Current collapse reduction in InAlGaN/GaN high electron mobility transistors by surface treatment of thermally stable ultrathin in situ SiN passivation

• 5 nm In situ SiN passivation for InAlGaN/GaN high electron mobility transistors.
• No device degradation after operation at 600 °C.
• Charge trapping related to partial surface oxidation of the passivation.
• Surface cleaning by Ar sputtering strongly decreases current collapse.

The impact of surface treatment of 5 nm in situ SiN passivation on the performance of InAlGaN/GaN high electron mobility transistors is analyzed. After operation at 600 °C, no device degradation is observed, confirming the thermal stability of the passivation layer. The in situ SiN, grown by metalorganic chemical vapor deposition, is treated by first Ar ion sputter cleaning, intentional oxidation in water and second cleaning. The results of current collapse characterization show that the SiN surface contains a humidity related trap density of about 1.04 × 1012 cm−2, which can be reduced to 0.21 × 1012 cm−2 by Ar sputter cleaning. The surface cleaning allows for deposition of further layers without degradation of the device properties. In this study, 25 nm SiN is deposited subsequently by conventional plasma enhanced chemical vapor deposition, resulting in the same device performance as the devices processed with 30 nm in situ SiN.