Study On AlGaN/GaN/AlGaN Double Heterojunction HEMT Devices And Characteristics

Due to the excellent properties of GaN-based materials such as wide band gap,high saturation electron velocity and high breakdown field strength,AlGaN/GaN high electron mobility transistor has received extensive attention and rapid development.In recent years,the performances of conventional AlGaN/GaN heterostructure materials and devices have obtained great improvement with the progress of the material quality and device technology stability,especially in terms of high frequency and high power characteristics.Meanwhile,more advanced device structures are being explored for further performance improvement,for example,the double channel heterojunction HEMTs are one of these structures.The double heterostructure improves the device characteristics by improving the confinement of the two-dimensional electron gas,which can effectively alleviate the current collapse effect,improve the breakdown characteristics,and improve the reliability of the device.This thesis studies from device simulation,material characterization and device preparation and testing.The main work contents are as follows:Firstly,the simulation of the double heterojunction and graded aluminum component barrier layer structure device was studied.The results show that the AlGaN buffer layer can improve the carrier's confinement and enhance with the increase of Al composition,but at the same time reduce the carrier concentration,and finally determine the Al composition is 0.05.the graded aluminum component barrier layer structure can enhance the current density while uniform the electric field intensity distribution and increase the breakdown voltage of the device.Secondly,the surface morphology and electrical properties of AlGaN/GaN/AlGaN double heterojunction materials were characterized.The surface roughness RMS of the material measured by AFM was 0.464 nm.The XRD results show that the half height width of the(002)and(102)planes were 227 arsec and 350 arsec respectively and the corresponding screw dislocation density and edge dislocation density were respectively 1.038×108cm-2 and 6.617×108cm-2.The room temperature non-contact Hall test show that 2DEG mobility and area densities of 1821 cm2/Vs and 1.3E13 cm-2 respectively,and the sheet resistance of the material was 264 ?/sq.Finally,AlGaN/GaN/AlGaN double heteroj unction HEMT devices were fabricated and their electrical properties and reliability were tested and characterized.The results show that as the gate-drain spacing increases,the maximum saturation current and transconductance of the device decrease,and the breakdown voltage increases.Compared with the conventional single heterojunction,the double heterojunction device can increase the breakdown voltage from 120 V up to 200V,and can effectively improve the current collapse effect of the device.As the temperature increases,the material sheet resistance increases,the device off-state leakage current and the Schottky forward and reverse current increase,and the saturation current density and transconductance decrease.The frequency characteristic fT/fmax of the double heterojunction device is 50 GHz/75 GHz.The power characteristic test shows that as the drain voltage increases,the saturation power density and gain increase,and the power added efficiency decreases.