Impact of La₂O₃ interfacial layers on InGaAs metal-oxide-semiconductor interface properties in Al₂O₃/La₂O₃/InGaAs gate stacks deposited by atomic-layer-deposition

We examine the electrical properties of atomic layer deposition (ALD) La₂O₃/InGaAs and Al₂O₃/La₂O₃/InGaAs metal-oxide-semiconductor (MOS) capacitors. It is found that the thick ALD La₂O₃/InGaAs interface provides low interface state density (D_it) with the minimum value of ∼3 × 10¹¹ cm⁻² eV⁻¹, which is attributable to the excellent La₂O₃ passivation effect for InGaAs surfaces. It is observed, on the other hand, that there are a large amount of slow traps and border traps in La₂O₃. In order to simultaneously satisfy low D_it and small hysteresis, the effectiveness of Al₂O₃/La₂O₃/InGaAs gate stacks with ultrathin La₂O₃ interfacial layers is in addition evaluated. The reduction of the La₂O₃ thickness to 0.4 nm in Al₂O₃/La₂O₃/InGaAs gate stacks leads to the decrease in hysteresis. On the other hand, D_it of the Al₂O₃/La₂O₃/InGaAs interfaces becomes higher than that of the La₂O₃/InGaAs ones, attributable to the diffusion of Al₂O₃ through La₂O₃ into InGaAs and resulting modification of the La₂O₃/InGaAs interface structure. As a result of the effective passivation effect of La₂O₃ on InGaAs, however, the Al₂O₃/10 cycle (0.4 nm) La₂O₃/InGaAs gate stacks can realize still lower D_it with maintaining small hysteresis and low leakage current than the conventional Al₂O₃/InGaAs MOS interfaces.