Study On The Impact Of Negative Mobility Effect On GaN-based HEMT In Terahertz Regime

With the development of modern science and technology,semiconductor has become an indispensable part of military,scientific and social life.The whole information industry is supported by products based on semiconductor technology.Meanwhile,semiconductor technology has extended from silicon and germanium as basic materials to Ga As,Si N,Si C,GaN and other different materials,and devices and products suitable for different fields by their respective properties have been manufactured.Among them,gallium nitride(GaN)has attracted extensive attention of scientific research institutions and companies all over the world by its unique material characteristics.GaN has the advantages of wide bandgap,high electron saturation drift velocity,high temperature-resistance,excellent anti-radiation,good corrosion-resistance and excellent thermal stability.Therefore,GaN-based devices possess the characteristics of high working frequency,large power capacity,high voltage resistance and low parasitic effect,which are very suitable for the manufacture of aerospace,aviation and military equipment which need high frequency,high performance and high stability of devices.At present,the working frequency of GaN devices has reached terahertz(THz),and GaN-based terahertz power devices are widely used in military fields such as millimeter wave radar.Among them,GaN-HEMT is the core of terahertz power devices,which directly determines the performance of circuit.The research of GaN-HEMT has become one of the main interests of terahertz development and it started very early in foreign countries in this field.There have already reports of relevant experiments and results in this field,and our country is also carrying out relevant research work.Based on the above research background,and with the support of the National Science and Technology Major Project and the National Natural Science Foundation of China,the GaN-based HEMT devices are deeply analyzed and studied in this treatise.The theoretical analysis and software simulation of GaN-HEMT are carried out in terms of its size,structure and velocity-field relationship.Meanwhile,the possible application of using GaN-HEMT as Terahertz oscillator and the characteristics of gate control on oscillation frequency are studied.Finally,a new GaN-HEMT device structure which can generate terahertz signal is proposed and obtained.On the basis of consulting a large number of domestic and foreign literatures and theoretical analysis,the following work has been carried out and corresponding results have been achieved.Firstly,the basic concept of terahertz technology is introduced,including the frequency range of terahertz wave and the field of terahertz technology.Subsequently,the terahertz radiation source,which is the foundation of terahertz technology,is briefly introduced.In addition,the development status and existing problems of terahertz radiation sources are further pointed out.As the third generation semiconductor material,GaN has unique advantages in high frequency and high power applications due to its unique material characteristics.Finally,by introducing the negative differential mobility in GaN HEMT devices,the possibility of using GaN HEMT as broadband terahertz radiation sources is proposed.Secondly,the structure and working principle of GaN-based HEMT device,the simulation platform used in this paper,the simulation principle,and the specific steps and processes of simulation are described,which lay a theoretical foundation for the subsequent research.Then,the influence of GaN-based HEMT device structure on high frequency characteristics is analyzed by Silvaco-Atlas,the mainstream semiconductor simulation software.In DC simulation,the influence of gate electrode length,gate electrode position and a new recessed barrier layer structure on the two modes of operation is systematically studied,which provides a theoretical guidance for the design of GaN-based HEMT devices.Next,the enhancement effect of recessed barrier layer structure on the nonlinear characteristics of GaN-based HEMT devices is studied.By reasonably designing RBL parameters,micron-sized GaN-HEMT devices can generate high oscillation frequencies,even up to the THz regime.At the same time,by using the gate electrode region as the hot electron injection region in the channel,the length of the "dead zone" can be reduced and fixed,thus stabilizing the electronic domain and improving the device performance.The enhancement of the device performance caused by the negative differential mobility effect of GaN is explained in detail and in whole.After that,the tunable frequency characteristic of gate electrodes for GaN-based HEMT devices is studied.Compared with the planar Gunn diode,whose oscillation frequency can only be tuned by changing the distance between the cathode and anode electrodes by lithography technology,the existence of the gate electrode in our device making frequency tuning possible.This single device controllable oscillator is very useful and valuable in device designs and applications.Finally,the work of this paper is summarized,and the problems to be solved for GaN-based HEMT devices are prospected,and the future research directions are put forward.