Research On Characteristics Of Thin Barrier AlGaN/GaN Fluorine Plasma Treatment HEMT

AlGaN/GaN heterojunction is the main structure of the GaN high electron mobility transistors(HEMT). As the GaN device, it is based on the AlGaN/GaN heterojunction materials. Because of the properties of high transconductance?high saturation current and high cut-off frequency, it has a promising development on high-power microwave area. Enhancement-mode GaN HEMT has also attracted huge attention due to their broad application prospect in switching and digital field. Research on characteristics of thin barrier AlGaN/GaN HEMT with fluorine plasma treatment are carried out in this paper.Firstly, the effect of device parameters of AlGaN/GaN HEMT on the characteristics is studied with Silvaco TACD. It is found that the thinner barrier and the smaller Al component could increase threshold voltage. Plasma injection process is simulated with fluorine implanted into the AlGaN layer under the gate. Enhanced-mode device is achieved by controlling the power of injection process. With the simulation of current collapse, it is concluded that the drain current of fluorine plasma treatment HEMT reduced by 7.8%. The current collapse may be caused by the new traps that are produced due to fluorine plasma injection. Breakdown of fluorine plasma treatment device is researched with the length of field plate and the thickness of passivation layer. And it is found that thinner passivation layer could improve the breakdown voltage of thin barrier fluorine plasma treatment HEMT.Secondly, thin barrier fluorine plasma treatment HEMT are fabricated, the(80W, 120s) treatment D-Mode HEMT and the(130W, 120s) treatment E-Mode HEMT are included. Keithley4200 scs sophisticated semiconductor parameter analyzer is used to measure the electrical characteristics of those HEMT. Comparing the characteristics, we found that the threshold voltage(V th) of conventional HEMT is-2.9V,(80W, 120s) treatment HEMT is-0.6V,(130W, 120s) treatment HEMT is +0.4V. Namely, fluorine plasma treatment can increase the V th and the increment become larger with the growth of plasma treatment power. Oppositely, the leakage current of fluorine plasma treatment HEMT decreased.And then, the fluorine plasma treatment HEMT are test under the electrical stress and the change of their characteristics is studied further. Under the 1000 s off-state stress, the characteristics of(80W, 120s) treatment HEMT seriously degraded, the Vth had a serious negative drift. But under the 1000 s on-state stress, the V th of conventional and Fluorine plasma treatment HEMT all didn't degrade. It may cause by the different inner electrical field under different electrical stress. The F-ions, which are implanted into the AlGaN with the(80W, 120s) treatment, may not stable enough to resist the strong electrical filed under off-state stress, thus those F-ions may travel from the under-gate area to the source and drain. With the F-ions travel out the under-gate area, the effect of depletion decreased, which result in the degeneration of the V th.Finally, the conductance measurement in the frequency is used to characterize the change of trapping effects in devices before and after the electrical stress. With the unstable F-ions traveling under the off-state stress, there may generate new traps and cause the degeneration of characteristics. The result of conductance measurement shows that the traps in AlGaN barrier increased significantly after off-state stress, in addition, the time constant of those tarps also changed. All show that the F-ions traveling can generate the new traps.