Native Defect-Dependent Ultrafast Carrier Dynamics in p-Type Dopable Wide-Bandgap NiO

Area of Science:

• Materials Science
• Solid State Physics
• Photochemistry

Background:

• Nickel oxide (NiO) is a p-type metal oxide with significant applications in optoelectronics and photocatalysis.
• Understanding carrier dynamics in NiO is crucial for device optimization but remains underexplored.
• Native defects significantly influence the electronic properties of NiO.

Purpose of the Study:

• To investigate the carrier dynamics in NiO thin films with different native defects using femtosecond transient absorption spectroscopy.
• To elucidate the role of oxygen vacancies (VO) and nickel vacancies (VNi) in carrier behavior.
• To provide insights into optimizing NiO-based device performance.

Main Methods:

• Femtosecond transient absorption spectroscopy was used to probe carrier dynamics.
• Two types of NiO films were studied: undoped NiO with oxygen vacancies and O-rich NiO (NiO1+δ) with nickel vacancies.
• Spectroscopic analysis focused on photoinduced absorption and photobleaching signals.

Main Results:

• Distinct spectral features were observed: broad photoinduced absorption in undoped NiO and photobleaching in O-rich NiO.
• Small electron polarons (SEPs) formed rapidly (<200 fs).
• Carrier trapping occurred at localized states (1-8 ps for undoped NiO, 5-7 ps for NiO1+δ), followed by slower trapping/recombination via native defects (200 ps for VO, ~2 ns for VNi).

Conclusions:

• Native defects (VO and VNi) significantly alter carrier dynamics in NiO films.
• The study reveals distinct pathways for photogenerated carrier trapping and recombination.
• These findings offer fundamental insights for designing high-performance NiO-based optoelectronic and photocatalytic devices.