Research On Normally-off AlGaN/GaN HEMT Device

Semiconductor technology has developed rapidly in recent years.Traditional semiconductors devices have almost reached the limit.The new third-generation wide bandgap semiconductor such as Ga N and Al Ga N have become the hotspots.Ga N has good physical,chemical and electrical properties and performances in fabricating high-frequency,high-temperature and high-power devices.Among them,Al Ga N/Ga N HEMT devices perform the most outstanding.However,the current research results mainly focus on the normally-open devices.Hovewer,the normally-off devices are required in the high-speed switching,RFIC,digital circuits field.So the research of normally-off Al Ga N/Ga N HEMT devices has very realistic significance and value.First of all,a large number of literatures are reviewed and the characteristics of Ga N semiconductor materials are briefly introduced.The structure characteristics and working principle of HEMT devices and the methods to achieve normally-off devices are described in detail in this thesis.Then the Silvaco TCAD software is introduced,including numerical calculation,the main components and methods of use,the physical basis of semiconductor simulation and the basic model of device simulation.Then,a new type of normally-off Al Ga N/Ga N HEMT device is designed baesd on the structure of trench gate etching.Due to the polarization,the Al Ga N/Ga N heterojunction interface has a high concentration of two-dimensional electron gas,so the device is normally open in nature.A layer of Si₃N₄ dielectric layer is added into the barrier layer in this device to make the 2DEG that generated by polarization become discontinuous.So the device becomes a normally-off type.The device is simulated by silvaco TCAD.The influence of each parameter on the device performance is analyzed,including the Al composition concentration,the barrier layer thickness,medium length,gate dielectric layer thickness,etc.The most appropriate values of each parameter are determined from the simulation results.The Al Ga N barrier layer is divided into two parts,the thickness of the first part is 15 nm,the Al composition is 0.3,the thickness of the second part is 1nm,the Al composition is 0.05.The gate length?Lg?is 3?m,the gate width?Wg?is 100 ?m,the gap between the gate and the source?Lgs?is2.5?m and the gap between the gate and the drain?Lgd?is 3.5?m.The threshold voltage is 1V,and when Vds = 10 V,the peak transconductance of the device is45 m S/mm?Wg = 0.1mm,Vgs = +3V?.When the gate voltage is +10 V,the current is 50 m A and the saturation current density is 500 m A/mm?Wg = 0.1 mm?,the characteristic on-resistance is2m?·cm2.Finally,multi-media normally-off devices are designed on the basis of the new type ofnormally-off device stucture in this thesis and conduct a simulation analysis.Compared with the normally-open device without the dielectric layer,the threshold voltage of the normally-off device that designed in this thesis is forward-shifted by 1.6V.The design of the structure is flexible,the structure of the device can be preset in material design,so that the influence of the device design can be extended to the material growth stage.In the production process,the damage caused by trench gate etching is avoided in this device after the optimization of barrier layer.The problem of accurately controlling the depth of etching is solved and the production cost is reduced.