Improvement of Vthcontrol for GaAs FET's by shallow-channel ion implantation

Fluctation of a net electrical activity of implanted impurities is thought to be the main origin of fluctuation of the threshold voltage (V
th
) of GaAs FET's which have a channel layer formed by ion implantation directly into semi-insulating substrates. Net electrical activity is affected by several factors such as implantation damage and the nature of the substrate. Calculation of V
th
predicts that a shallow channel is advantageous to reduce the fluctuation of V
th
when the fluctuation of the net activity of implantated impurities predominates in that of V
th
. The advantage of the shallow channel was verified experimentally by a through-film implantation technique, which was one of the ways to realize the shallow-channel FET.