Recently, the research group in the Key Laboratory of Materials Physics, Institute of Solid State Physics, Hefei Institutes of Physical Sciences has made progress in detectivity and response speed improvement of the plasmonic hot electron photodetector based on porous Ag/TiO2 Schottky diode.
The plasmonic hot-electron photodetector composed of metal/semiconductor Schottky junction is a new kind of photodetector, which could enable response to the photos with energy below the bandgap of the semiconductor substrate and have tunable spectral response peak by simply adjusting the metal nanostructure.
In the past several years, a lot of efforts are focused on improving the performance of photovoltaic hot-electron photodetectors. However, the detectivity and response time of photovoltaic hot-electron photodetector, which are of more importance than responsivity in the applications of optical imaging and optical communication, have not got much improvement.
Ag/TiO2 Schottky junction is considered to be an ideal material for plasmonic hot-electron photodetector. On one hand, Ag has the advantages of high plasmon electric fields density and narrow hot electrons energy distribution, which can lead to higher photoelectric conversion efficiency. On the other hand, TiO2 has high states density in the TiO2 conduction band, which enables fast electron injection. Thus, the hot-electron photodetector based on Ag/TiO2 Schottky junction may have high detectivity and fast response speed.
In this work, scientists synthesized porous Ag/TiO2-Schottky-diode based plasmonic hot-electron photodetector (Figure 1).
The photodetector showed a fast response speed with rise and fall time of 112 ¦Ìs and 24 ¦Ìs, respectively, and a high detectivity of 9.8 ¡Á 1010 cmHz1/2/W under 450 nm light illumination at zero bias voltage (Figure 2); both of these values were substantially better than those previously reported.
By decreasing the Schottky barrier through a deep ultraviolet light illumination process, the responsivity of device at 450 nm increased from 3.4 mA/W to 7.4 mA/W.
This work was supported by the National Natural Science Foundation of China (NOs. 51701207, 51471162, 51502294, 51671183), the CAS/SAFEA International Partnership Program for Creative Research Teams.
Link to the paper: https://www.degruyter.com/view/j/nanoph.ahead-of-print/nanoph-2019-0094/nanoph-2019-0094.xml?format=INT&tdsourcetag=s_pcqq_aiomsg
Figure1: Photodetector structure and plasmonic hot electron participated photoresponse.
(A) Schottky I-V curve of porous Ag/TiO2 composite film measured in vacuum. (B) SEM images of the porous Ag/TiO2 membrane. (C) Spectral responses of the porous Ag/TiO2 photodetector. (D) Band diagram for the generation of plasmonic hot electrons photocurrent. (Image by GAO Xudong)
Figure 2: Photocurrent response under 450 nm light illumination.
(A) Response under pulsed light illumination with different power at zero bias voltage. (B) Fitting curve of the relationship between the photocurrent and light power. (C) A single normalized cycle of the photocurrent response. (Image by GAO Xudong)