Study of Surface Passivation with Different a-SiN_x: H Films Effect on AlGaN/GaN HEMTs

摘要

The effects of surface passivation with different a-SiN_x: H films on AlGaN/GaN high-electron-mobility transistors (HEMTs) have been investigated. The surface passivation layer of a-SiN_x:H is deposited by plasma enhanced chemical vapor deposition (PECVD) using a 13.56 MHz direct plasma system and a S1H_4/NH_3 / N_2 gas mixture. The current-voltage and gate-drain diode characteristics of AlGaN/GaN HEMTs before and after passivation using different PECVD recipes are analyzed. The drain current increases and the threshold voltage shifts to negative values after passivation, because surface passivation reduces the surface state density and so increases the sheet carrier density. We have also analyzed the role of the [N]/[Si]-ratio x and H atom content of a-SiNx :H films on the passivation properties. Silicon-rich a-SiNx :H film with refractive index of 2.01 and large Si-H content contains less K+ centers and has high-quality surface passivation. The possible mechanisms by which a surface passivant prevents current collapse are discussed.