All‐Optical‐Input Transistors: Light‐Controlled Enhancement of Plasmon‐Induced Photocurrent

Abstract

Although phototransistors for controlling photocurrent with electricity have been studied intensively for several decades, transistors with all-optical inputs that can control the photocurrent with light have not been investigated thus far. In this paper, a plasmonic porous Ag/TiO 2 transistor is fabricated with all-optical inputs. One light input acts as the source to generate a plasmonic-hot-electron photocurrent, while the other gate light changes the current channel by adjusting the height of an Ag/TiO 2 Schottky barrier. As a result, the plasmon-induced photocurrent generated by the source light can be enhanced by several to one hundred times by controlling the gate light. In addition to signal enhancement, the device can also be used for signal modulation and switching.

Porous Ag/TiO2-Schottky-diode based plasmonic hot-electron photodetector with high detectivity and fast response

“…The response spectrum of the photodetector ranged from visible to near-infrared with a responsivity peak of 4 mA/W at 440 nm ( Figure 1C). Because the energy of the visible light (1.6-3.1 eV for 400-780 nm photons) was lower than the bandgap of anatase TiO 2 (3.17 eV) [24,26,27], the photoresponse shown in Figure 1C is believed to be a plasmon-participating photoresponse, which can be proved by the agreement in wavelength between the photocurrent responsivity peak and surface plasmon resonance peak of the porous Ag/TiO 2 membrane ( Figure S3) [14,24,28]. Figure 1D illustrates the energy band diagram for the plasmon-participating photoresponse, where incident light excites surface plasmons on the porous Ag layer and some of the plasmons then decay into hot-electrons and holes [29].…”

“…Due to certain energy distribution of the hot-electrons [1], a lower Schottky barrier can enable more hot-electrons to cross over it and contribute to a higher responsivity. In our previous work, the Ag/TiO 2 Schottky barrier was proved to result from the chemisorbed oxygen on the surface of porous TiO 2 , and the height of the Schottky barrier can be decreased by ultraviolet light illumination through a process of oxygen desorption, however, the decreased Schottky barrier will turn back to a high value as the ultraviolet light is turned off [24]. In order to obtain a permanent decreased Schottky barrier, we propose a method of long-hours ultraviolet light illumination in vacuum ( Figure 4A-C).…”

“…Thus, the hot-electron photodetector based on a Ag/TiO 2 Schottky junction may have high detectivity and a fast response speed. However, the fabrication of a Ag/TiO 2 Schottky junction is full of challenges due to the fact that the work function of Ag is too low for Ag to form a Schottky contact with n-type TiO 2 [24], so that the Ag/TiO 2 based hot-electron photodetector has not yet been developed successfully. Recently, our work showed that the chemisorbed oxygen on the surface of TiO 2 can change the surface energy band of TiO 2 , which enables the formation of Schottky contact between TiO 2 and Ag [24].…”

Photodoping of metal oxide nanocrystals for multi-charge accumulation and light-driven energy storage

“…The possibility to modulate the carrier density of doped semiconductors via photodoping could be exploited to design transistors in which the gate input is replaced with light, or even developing all-opticalinput. 88,89 In fact, in a recent work MO NCs were employed as all-optical light-driven charge injection tools to inject multiple electrons into 2D TMDs, in analogy to 2D material gating. 89 This together displays that MO NCs photodoping opens horizons for novel application spaces as active elements in self-powered nano-electronics.…”

Light-modulated vertical heterojunction phototransistors with distinct logical photocurrents

“…A method involving 450 nm light illumination that can expand the photodetection range and suppress the dark current was proposed by Fang et al 34 . Furthermore, Gao et al 35 demonstrated Schottky phototransistors with enhanced photocurrents due to a Schottky–Ohmic transformation induced by light. As we known, comprehensive modulation of the photocurrent magnitude, operating speed, and signal direction of phototransistors by modulation light input is lacking, where light modulation hopefully offers a versatile platform for replacing electrical modulation to explore more intriguing optoelectronic devices.…”