Comparison of the orientation effect of SiO 2 - and Si 3 N 4 -encapsulated GaAs MESFET's

This letter compares the influence of stressed-SiO 2 and Si 3 N 4 films on threshold voltage of WSi x -gate self-aligned GaAs MESFET's oriented along [011]- and [011]-directions. The experimental results showed that the orientation effect originates, mainly from piezoelectric effect due to strain in the n-layers, induced by the dielectric overlayer. Furthermore, the disagreement among workers regarding the preferable orientation turned out to be due to the difference of the stress-sign in dielectric overlayers employed; it was confirmed that SiO 2 film is in compressive stress and Si 3 n 4 film in tensile stress on GaAs.