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 (Vth) 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 Vthpredicts that a shallow channel is advantageous to reduce the fluctuation of Vthwhen the fluctuation of the net activity of implantated impurities predominates in that of Vth. 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.