The Characteristical Simulation And Structural Optimization Of TRG-GaN HEMTs High Linearity Devices

The semiconductor materials with wide band gap such as GaN has demonstrated excellent performance in microwave and high power applications,and have increasingly become the focus for many researchers.In the past few decades,thanks to the advantages of the wide band gap and high electron saturation speed of GaN materials,the application of high electron mobility transistors based on AlGaN/GaN heterojunction has made great progress.However,in the application of power amplifiers,the nonlinearity is still one of the difficulties,which hinder in the way.In particular,the linearity of GaN-based power amplifiers is an important standard for evaluating the wireless transmission systems.It is a basic requirement for high linearity devices to maintain the peak of transconductance in a large voltage range.The Transitional-Recessed-Gate(TRG)technology,which combines the advantages of adjusting barrier thickness and the recessed gate to improve the linearity,has brought new ideas for the design of high linearity devices.Firstly,this article introduces the basic working mechanism of AlGaN/GaN HEMTs devices and the essential concepts of high linearity devices,then uses the current formula to analyze qualitatively the resources of the nonlinearity for GaN HEMTs devices,and finds two key factors which determine the flatness of the device's transconductance(mobility and twodimensional electron gas concentration),at last,we discusses the common measures applied in the design of HEMT high linearity devices recently,coming up with the TRG technology.As a new method,it is possible to adjust the flatness of transconductance for using the TRG technology.However,due to the constraints of technology,the TRG technology is not mature under the current conditions of process,so we try to use the simulation to do the research.Silvaco is applied to simulate the basic structure of GaN HEMTs with TRG technology.Considering the material and special structure of the device,the suitable polarization charge model and mobility model should be selected.Because of the different thickness and the electric field under the gate,GANSAT model,a high-field model which is related to the electric field is introduced,and the relevant model parameters are matched according to the experimental values with different barrier layer thickness.After the set of the model,the two-dimensional DC characteristics of AlGaN/GaN HEMTs devices with TRG technology applied in the gate length direction are simulated,and the related electrical characteristics of the conventional type devices are also simulated for comparison.The third-order intermodulation distortion in the device is related to the higher-order derivatives of transconductance,so the transconductance curve of the device should be made to further study.Subsequently,we study the transitional type,the gradient of transitional structure,the barrier layer thickness and the gate length of the transitional-recessed-gate applied in the length direction.We make a conclusion that the symmetric transitional-recessed-gate structure,when the gradient is small,the thickness of the barrier layer is large and the length of the gate takes an intermediate value,the device will obtain the best flatness for transconductance.But the barrier layer can not be very thick,it will cause the loss of the peak value of the transconductance,so the thickness of the barrier layer should be adjusted according to the requirements.At the end of this paper,the three-dimensional simulation of the GaN-based HEMT device with a transitional-recessed-gate applied in the gate width direction is completed,and the transfer characteristics and transconductance curves of the conventional device are simulated for comparison.As the characteristics of the device are not sensitive to the varied model parameters when recessed depth changes,the simulation results of the three-dimensional device do not meet expectation.It is undeniable that TRG technology is a new way to solve the nonlinear problem for device,and it still has positive significance in future research.