Functional nanocrystalline TiO2 thin films for UV enhanced highly responsive silicon photodetectors

Abstract

In this paper, we have studied the effect of nanocrystalline TiO2 functional layer on the performance of Si photodetectors. It was found that the electron affinity of the deposited TiO2 films is much lower (3.2 eV) than the conventional films of the value 3.9 eV. In addition, the band gap of these newly developed films was found to be 3.6 eV which makes the films transparent for band to band optical absorption. However, a very high absorption co efficient of the value 4.6 × 105 cm−1 and excitonic dissociation facilitate charge generation and transfer mechanisms in such films. It was found that the photodetector parameters like internal gain, response time, responsivity, detectivity, sensitivity and noise can be improved by inserting functional TiO2 layer to make either anisotype or isotype heterojunction with Si photodetectors. The major phenomena for such enhancements were found to be decrease in tunneling length and increased charge generation/transfer due to TiO2 nanocrystals. By this modified design, TiO2/p-Si hybrid device offer high responsivity of the value 23.07 A/W and detectivity of 4.5 × 1012 Jones for red light (620 nm) at an incident power of 1 mW/cm2. Furthermore, it was confirmed that faster devices with rise time of only 30 μs in broadband region from 425 to 620 nm can be made out of TiO2/n-Si configuration which allows slower diffusion of charge carriers. This study will provide a pathway to design ultramodern, highly responsive/sensitive and broadband Si photodetectors.