Numerical analysis of impact of stress in passivation films on electrical properties in AlGaN/GaN heterostructures

The impact of forces due to the difference in mechanical stresses between the Schottky contacts and passivation films on the electrical properties of (0001) AlGaN/GaN Schottky diodes is numerically analyzed in the framework of the edge force model. The compressive (tensile) passivation films induce negative (positive) piezoelectric charges below the Schottky contacts in the GaN channels and bring forth onsets of the concentration of two-dimensional electron gas at shallower (deeper) bias voltages. The change in the bias voltages at the onset due to edge forces of +/- 0.5 GPa . mu m is 1 or 2V for diodes with 0.5-mu m Schottky contacts. This indicates that passivation films with the designed stress play a crucial role in controlling the threshold voltages of AlGaN/GaN HEMTs.