Short-channel effects in sub-100 nm GaAs MESFETs

GaAs MESFETs with gate lengths ranging from 260 nm down to 30 nm have been fabricated using high resolution electron-beam lithography. The DC characteristics including transconductance, output conductance, threshold voltage, and subthreshold current of these devices have been measured. Short-channel effects manifested as a negative shift in threshold voltage and an increase in output conductance have been observed as the gate length decreased. These effects become pronounced as the device aspect ratio (gate-length/channel thickness) falls below 5. Subthreshold current increased with a decrease in gate length and is actually an exponential function of the gate bias for gate dimensions below 100 nm. Also, subthreshold current is an increasingly more sensitive function of the drain-to-source voltage as the gate-length is reduced. The observed effects are attributed to the space charge limited electron injection into the GaAs buffer layer under the channel.