Research On Structural Design And Switching Characteristics Of GaN-based Power Devices

As a typical representative of the third generation semiconductor materials,GaN has been widely concerned because of its excellent characteristics such as large band gap,high carrier mobility,and high saturation electron velocity.GaN-based heterojunction field effect transistor?GaN HFET?is one of the most widely used GaN-based power devices,with excellent frequency characteristics,power characteristics and breakdown characteristics.In recent years,researchers have continuously proposed new technologies for GaN power devices,which have made the development and application of GaN HFET devices increasingly mature.However,there are still some unresolved problems in the development of GaN HFETs.This paper focuses on the realization of enhanced devices and the improvement of device switching characteristics,etc.,in-depth research on new structural devices and device switching characteristics.In order to solve the problem of implementing enhanced devices,this article innovatively proposes an N-polar GaN HFET device structure with a composite barrier layer,replacing the barrier layer material under the gate with AlN and the composite structure of AlGaN and GaN,The polarization intensity and the two-dimensional electron gas density of the channel under the gate are reduced,thereby realizing enhanced characteristics.Compared with the conventional N-polar structure device,the threshold voltage is increased from-1.4 V to 1.3 V,and the on-resistance of the device is as low as 11.7?·mm,which is not much different from the conventional N-polar device,and the peak transconductance increased from 66 mS/mm to 103 mS/mm.Under the same overdrive voltage(V_GT=V_GS-V_th=1 V),the saturation drain current has increased from 65 mA/mm to 98 mA/mm,an increase of 51%.The simulation results show that the composite barrier layer N-polar GaN HFET device achieves a high forward threshold voltage while maintaining other characteristics without degradation,and avoids etch damage or device stability issues.In order to deeply study the influencing factors of the switching characteristics of GaN HFET devices,this paper firstly studied the impact of off-state stress on the dynamic characteristics of the device through pulse test and dynamic on-resistance test.As a result,the dynamic on-resistance increases.After the pulse signal duty cycle decreases from 50%to 1%,the dynamic on-resistance increases from 9.76??mm to10.70??mm.Secondly,through the simulation method using device-circuit hybrid simulation,the analysis shows that The turn-on time and turn-off time of the N-polar CBL GaN HFET are 7.3 ns and 40.1 ns,respectively,while the turn-on time and turn-off time of the p-type gate device are 1.6 ns and 28.4 ns,respectively.After the introduction of the gate field plate structure,the turn-on time and turn-off time of the p-type gate device increased by 12.5%and 66.2%respectively due to the increase in input capacitance and output capacitance.Finally,the simulation results indicate that the on-resistance and parasitic capacitance are the main factors that affect the switching characteristics.