| Thanks to Ga N compound semiconductors' s superior properties such as the wide bandgap,high saturation speed and high breakdown field,Al Ga N/Ga N high electron mobility transistors(HEMTs)show great potential for microwave power amplifiers and high voltage switching circuits applications.Due to the power switch and high-speed circuit driving,enhancement-mode(E-mode)Al Ga N/Ga N HEMT devices have become a hot research topic.In general,several approaches have been proposed to achieve E-mode HEMT device,including recessed gate,ultra-thin barrier designs,fluorine plasma ion implantation,p-Ga N gate and so on.Among them,F plasma treatment has the advantages of small etching damage,large positive threshold voltage shift,and small gate leakage current,which is an ideal method to fabricate E-mode Al Ga N/Ga N HEMTs.Reliability is a major problem for depletion-mode and E-mode HEMTs,especially for E-mode HEMTs.In certain application environments,the stability of F-ions in a barrier layer may cause serious reliability problems.In this paper,I conducted an in-depth study of the electrical stress reliability of the E-mode Al Ga N/Ga N HEMT device by F ion implantation.Firstly,the F ion implantation was simulated by SRIM software.The distribution of F ions in the composite target material Al Ga N/Ga N can be observed,the standard deviation parameters of its projection range can be extracted,and then the E-mode device simulation can be realized by Silvaco TCAD software.It is found that acceptor doping can tend to get close to actual results.During simulation,it can be observed that the larger the F plasma RF power is,the longer the processing time is,and the larger the threshold voltage of the device is,the easier it is to realize the E-mode.Then the F ion implanted lateral field effect rectifier is simulated,which is compatible with the F ion implanted E-mode device.Next,the F ion implantation is simulated to realize the E-mode MIS-HEMT device,and effects of gate dielectric thickness and F plasma treatment condition on device characteristics are studied.Finally,according to the two popular degradation mechanisms of F plasma implantation,the electrical stress simulation was performed.The results are consistent with the degradation trends under each stress condition.Secondly,the influence of on-state stress,off-state stress and drain step stress on F plasma treated Al Ga N/Ga N HEMT were investigated respectively,and the reliability of the device under the electrical stress after F plasma treatment was studied.Under on-state stress,the hot electrons in the channel may inject into the Al Ga N barrier layer against the barrier height,and parts of the F ions are ionized,resulting in a negative shift of the threshold voltage,and the hot electrons may also be trapped by the defects or interface traps in gate-drain region,which leads to a virtual gate effect.Under the off-state stress,due to the fact that the Schottky characteristics of the device are not significantly degraded,the ionization of F ions induced by the gate electron injection is not taken into consideration.It is believed that F ions undergo electro-migration under the off-state electrical field,which weakens the F ion depleting the 2DEG in the channel and causes degradation of device performance.Under the drain step off-state stress,E-mode device shows significant degradation,while the Schottky characteristics of the device is not degraded.Therefore,the degradation of the electrical characteristic of the device is attributed to the electro-migration of the unstable F ions under the off-state electric field,which leads to the redistribution of the electric field and eventually to a new equilibrium.Finally,according to the reliability problem of the studied electrical stress,two measures are proposed to improve the reliability of the E-mode device the F ion implantation,namely the dual-gate or source-field plate structure and the p-Ga N buried in buffer layer structure. |
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