TiO₂@TiO_2-xHx core-shell nanoparticle film/Si heterojunction for ultrahigh detectivity and sensitivity broadband...

A simple hydrogenation treatment is used to synthesize unique oxygen-deficient TiO₂ with a core/shell structure (TiO₂@TiO_2-xH_x), superior to the high H₂-pressure process (under 20 bar for five days). It is demonstrated that oxygen-deficient TiO₂ nanoparticle film/Si heterojunction possesses improved photoresponse performance compared to the untreated TiO₂ nanoparticle film/Si heterojunction. Particularly, under 900 nm of 0.5 μW cm^-2, the oxygen-deficient TiO₂ nanoparticle film (TiO₂@TiO_2-xH_x core-shell nanoparticle film)/Si heterojunction shows high responsivity (R) of 336 A W^-1, prominent sensitivity (S) of 1.3 × 10⁷ cm² W^-1, accompanied with a fast rise and decay time of 6 and 5 ms, respectively. Significantly, the detectivity (D*) of the photodetector is up to 1.17 × 10¹⁴ cm Hz^1/2 W^-1, which is better than that reported in metal oxide nanomaterials/Si heterojunction photodetectors, and is 4-5 orders of magnitude higher than some 2D nanosheets/Si heterojunctions of 10⁹-10¹⁰ cm Hz^1/2 W^-1, indicating the excellent ability to detect weak signals. The oxygen vacancies generated in amorphous shell TiO_2-xH_x make the Fermi level of TiO_2-x shift near the conduction band minimum and can lead to reduced dark current. The high absorption and reduced dark current of the heterojunction ensure excellent photoresponse properties of oxygen-deficient TiO₂ nanoparticle film/Si heterojunction. The H-reduced oxygen-deficient amorphous shell may be an excellent candidate to enhance the photoresponse performance of metal oxide/Si heterojunction.