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

Abstract

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.