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This research aims to quantitatively analyze defect density distribution in silicon-based MIS photoelectrodes to improve charge transport efficiency.

March 25, 2026

Spatially Quantitative Profiling of Defect Density for Hydrogen-Induced Passivation Mechanism of Metal–Insulator–Semiconductor Photoanodes

Key Points

This research aims to quantitatively analyze defect density distribution in silicon-based MIS photoelectrodes to improve charge transport efficiency.
Developed an integrated multicapacitance methodology combining DLCP and C-V techniques.
Used equivalent circuit modeling for refined analysis of space-charge capacitance.
Measured interface and bulk defect charge density during the optimization of passivation processes.
Al2O3 reduced the interface defect density from approximately 2.9 × 10^16 to 1.4 × 10^16 cm^-3.
Optimal passivation achieved at deposition temperature of ~160 °C followed by 350 °C annealing.
The optimized photoanode exhibited an onset potential of 0.88 V and an ABPE of 2.91% with 120 hours of stability.

Abstract

Silicon-based metal-insulator-semiconductor (MIS) photoelectrodes provide a built-in field for photoelectrochemical water splitting but suffer from inefficient charge transport due to carrier recombination at defect sites within the space-charge region. The insulating layer fabricated by atomic layer deposition (ALD) is critical for defect passivation and requires carefully engineered deposition and annealing processes for optimal performance. This necessitates the quantitative analysis of defect density distribution. However, such analysis remains impeded by intrinsic limitations of conventional single-capacitance techniques and the influence of tunneling leakage currents. This paper describes an integrated multicapacitance methodology that combines drive-level capacitance profiling (DLCP) and capacitance-voltage (C-V) techniques to quantify both interface (Nit) and bulk defect charge density (NDLCP) within the space-charge region, using the space-charge capacitance refined by MIS-adapted multicomponent equivalent circuit modeling. This approach reveals that Al2O3 reduces the Nit at n-Si/ITO interface from approximately 2.9 × 1016 to 1.4 × 1016 cm-3, while simultaneously profiling the variation of NDLCP and depletion width. Furthermore, systematic DLCP/C-V analysis enables the design of a tailored passivation protocol by tuning ALD deposition (Tdep) and annealing temperatures to leverage the hydrogen-induced mechanism. Optimal passivation is achieved at a moderate Tdep (∼160 °C) followed by 350 °C annealing, which balances sufficient hydrogen content and suitable structural properties of the Al2O3 film without introducing additional bulk defects during annealing. Eventually, the optimized n-Si/SiOx/Al2O3/ITO/Ni photoanode exhibits an onset potential of 0.88 V vs RHE and an applied bias photon-to-current efficiency (ABPE) of 2.91%, with a long-term stability of 120 h.

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Spatially Quantitative Profiling of Defect Density for Hydrogen-Induced Passivation Mechanism of Metal–Insulator–Semiconductor Photoanodes

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