Effects Of Electrical Stress And Hydrogen Effect On GaAs PHEMT Devices

Gallium arsenide(GaAs)is widely used in microwave applications due to its high electron mobility and high electron saturation velocity.Among GaAs devices,pseudomorphic high electron mobility transistor(PHEMT)is recognized as one of the most promising high-speed electronic devices in the microwave and millimeter wave fields.With the massive use of GaAs PHEMT,the reliability of which has attracted extensive attention.This work is an in-depth study on the degradation of GaAs PHEMT under electrical stress and under hydrogen effect.Both electrical characteristics and low-frequency noise characteristics are extracted to investigate the degradation mechanism of the devices under such conditions.The main work of the research includes:(1)Degradation of GaAs PHEMT under both off-state and open-state electric stresses is studied.Experimental results show that after off-state electric stress,decrease in off-state leakage current,peak transconductance,and saturated drain current can be observed.However,in the state of on-state stress,an increase in off-state leakage current can be recognized,while other characteristics still fall.Furthermore,the greater the applied electric stress,the more significant the degradation.Based on these results,an explanation of the degradation of GaAs PHEMT is presented.(2)The effect of hydrogen on GaAs PHEMT performance is discussed.Device characteristics before and after hydrogen treatment is obtained and compared in this section.It can be found that after hydrogen treatment,off-state leakage current increases slightly while peak transconductance and saturated drain current would fall.Besides,increase in bothflat band voltage power spectral density Svfband Density of trap states Nt can be found after hydrogen treatment,especially for N_t,an increase from 8.35×10¹²cm^-3eV^-1 to1.21×10¹³cm^-3eV^-1 occurs.After that,in order to exclude the effect of environment temperature,device performance in N₂ atmosphere under 120?is tested,which in turn suggests no notable effect would occur after high-temperature treatment only.The main reason is that atomic hydrogen penetrates into the interface between the gate metal and the semiconductor and the barrier layer,thereby increasing the density of trap states in the device.(3)Device reliability under off-state bias after hydrogen and high-temperature treatment is investigated.The results show that there is no significant change in the electrical properties of the device under off-state stress only.However,these characteristics change slightly under off-state stress after high-temperature treatment.Besides,decrease in off-state leakage current,peak transconductance,as well as saturated drain current can be observed in hydrogen-treated devices under off-state electric stress.Additionally,Nt increases from1.21×10¹³cm^-3eV^-1 to 1.02×10¹⁴cm^-3eV^-1 as S_vfb also rises.Based on the experimental results above,it can be concluded that device reliability under electric stress would degrade after hydrogen treatment.Hydrogen atoms diffused into the metal-semiconductor interface and barrier can raise the trap density inside the device,leading to a self-built electric potential at the metal-semiconductor interface.The main reason is that under a high field,further diffusion of hydrogen atoms into the channel region further increases the density of trap states in the device,leading to further deterioration of device performance.