Abstract-Strong negative terahertz photoconductivity in photoexcited graphene

• Maixia Fu^a, b, 
• Xinke Wang^a, 
• Jiasheng Ye^a, 
• Shengfei Feng^a, 
• Wenfeng Sun^a, 
• Peng Han^a,
• Yan Zhang^a, , 

• ^a Department of Physics, Capital Normal University, Beijing Key Lab for Metamaterials and Devices, Key Lab of Terahertz Optoelectronics, Ministry of Education, and Beijing Advanced Innovation Center for Imaging Technology, Beijing 100048, China
• ^b College of Information Science and Engineering, Henan University of Technology, Key Laboratory of Grain Information Processing and Control, Ministry of Education, Zhengzhou, Henan 450001, China
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http://www.sciencedirect.com/science/article/pii/S0030401817300603?np=y&npKey=471b13ae12faa43f83824dc4b2431c665331c62b0344b4566b15cd4bceb13752

Terahertz (THz) response of a chemical vapor deposited graphene on a quartz substrate has been investigated by using an ultrafast optical-pump THz-probe spectroscopy. Without photoexcitation, the frequency-dependence optical conductivity shows a strong carrier response owing to the intrinsically doped graphene. Upon photoexcitation, an enhancement in THz transmission is observed and the transmission increases nonlinearly with the increase of pump power, which is rooted in a reduction of intrinsic conductivity arising from the strong enhancement of carrier scattering rather than THz emission occurrence. The modulation depth of 18.8% was experimentally achieved, which is more than four times greater than that of the previous reported. The photoinduced response here highlights the variety of response possible in graphene depending on the sample quality, carrier mobility and doping level. The graphene provides promising applications in high-performance THz modulators and THz photoelectric devices.