Vth control in GaAs by substrate parameters

We have investigated the variation of threshold voltage (Vth) with regard to the resistivity (p) of the semi-insulating substrate, and have found that there is a good correlation between p and Vth. It has previously been reported that the uniformity of Vth (/spl sigma/Vth) has a relation to the uniformity of microscopic resistivity (/spl sigma/p/p) of the semi-insulating substrate. We have studied a correlation between /spl sigma/p/p and the Hall mobility of the semi-insulating substrate (/spl mu//sub H/). It has been found that a substrate with a higher /spl mu//sub H/ can produce better /spl sigma/Vth. These results suggest that the Vth can be controlled by substrate parameters such as resistivity and mobility.