitride Semiconductor Materials

Group Ⅲ nitrides（Al N,Ga N,In N and their alloys）are one of the most important semiconductor materials in the field of optoelectronics research in recent years,and it has been widely used in lighting,display,etc.And there is also a huge potential market in this filed,such as the emerging nitride deep ultraviolet LED,Micro LED and high-speed LED that can be used in sterilization,micro-display,visible light communication and so on.However,there are still some constraints to the high-performance development of group-Ⅲ nitride light-emitting devices.For example,there are certain difficulties both in p-type and n-type doping of Al N and Al Ga N with high Al components.The polarization-induced doping method provides a feasible way for effective p-type and n-type doping of nitride semiconductors.However,there is currently a lack of in-depth understanding of the polarization induced doping theory of group Ⅲ nitride alloy materials in relevant research work,and there are some important issues that need to be studied urgently.For example,what are the differences in polarization induced doping efficiency among different nitride alloy materials,and how key factors such as lattice strain,film thickness,component gradient,and lattice polarity affect polarization induced doping in nitride alloy materials.To this end,we carried out a theoretical research on polarization induced doping of group Ⅲ nitride materials,and established a theoretical model of polarization induced doping of group Ⅲ nitride semiconductors.Based on this,we conduct some experimental studies on multi-gradient path polarization-induced p-type doping and n-type doping in group Ⅲ nitride semiconductors,established the composition gradient growth process of nitride materials with different gradient paths,and realized the polarization-induced doping of nitride materials with different gradient paths.Furthermore,the average polarization intensity change rate of the gradient materials of different gradient path components was calculated from the experimental data,and compared with the theoretical value.Showed that the experimental values are consistent with the theoretical values,which verifies the accuracy and practicability of the theory of polarization-induced doping.The relevant research results are beneficial to the design of high-efficiency doping of nitride materials and high-performance nitride semiconductor devices.The main research contents of this paper are as follows:1.Theoretical research on polarization-induced doping of nitride semiconductor materials.The parameters such as the spontaneous polarization intensity and piezoelectric polarization constant of the nitride material were obtained by the first principle calculations.Furthermore,the change rate of polarization intensity of nitride semiconductor materials with different components under different strain conditions was calculated,and the theoretical model of polarization-induced doping of nitride semiconductors was constructed.On this basis,the differences in the polarization-induced doping efficiency of different nitride alloy materials are clarified,and the effects of lattice strain,film thickness,component gradient and lattice polarity on the polarization-induced doping efficiency of nitride alloy materials were analyzed firstly.2.Study on the polarization-induced n-type doping of compositionally graded nitride films.Nitrogen-polar In_xGa_1-xN with increasing In composition（x=0→0.15）and metal-polar Al_xGa_1-xN with increasing Al composition（x=0.13→0.2）prepared by metal organic chemical vapor deposition（MOCVD）,realizing the polarization-induced n-type doping of nitride alloy materials with the above-mentioned gradient path.At room temperature,the electron concentrations in graded In Ga N and Al Ga N are 1.97×10¹⁸cm^-3and 1.2×10¹⁸cm^-3,respectively.And the electron concentration changed little with temperature ranging from 90 K to 300 K,indicating that the electrons were mainly generated by polarization induction.Based on the measurement results,the average polarization intensity change rates of the composition graded In Ga N and Al Ga N are calculated,which are-0.12151 C/m²and-0.11623 C/m²,respectively,which are in line with the theoretical calculation values.To our knowledge,this is the first time to achieve polarization induced n-type doping of nitrogen polar In Ga N films.3.Study on the polarization-induced p-type doping of compositionally graded nitride films.Metal-polar Al_xGa_1-xN with decreasing Al composition（x=0.36→0.2）prepared by metal organic chemical vapor deposition（MOCVD）,realizing the polarization-induced n-type doping.At room temperature,the hole concentrations are1.0×10¹⁸cm^-3.The hole concentration changed little with temperature ranging from90 K to 300 K,indicating that the holes were mainly generated by polarization induction.Based on the measurement results,the average polarization intensity change rate was 0.05160 C/m²and lower than the theoretical value of 0.10047 C/m².We attributed it to the perspective of background electronic compensation.Moreover,for the first time we explored the doping characteristics of metal-polar compositionally graded quaternary In Al Ga N films,obtained p-type In Al Ga N films with a hole concentration of 7.3×10¹⁶cm^-3at room temperature,and analyzed the doping mechanism of quaternary graded materials.