Abstract
2-Dimensional structures with swift optical response have several technological advantages, for example they could be used as components of ultrafast light modulators, photo-detectors, and optical switches. Here we report on the fast photo switching behavior of thin films of liquid phase exfoliated MoS2, when excited with a continuous laser of λ = 658 nm (E = 1.88 eV), over a broad range of laser power. Transient photo-conductivity measurements, using an optical pump and THz probe (OPTP), reveal that photo carrier decay follows a bi-exponential time dependence, with decay times of the order of picoseconds, indicating that the photo carrier recombination occurs via trap states. The nature of variation of photocurrent with temperature confirms that the trap states are continuously distributed within the mobility gap in these thin film of MoS2, and play a vital role in influencing the overall photo response. Our findings provide a fundamental understanding of the photo-physics associated with optically active 2D materials and are crucial for developing advanced optoelectronic devices.
Highlights
2-Dimensional structures with swift optical response have several technological advantages, for example they could be used as components of ultrafast light modulators, photo-detectors, and optical switches
Correspondence and requests for materials should be addressed to S.T. or S.G. www.nature.com/scientificreports/. Since these materials are directly exfoliated in suspensions, they can be used as inks and can be used to cast thin films on a variety of substrates without any additional processing or transferring
In this letter we demonstrate that thin films of such liquid phase exfoliated MoS2 can be used as photo-detectors with ultrafast photo-carrier generation and recombination times
Summary
Sujoy Ghosh[1], Andrew Winchester[1], Baleeswaraiah Muchharla[1], Milinda Wasala[1], Simin Feng[2], Ana Laura Elias[2], M. In order to understand the distribution of the trap states in the MoS2 photo detectors, we have performed measurements of Iph at very low light intensities and at different temperatures For this purpose a Uniphase Helium Neon Gas Laser (λ = 633 nm, E = 1 .95 eV) with a maximum power output of 1mw was used. Detailed photocurrent measurements as a function of temperature show that these films contain extended trap states, which mainly arise due to the disorder caused by the random orientation of the stacked layers of the exfoliated flakes This results in a faster recombination of the charge carriers, and reduces the responsivity of these materials when compared to several recently studied mechanically exfoliated and Chemical Vapor Transport grown 2D layered chalcogenides[27,28,29,30,31,32,33,34,35]. The results presented in this manuscript will open up similar investigations, and will motivate the development of photoactive nano-materials and composites for several opto-electronic applications
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