Research On GaN-based Electronic Devices With Back Barrier Structure

GaN power electronic devices have the advantages of high efficiency,small size,and low loss.In recent years,Huawei,Xiaomi and other companies have launched more than 100mobile phone fast chargers,and have achieved preliminary verification in electric vehicles,lidar,and envelope tracking,showing a wide range of application prospects.Under high temperature and pressure,the leakage of the buffer layer in GaN devices limits the application in medium and high voltage applications such as high-speed railway and smart grids.In this paper,the 25%Al composition back barrier structure,which has a better 2DEG confinement and vertical voltage withstand capability,was used for suppressing the leakage current of the buffer layer.Based on the requirements of GaN lateral power electronic devices with low on-resistance,low off-state leakage and high breakdown voltage(BV),simulation analysis of the 25%Al composition back barrier structure was carried.Furthermore,high-performance GaN high-mobility transistors(HEMTs)and Schottky barrier diodes(SBDs)were fabricated and systematically investigated.The main research achievements are shown as follows:1.The electrical characteristics of the 25%Al composition back barrier HEMT were systematically investigated at both room temperature and high temperature.The vertical breakdown test shows that the 25%Al composition back barrier structure has excellent vertical voltage withstand capability.Through one-dimensional Poisson simulation,the effects of the Al composition of back barrier layer,thickness of the barrier layer,and channel layer in back barrier structure on energy band and carrier concentration were analyzed.It was confirmed that the 25%Al composition back barrier structure has a high 2DEG sheet density and a good 2DEG confinement.The 25%Al composition back barrier HEMT was fabricated utilizing the optimized epitaxial layer structure.The HEMT exhibits a high performance of a maximum current density(I_DS,max)of 571 m A/mm(at V_GS=2 V),a low on-resistance(R_ON)of 6.4?·mm,and a high on-off current ratio of 6×10⁹.The BV of the 25%Al composition back barrier HEMT is 1900 V.By comparing electrical characteristics of the HEMT made by the structure with 10%Al composition back barrier and other two conventional structures,the HEMT with 25%Al composition back barrier has a higher I_DS,max,a lower R_ON and a greatly suppressed off-state leakage current.The improvement of2DEG confinement makes the device have a smoother C-V platform.The DIBL effect of the device is significantly suppressed,and the BV is obviously improved.The result also shows that the HEMT with 25%Al composition back barrier suffered less degradation than HEMTs made by other structures at 150?,and maintained good performance at 300?.The reliability of the HEMT with 25%Al back-barrier structure under the on-state drain stress and the off-state gate stress were also analyzed.The results show that the HEMT with 25%Al back-barrier structure suffered less degradation.It is proved that the high 2DEG confinement of the structure could ensure the stable operation of the device at high temperature,improve the BV and device reliability.2.The electrical characteristics of the 25%Al composition back barrier SBD were systematically investigated at both room temperature and high temperature.The result shows that the SBD with 25%Al composition back barrier has a lower reverse saturation current of 3.0×10^-5 m A/mm and an R_ON of 9.1?·mm.By analyzing the effects of the recess depth on the characteristics of the SBD with 25%Al composition back barrier,the turn-on voltage of the device was reduced to 0.6 V by the fully recessed anode structure,and the current density was increased by 5 times.The characteristic degradation was significantly suppressed at 150?than that of SBD made by conventional.The reliability of the SBD with25%Al back-barrier structure under the forward current stress and the reverse voltage stress were also analyzed.The results show that the SBD with 25%Al back-barrier structure suffered less degradation.3.The interface state traps of the four materials are characterized by frequency-dependent capacitances measurement.The slow trap energy levels of the 25%Al back barrier structure at room and high temperature are 0.388?0.441 e V and 0.626?0.730 e V,and the maximum trap state densities are 1.46×10¹³ cm^-2e V^-1 and 1.11×10¹³ cm^-2e V^-1 respectively.Compared with the 10%Al composition back barrier and two conventional structures,the trap energy level is deeper and the trap state density is lower,which is one of the reasons why the gate leakage of the 25%Al back barrier structure is smaller than others.