Design And Fabrication Of GaN Based Gate Recessed MOSFET Devices

AlGaN/GaN heterojunction due to the polarization effect in the heterojunction interface near the GaN side produced a two-dimensional electron gas channel with high concentration and high electron mobility,which makes the AlGaN/GaN HEMT devices have small conduction resistance,fast switching speed,large forward conduction saturation current density,thus obtained wide attention and research.However,the conventional HEMT devices are normally on devices,the devices need negative pressure drive in practical application,which make driving circuit designing more difficulty and cost increasing,and the negative pressure driving circuit without failure protection function,make the system less secure.Therefore,how to achieve high performance enhanced GaN power electronic devices has become a hot research topic.In this paper,the GaN device is realized by the structure of the gate recessed MOSFET device.The enhancement mechanism of gate recessed MOSFET is to weaken the polarization effect of gate heterojunction by changing the gate below the barrier layer thickness,which deplete the two-dimensional electron gas in gate recessed bottom channel,complete threshold voltage regulation,in order to achieve enhanced device.In this paper,the influence of the depth of T on the threshold voltage of the device is studied by simulation software.Based on the theoretical analysis of the simulation,the experimental investigation of the AlGaN/GaN gate recessed MOSFET devices is carried out.In the experiment,the abnormal phenomenon of the threshold voltage of the gate recessed MOSFET device is negative.The C-V characteristics of the test device show that there are a lot of fixed positive charges in the interface between Al₂O₃ and GaN.Though the Ab into study,the positive charge is generated due to the dangling bonds gate recessed etching to produce a large number of Ga bond,and the binding energy of Ga-O bond is less than Ga-N,in gate dielectric Al₂O₃ the atoms O to replace N atom in the formation of Ga-O bonds,Ga-O bonds and dangling bonds of Ga are significantly positive characteristics.The fixed positive charge attracts the same amount of electrons at the bottom of the grid,so that the threshold voltage of the gate recessed device is negative.In order to reduce the charge density of positive charge in the gate dielectric Al₂O₃ and GaN interface,the post gate dielectric annealing in N2 atmosphere process was introduced in experiment.N ion Al₂O₃/GaN interface heat treatment can effectively restore the Ga-N bond,reduce the positive charge density of Al₂O₃ and GaN,and achieve a wide range of threshold voltage modulation of 7.1V.Reducing the concentration of the interface positive charge can weaken the channel scattering mechanism,increase the channel mobility,finaly recesive the E-mode device with VTH=7.6V,Ron=19.5?.mm,Idmax=355mA/mm,BV=1050V@Lgd=20?m.These values are the highest reported for E-mode GaN devices with VTH>5V at present.