TiO@TiOHx core-shell nanoparticle film/Si heterojunction for ultrahigh detectivity and sensitivity broadband photodetector.

A simple hydrogenation treatment is used to synthesize unique oxygen-deficient TiO with a core/shell structure (TiO@TiOH), superior to the high H-pressure process (under 20 bar for five days). It is demonstrated that oxygen-deficient TiO nanoparticle film/Si heterojunction possesses improved photoresponse performance compared to the untreated TiO nanoparticle film/Si heterojunction. Particularly, under 900 nm of 0.5 μW cm, the oxygen-deficient TiO nanoparticle film (TiO@TiOH core-shell nanoparticle film)/Si heterojunction shows high responsivity (R) of 336 A W, prominent sensitivity (S) of 1.3 × 10 cm W, 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 × 10 cm Hz W, 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 10-10 cm Hz W, indicating the excellent ability to detect weak signals. The oxygen vacancies generated in amorphous shell TiOH make the Fermi level of TiO 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 TiO 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.