Noise in ungated GaAs F.E.T.

A noise study of ungated GaAs MESFET's has been made. Measurements of the equivalent noise temperature have been performed in the V.H.F. range. An original simple experimental procedure is described. From these data it is found that the Baechtold relationship : T = To[1+ δ(E/ES)³] between electron noise temperature T and electrical field E holds only roughly for small electrical fields beyond saturation. A noise variation with E³has been measured but the noise coefficient δ is in the range of 3 to 40. For larger electrical fields, noise temperature increases exponentially as a function of the voltage but saturates for higher fields. For all bias conditions noise performance may be greatly deteriorated by contact noise. It is concluded that such a noise characterization provides an accurate and easy method of selecting the best epitaxial layer for low noise FET's before gate deposition.