Effective control of active interface traps in GaN HEMT epitaxial layers by stress tuning of SiN<i> _x </i> passivation layers

Abstract This work reveals how the number of active interface trap states in an AlGaN/GaN epitaxial structure can be influenced by SiN x passivation without modifying the semiconductor/passivation interface. We compare the density of interface trap states for passivations comprising SiN x layers with different built-in compressive stresses of 46 MPa and 956 MPa. Metal–insulator–semiconductor capacitors were fabricated for electrical characterization. As the insulator we used a single and bi-layer stack of SiN x with two thicknesses—100 nm and 150 nm in total for each stack. Capacitance–voltage, capacitance–frequency and conductance–frequency measurements were performed. The extracted density of interface traps remained 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 the 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 changed from 0.198 V nm −1 for single-layer to 0.277 V nm −1 for bi-layer passivation, thus reducing the trap interaction to the two-dimensional electron gas. We propose to use this effect as an effective method to control the active interface trap states in GaN-based transistors.