Effects of tensile stress induced by silicon nitride passivation on electrical characteristics of AlGaN∕GaN heterostructure field-effect transistors

The effects of tensile stress induced by silicon nitride (Si3N4) passivation on electrical characteristics of AlGaN∕GaN heterostructure field-effect transistors (HFETs) were investigated. The biaxial tensile stress applied to the AlGaN layer was increased with the thickness of the Si3N4 passivation layer, leading to the increase of sheet charge density confined at the heterointerface. The stress-induced charge density was 1.75×1011e∕cm2 for 80-nm-thick Si3N4 and 6.74×1011e∕cm2 for 500-nm-thick Si3N4. The maximum drain current and transconductance of AlGaN∕GaN HFET increased from 769 to 858mA∕mm and from 146 to 155mS∕mm after passivation, respectively.