Interface Defect Hydrogen Depassivation and Capacitance-Voltage Hysteresis of Al₂O₃/InGaAs Gate Stacks

We investigate the effects of pre- and postatomic layer deposition (ALD) defect passivation with hydrogen on the trap density and reliability of Al₂O₃/InGaAs gate stacks. Reliability is characterized by capacitance-voltage hysteresis measurements on samples prepared using different fabrication procedures and having different initial trap densities. Despite its beneficial capability to passivate both interface and border traps, a final forming gas (H₂/N₂) anneal (FGA) step is correlated with a significant hysteresis. This appears to be caused by hydrogen depassivation of defects in the gate stack under bias stress, supported by the observed bias stress-induced increase of interface trap density, and strong hydrogen isotope effects on the measured hysteresis. On the other hand, intentional air exposure of the InGaAs surface prior to Al₂O₃ ALD increases the initial interface trap density (D_it) but considerably lowers the hysteresis.