Experimental study of the orientation effect of GaAs MESFETs fabricated on (100), (011), and (111)Ga, and (111)As substrates

An investigation of GaAs MESFETs fabricated on (100)-, (011)-, and (111)-Ga, and (111)-As substrates is discussed. An electron mobility of 4600 cm²/Vs in the Si⁺-implanted n-layer was obtained from Hall measurements with no distinct difference in results observed for the different substrate orientations. WSi_x-gate self-aligned MESFETs in all the orientations used in the experiment were fabricated. A difference in the gate-length dependence of FET parameters, especially at gate lengths shorter than 2 μm, was observed. FETs fabricated on (011) substrates had a much smaller dependence of threshold voltage shift on the dielectric overlayer thickness and gate orientation than FETs fabricated on (100) substrates. The threshold voltage shift of FETs fabricated on (111)-cut GaAs substrates depends on the dielectric overlayer thickness and the atomic plane of the substrate on which the devices are fabricated. Gate orientation did not affect FET characteristics much on (111)-cut substrates. This is explained in terms of the piezoelectric effect in a GaAs crystal. The findings indicate that (011)- and/or (111)-cut substrates are useful in fabricating high-speed GaAs ICs. They allow flexible FET layout and are free from the gate-orientation effect