Study Of Two-dimensional Electron Gas Transport Properties In GaN High Electron Mobility Transistors

With the emergence and rapid development of high-frequency communication,electric vehicles and new-energy technologies,various industries have imposed increasingly high requirements on the performance of semiconductor materials and devices.The first and second generation semiconductor materials represented by Si and GaAs have gradually failed to meet the needs of modern information technology development due to the limitation of their own material performance.Recently,with the development of semiconductor technology,the research,development and production of the third generation of wide-bandgap semiconductor materials and devices represented by gallium nitride(GaN)gradually began to mature,and its excellent physical and chemical properties give GaN-based devices better high-frequency and high-voltage characteristics and stability.Wurtzite GaN has strong polarity itself,and due to the difference between spontaneous polarization and piezoelectric polarization,a high density of polarization charge is generated at the AlGaN/GaN heterojunction interface.The positively charged polarization charges in turn induce a high density of twodimensional electron gas(2DEG)near the heterojunction interface.Due to the absence of doping,the 2DEG in GaN high electron mobility transistors(HEMTs)has a high mobility,which makes GaN HEMTs have excellent high-frequency characteristics and short response time.Inorder to further improve the performance of GaN HEMTs,it is necessary to reduce the scattering of 2DEG inside the devices through advanced device processes and device designs,and thus increase the carrier mobility.Therefore,the study of 2DEG transport properties in GaN HEMTs is extremely important.The main research of this thesis is as follows:1.The physical mechanism of introducing GaN interlayer to improve the mobility of 2DEG in InAlN/AlN/GaN/InGaN/GaN HEMTs was investigated.The results show that the introduction of the GaN interlayer significantly changes the distribution of2 DEG in the first two subbands as well as the mobility.As the thickness of the GaN interlayer increases from 1 nm to 6 nm,2DEG suffers significantly less alloy disorder scattering in the first subband.However,the second subband still has a large number of electrons distributed in the InGaN channel region,so the mobility of 2DEG in the second subband is still mainly limited by the alloy disorder scattering.Inaddition,the polar optical phonon scattering on the first two subbands is also gradually weakened with the increase of GaN interlayer thickness.2.The mechanism by which proton irradiation degrades the performance of AlGaN/AlN/GaN HEMTs has been investigated,and the results show that the Gavacancies generated inside the device by proton irradiation cause the decrease of 2DEG density and mobility.As an acceptor-like defect,the ionized Gavacancies in the GaN channel significantly enhance the ionized impurities scattering,resulting in a significant decrease in the 2DEG mobility.3.The effect of the AlGaN back-barrier on the irradiation hardness of AlGaN/AlN/GaN HEMTs is investigated.The calculated results show that the introduction of AlGaN back-barrier degrades the irradiation hardness of GaN HEMTs.After proton irradiation at the same dose and energy,the decrease of 2DEG mobility in AlGaN/AlN/GaN/AlGaN HEMTs is more obvious compared to AlGaN/AlN/GaN HEMTs.