Research On Current Collapse Effect Of New Field Plate Structure GaN HEMT

Due to its excellent performance such as wide band gap,strong breakdown electric field,high electron saturation drift speed,GaN HEMT has been widely used in wireless communication,radar,microwave and other fields.But current collapse is still one of the main factors limiting the large-scale application of devices.The basic characteristics and current collapse of AlGaN/GaN HEMT are studied.Two kinds of device structures are proposed to improve current collapse.The main work of the thesis is as follows:1.The research status and existing problems of AlGaN/GaN HEMT devices are summarized.The basic structure and working mechanism of AlGaN/GaN HEMT are analyzed.The output characteristics,transfer characteristics and transconductance characteristics of the device are studied.The polarization effect and the mechanism of 2DEG in AlGaN/GaN heterojunction are analyzed.The factors affecting 2DEG are analyzed,including AlGaN barrier layer thickness,barrier layer Al composition.2.Based on the double pulses technique,the current collapse of AlGaN/GaN HEMT is studied.The channel electrons are trapped by the buffer trap under the peak electric field.Because the response speed of the trap in the buffer layer is slow,the output current cannot directly reach the steady state value,which leads the current collapse.The new structure is proposed by introducing a grooved field plate AlGaN/GaN HEMT.This structure reduces the peak electric field and introduces a uniform electric field distribution by introducing a grooved field plate at the edge of the gate.Comparing with the conventional structure,the current collapse amount of this new structure is reduced from 13.6%to 3.3%.Structural parameter row is optimized and analyzed.Field plate length Lfp is 1μm,thickness of the passivation layer under the field plate H+Hfp is 15nm.3.The grooved field plate structure reduces the output current of the device drain while improving current collapse.The new structure is proposed by introducing a grooved double field field plate structure.In this new structure,a vertical electric field line parallel to the bottom of the gate will be generated directly under the dual field plate,which reduces the electric field lines at the gate edge and the edge of the field plate FP1.Therefore,the parameter design of the groove structure is more free.Comparing with the groove field plate structure,the thickness of the barrier layer increases,the channel electron concentration increases,and the output leakage current increases.The grooved double field plate structure will not reduce the drain output current when improving the current collapse.Comparing with the conventional structure,the current collapse amount of the new structure is reduced from 13.6%to 0.8%.The groove and field structures in the new structure optimized.The optimized parameter values are given.4.In the new structure device,the effect of different buffer layer trap concentrations on current collapse is analyzed.As the trap concentration of the buffer layer increases,the amount of current collapse decreases.The reason is that the larger the trap concentration of the buffer layer,the deeper the potential well on the GaN side,and the electric filed peak is reduced by the field plate structure,which leads channel electrons to be difficult to be captured by the buffer layer trap.Therefore,the higher the buffer trap concentration,the more significant the improvement of the current collapse in the new structure device.