Ultrasensitive Photodetections Based on Monolayer MoS2 Integrated with Surface-Acoustic-Wave Devices
Chih-Ya Tsai1*, Hung-Chieh Fu1, Wei-Sheng Chen2, Guo-Wei Wu2, Hui-Ling Kao2, Wen-Hao Chang1
1Electrophysics, National Chiao Tung University, Hsinchu, Taiwan
2Electronic Engineering, Chung Yuan Christian University, Taoyuan, Taiwan
* Presenter:Chih-Ya Tsai, email:walkingyaya@gmail.com
Monolayer molybdenum disulphide (MoS2) have attracted considerable interests in optoelectronic applications because its direct-band gap near 1.8 eV for efficient optical absorption and emissions. It has been reported that using MoS2 as the photodetection layer can improve the responsivity up to 103 A/W [1-2]. These devices [1] show sensitive response to light with a power density down to 24 µW/cm2. However, a large gate voltage ranging from 70~80 V [1-2] is necessary in order to enhance the photogain. Here we demonstrate an ultrasensitive photodetector based on a surface acoustic wave (SAW) device with a monolayer MoS2 as the sensing layer. A CVD grown, large-area monolayer MoS2 film was integrated on the delay-line area of a SAW device based on a piezoelectric ST-quartz substrate. A maximum down shift of 35 kHz from the original SAW resonant frequency (194 MHz) is observed as illuminated by a 532 nm laser with 1 mW while a very low driving voltage of 3V is applied. The linear response region varies from 10 µW/cm2 to 0.01 W/cm2, revealing an ultrasensitive photodetection. Based on a bimolecular recombination model in the high-excitation regime, we estimate an effective electromechanical coefficient κ2 of 0.033% for ST-cut quartz, which is close to the theoretical value of κ2= 0.11%. Our results demonstrate the feasibility of using monolayer MoS2 as the sensing layer in a SAW device for optical sensing applications.

References:
1. Lopez-Sanchez, O. et al., “Ultrasensitive photodetectors based on monolayer MoS2,” Nat. Nanotechnol. 8, 497 (2013).
2. Furchi, M. M. et al., “Mechanisms of photoconductivity in atomically thin MoS2,” Nano Lett. 14, 6165 (2014).


Keywords: molybdenum disulphide, photodetection, surface acoustic wave