Journal
ACS PHOTONICS
Volume 6, Issue 4, Pages 953-960Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acsphotonics.8b01639
Keywords
hot carriers; TiN thin films; TiO2-x; sub-bandgap photodetection; CMOS compatible
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Funding
- EPSRC Reactive Plasmonics Program [EP/M013812/1]
- Lee Lucas Chair in Physics
- Henry Royce Institute through EPSRC [EP/R00661X/1]
- Leverhulme Trust [RPG-2016-064]
- WiTec scholarship for studies in nanophotonics
- EPSRC [EP/M013812/1, EP/P02520X/1] Funding Source: UKRI
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We investigate titanium nitride (TiN) thin film coatings on silicon for CMOS-compatible sub-bandgap charge separation upon incident illumination, which is a key feature in the vast field of on-chip photodetection and related integrated photonic devices. Titanium nitride of tunable oxidation distributions serves as an adjustable broadband light absorber with high mechanical robustness and strong chemical resistivity. Backside-illuminated TiN on p-type Si (pSi) constitutes a self-powered and refractory alternative for photodetection, providing a photoresponsivity of about similar to 1 mA/W at 1250 nm and zero bias while outperforming conventional metal coatings such as gold (Au). Our study discloses that the enhanced photoresponse of TiN/pSi in the near-infrared spectral range is directly linked to trap states in an ultrathin TiO2-x interfacial interlayer that forms between TiN and Si. We show that a pSi substrate in conjunction with a few nanometer thick amorphous TiO2-x film can serve as a platform for photocurrent enhancement of various other metals such as Au and Ti. Moreover, the photoresponse of Au on a TiO2-x/pSi platform can be increased to about 4 mA/W under 0.45 V reverse bias at 1250 nm, allowing for controlled photoswitching. A clear deviation from the typically assumed Fowler-like response is observed, and an alternative mechanism is proposed to account for the metal/semiconductor TiO2-x interlayer, capable of facilitating hole transport.
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