Research Of Dynamic Doping Effect On The Surface Of AlGaN/GaN Heterojunction

AlGaN/GaN HEMThave been widely used in high-frequency and high-power applications due to their excellent properties,including high breakdown voltage,high electron mobility,and high 2DEG concentration.The concentration of nonintentionally doped AlGaN/GaN heterojunction 2DEG can reach 1013 cm-2,but the microcosmic source of 2DEG at the bare AlGaN/GaN heterojunction interface is still a matter of debate in the academic community.Insufficient understanding of the source of 2DEG not only affects the development of device manufacturing technology but also affects the enhancement and stability of device performance,such as modulation of the threshold voltage of HEMT devices,suppression of current collapse,modulation of 2DEG concentration,detection of impurity energy levels in GaN materials,and so on.This paper studies the relationship between the molecular groups adsorbed on the GaN surface and the 2DEG at the AlGaN/GaN interface through experimental and first-principles calculations,and designs a series of experiments to demonstrate the microcosmic source of 2DEG at the AlGaN/GaN interface,proposing the "surface dynamic doping mechanism" to explain the generation and saturation of 2DEG.Using the amplification effect produced by the time integration of the surface dynamic doping mechanism,the detection of F impurity energy levels in the AlGaN barrier layer was designed and achieved based on the two-photon process.In addition to this,based on the surface dynamic doping mechanism,the response of AlGaN/GaN heterojunctions to organic gases was realized.The paper mainly consists of the following three parts:1.Study on the origin of 2DEG at the AlGaN/GaN heterojunction interface.Based on experimental and first-principles calculation,we propose the "surface dynamic doping mechanism" to explain the generation of 2DEG at the AlGaN/GaN heterojunction interface.In the experiment,the effects of different environmental,such as polar solvents,vacuum,different atmospheres,and different wavelengths of light on the concentration of 2DEG at the AlGaN/GaN heterojunction interface were verified by changing the surface enviroment of the AlGaN/GaN heterojunction.The experimental results show that when O2 molecules on the AlGaN/GaN heterojunction surface are detached due to external forces(such as vacuum pumping,polar solvent cleaning,infrared light irradiation,etc.),the concentration of 2DEG in the AlGaN/GaN heterojunction channel corresponding to it decreases.When O2 molecules are adsorbed on the AlGaN/GaN heterojunction surface under the assistance(light irradiation,high temperature,etc.)the concentration of 2DEG is increases.The adsorption and desorption of O2 molecules on the AlGaN/GaN heterojunction surface are always present,so we call it "dynamic doping" of O2 molecules on the AlGaN/GaN heterojunction surface.First-principles calculation show that the energy level of O2 molecules on the GaN surface is located 1.39 eV below the GaN CBM,and can provide electrons to the AlGaN/GaN heterojunction channel.The adsorption of O2 molecules on the AlGaN/GaN heterojunction surface does not form a chemical bond,which is consistent with the phenomenon observed in the experiment.2.Based on the amplification effect produced by the time integration of the"surface dynamic doping mechanism" of the AlGaN/GaN heterojunction,combined with the two-photon process,the detection of the position of F impurity energy levels in the AlGaN barrier layer was designed and achieved.In the experiment,CF4 plasma was injected into the AlGaN barrier layer using ICP technology,and SIMS was used to characterize the concentration distribution of F elements in the AlGaN/GaN heterojunction.In the detection of F impurities,when two complementary lights were simultaneously irradiated on the device surface and the complementary wavelengths gradually changed,a significant increase in the concentration of 2DEG at the AlGaN/GaN heterojunction interface was observed only in the complementary light corresponding to the energy level of F,allowing the energy level of F to be detected at 2.8 eV and 3.25 eV below the AlGaN CBM.3.Based on the "surface dynamic doping mechanism" of the AlGaN/GaN heterojunction,plasma treatment was used to make the heterojunction sensitive to polar gas molecules.In the experiment,CF4 plasma was injected into the AlGaN/GaN heterojunction barrier region using ICP equipment to change the coupling mode between surface molecules and internal charges of the material,reduce the detachment energy of surface molecules,and achieve the response of the AlGaN/GaN heterojunction to gas molecules such as ethanol,acetonitrile,and acetic acid.The current change of the AlGaN/GaN heterojunction for the above gases was 52%,51%,and 61%,respectively.