Improved Threshold Voltage Uniformity in GaAs MESFET Using High Purity MOCVD-Grown Buffer Layer as a Substrate for Ion Implantation

High purity and high resistivity MOCVD-grown GaAs layer was found to be a very suitable substrate for the fabrication of MESFET by direct ion implantation. Such a substrate (MO-substrate) has been grown using a low pressure MOCVD system by adjusting the [AsH3]/[TMG] ratio. MESFET's were fabricated using a W–Al gate self-alignment process, and V th scattering was compared between the MO-substrate and an undoped LEC substrate. Extremely small V th standard deviation of 18.5 mV was obtained in a 2-inch full wafer of MO-substrate at a mean value of +220 mV.