Ultrahigh photosensitivity and detectivity of hydrogen-treated TiO₂ nanorod array/SiO₂/Si heterojunction broadband photodetectors and its mechanism

It is demonstrated that hydrogen treatment as a simple, effective strategy can greatly improve the broadband photo-responsive performance of pristine TiO₂ nanorod arrays (NRAs)/SiO₂/n-Si heterojunctions. The hydrogen-treated TiO₂ NRAs/SiO₂/n-Si heterojunction shows a stable, repeatable and broadband photo response from 365 nm to 980 nm at 100 μW cm^-2. The responsivity (R) of H:TiO₂ NRAs/SiO₂/n-Si approaches the ultrahigh value of 468 A W^-1 and it has an outstanding detectivity (D∗) of 1.96 × 10¹⁴ cm Hz^1/2 W^-1 and an excellent sensitivity (S) of 2.63 × 10⁷ cm² W^-1, in contrast to the values of R (10^-6-10^-1 A W^-1) or S (2 × 10³ cm² W^-1) from reported TiO₂ nanofilm/TiO₂ NRAs/n-Si(111) photodetectors, indicating a huge responsivity enhancement of up to 4-8 orders of magnitude. Additionally, the response and recovery time are extremely short (3.5-3.9 ms). The comprehensive characteristics make the device stand out among the previously reported 1D metal oxide nanostructure/Si based photodetectors. In fact, the R, S and D∗ values of the heterojunction are 2-4 orders of magnitude higher than those of some new 2D nanomaterials/Si based photodetectors. The excellent photo-responsive performance may be attributed to the energy band structure of the TiO₂@TiO_2-xH_x core/shell structure, the interface effect of the TiO₂@TiO_2-xH_x/Si heterojunction, etc. This research provides a new concept for the design of other metal oxide based heterojunction photodetectors.