Effective control of active interface traps in GaN HEMTs epitaxial layers by stress tuning of SiNx passivation layers

This work reveals how the number of active interface trap states in the AlGaN / GaN epitaxial structure can be influenced by the SiN x passivation without modifying the semiconductor / passivation interface. We compare the density of interface trap states for the passivations comprising of SiNx layers with different built-in compressive stress: 46 MPa and 956 MPa. Metal-insulator-semiconductor (MIS) capacitors were fabricated for electrical characterization. As insulator, we used a single and bi-layer stack of SiNx with two thicknesses: 100 nm and 150 nm total for each stack. Capacitance-voltage, capacitance-frequency and conductance-frequency measurements were performed. The extracted density of interface traps remains in the range from 2.6 × 10 11 cm -2 to 4.0 × 10 11 cm -2 for the structures with tested SiN x layers. These minor differences in density of states do not indicate an advantage from any SiN x passivation stack variation used in our experiment. On the other hand, the trap activation electric field changes from 0.198 V/nm for single layer to 0.277 V/nm for bi-layer passivation, thus reducing the traps interaction to the 2DEG. We propose to use this effect as an effective method to control the active interface trap states in GaN-based transistors.