Investigation Into GaAs Power MESFET Surface Degradation

Long term degradation of GaAs power MESFETs is shown to be surface-induced. - C.V.D. SiO2 protected FETs are investigated in part 1 : using micro-Auger analysis (beam spot size ¿0.1 - 0.2 ¿m), we have identified a Gallium outdiffusion induced by the SiO2 surface protection deposition and a GaAs oxidation mechanism during electrical operation. These reactions modify the electrical surface properties in the access regions explaining the R.F. and D.C. performances degradation. This part I constitutes the body of this communication. - part II : After a review of our results on unprotected FETs, a plasma enhanced chemical vapor deposited silicon nitride layer is shown to be a suitable passivation.