Observation of high field regions in GaAs MESFETs by using Kelvin probe force microscopy

We have succeeded in measuring potential profile of GaAs MESFETs by using Kelvin probe force microscopy and compared it with that of AlGaAs/InGaAs PHEMT (x/sub ln/=0.2). The obtained potential profile was different from that of PHEMT. Two-dimensional (2D) device simulation taking the surface state into account revealed that the surface states relaxed the high field at the gate edge. The high field at drain edge was also measured on ungated FETs and was explained by taking both the electron-velocity saturation and surface states.