Oxide Trapping in the InGaAs– System and the Role of Sulfur in Reducing the Trap Density

Trap spectroscopy by charge injection and sensing method was applied to the In_0.53Ga_0.47As-Al₂O₃ system, yielding the spatial and energetic distribution of the traps inside the Al₂O₃ layer. The trap density inside the atomic-layer-deposited (ALD) Al₂O₃ layer was found to be significantly reduced by (NH₄)₂S treatment of the InGaAs surface prior to the Al₂O₃ deposition. Indium concentration inside the Al₂O₃ layer was found to be reduced once the InGaAs surface is (NH₄)₂S treated prior to the Al₂O₃ deposition as measured by time-of-flight secondary ion mass spectroscopy, indicating indium as a possible origin of the oxide traps. The results suggest a new mechanism for the sulfur action at the InGaAs surface, which might be responsible for the transistor performance improvements observed after ( NH₄)₂S passivation. This mechanism involves sulfur as an indium diffusion/segregation barrier stabilizing the InGaAs surface during the ALD Al₂O₃ deposition, lowering the oxide trap density. This, in turn, improves the electron mobility through a reduction in the Coulomb scattering of the carriers due to border traps and improves the device drive current.