- Nano Express
- Open Access
Bias-dependent photoresponsivity of multi-layer MoS2 phototransistors
© The Author(s). 2017
- Received: 1 September 2017
- Accepted: 9 November 2017
- Published: 21 November 2017
We studied the variation of photoresponsivity in multi-layer MoS2 phototransistors as the applied bias changes. The photoresponse gain is attained when the photogenerated holes trapped in the MoS2 attract electrons from the source. Thus, the photoresponsivity can be controlled by the gate or drain bias. When the gate bias is below the threshold voltage, a small amount of electrons are diffused into the channel, due to large barrier between MoS2 and source electrode. In this regime, as the gate or drain bias increases, the barrier between the MoS2 channel and the source becomes lower and the number of electrons injected into the channel exponentially increases, resulting in an exponential increase in photoresponsivity. On the other hand, if the gate bias is above the threshold voltage, the photoresponsivity is affected by the carrier velocity rather than the barrier height because the drain current is limited by the carrier drift velocity. Hence, with an increase in drain bias, the carrier velocity increases linearly and becomes saturated due to carrier velocity saturation, and therefore, the photoresponsivity also increases linearly and becomes saturated.
Recently, transition metal dichalcogenide (TMD) materials including molybdenum disulfide (MoS2) and tungsten diselenide (WSe2) have received considerable attention as the channel material for next generation nanoelectronic devices [1–6]. In particular, thin-film transistors that use MoS2 exhibit interesting electric characteristics such as high electron mobility (~ 200 cm2 V−1 s−1), high current ON/OFF ratio (~ 108), and low subthreshold swing (~ 70 mV dec−1) in a single-layer MoS2 transistor . In addition, MoS2 is attracting attention as a light absorbing layer in optoelectronic devices because of its bandgap energy (single-layer MoS2 has a direct bandgap of 1.8 eV  and bulk MoS2 has an indirect bandgap of 1.2 eV ) and large absorption coefficient (α = 1–1.5 × 106 cm−1 for single-layer  and 0.1–0.6 × 106 cm−1 for bulk ). Hence, phototransistors using MoS2 have a low dark current in the OFF state and high photoresponsivity. The performance of MoS2 phototransistors have been improved by introducing an additional layer such as graphene [12–15], quantum dot [16–18], organic dye , WS2 [20–22], ZnO , and p-type MoS2  or by changing the gate dielectric [7, 25, 26]. In this way, many studies have been actively conducted to improve the photoresponsivity through additional manufacturing processes; however, there is a lack of research on the gain control and specific understanding of MoS2 phototransistors. When gain control is enabled, a wide range of light intensities can be reliably detected, and the gain can be increased without any additional manufacturing process. In this context, we investigated the bias (drain or gate)-controlled photoresponsivity in multi-layer MoS2 phototransistors.
We fabricated a multi-layer MoS2-based phototransistor and investigated its bias (drain or gate)-controlled photoresponsivity in detail. The change in photoresponsivity according to the bias can be classified into two cases: when the gate bias is smaller than the threshold voltage (OFF state) and when the gate bias is larger than the threshold voltage (ON state). When the gate bias is smaller than the threshold voltage, a small amount of electrons are diffused into the channel, due to large barrier between MoS2 and source electrode. As the gate or drain biases increase, the height of the barrier decreases and the number of electrons injected into the channel for neutrality increases. As a result, the photoresponsivity increases exponentially. On the other hand, when the gate bias is greater than the threshold voltage, the photoresponsivity is affected by the carrier velocity rather than the height of barrier because current is limited by carrier drift velocity. As the drain bias increases, the carrier velocity increases linearly and becomes saturated. Therefore, the photoresponsivity increases linearly and becomes saturated. We were able to understand the responsivity variations in multi-layer MoS2-based phototransistors according to the gate or drain bias. Thereby, the gain can be controlled to increase the range of application of the MoS2 phototransistor and to operate optimally, depending on the purpose and environment.
This research was supported by the National Research Foundation of Korea (NRF) grant funded by the Ministry of Education (MOE) (NRF-2017R1D1A1B03034785) and by the Ministry of Science, ICT & Future Planning (MSIP) (NRF-2015M2B2A9033138). This work was also supported by the “Human Resources Program in Energy Technology” of the Korea Institute of Energy Technology Evaluation and Planning (KETEP), granted financial resource from the Ministry of Trade, Industry & Energy, Republic of Korea (no. 20164030201380).
JP and YP manufactured the phototransistor. JP and GY measured the phototransistor characteristics. JP, GY, and JH analyzed the measured data. JH planned and supervised the study. All authors read and approved the final manuscript.
The authors declare that they have no competing interests.
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- Yoon Y, Ganapathi K, Salahuddin S (2011) How good can monolayer MoS2 transistors be? Nano Lett 11:3768–3773View ArticleGoogle Scholar
- Lv R, Robinson JA, Schaak RE, Sun D, Sun Y, Mallouk TE, Terrones M (2015) Transition metal dichalcogenides and beyond: synthesis, properties, and applications of single- and few-layer nanosheets. Acc Chem Res 48:56–64View ArticleGoogle Scholar
- Duan X, Wang C, Pan A, Yu R, Duan X (2015) Two-dimensional transition metal dichalcogenides as atomically thin semiconductors: opportunities and challenges. Chem Soc Rev 44:8859–8876View ArticleGoogle Scholar
- Li H, Wu J, Yin Z, Zhang H (2014) Preparation and applications of mechanically exfoliated single-layer and multilayer MoS2 and WSe2 nanosheets. Acc Chen Res 47:1067–1075View ArticleGoogle Scholar
- Jariwala D, Sangwan VK, Lauhon LJ, Marks TJ, Hersam MC (2014) Emerging device applications for semiconducting two-dimensional transition metal dichalcogenides. ACS Nano 8:1102–1120View ArticleGoogle Scholar
- Wang QH, Kalantar-Zadeh K, Kis A, Coleman JN, Strano MS (2012) Electronics and optoelectronics of two-dimensional transition metal dichalcogenides. Nature Nanotech 7:699–712View ArticleGoogle Scholar
- Radisavljevic B, Radenovic A, Brivio J, Giacometti V, Kis A (2011) Single-layer MoS2 transistors. Nature Nanotech 6:147–150View ArticleGoogle Scholar
- Mak KF, Lee C, Hone J, Shan J, Heinz TF (2010) Atomically thin MoS2: a new direct-gap semiconductor. Phys Rev Lett:105, 136805Google Scholar
- Kam KK, Parkinson BA (1982) Detailed photocurrent spectroscopy of the semiconducting group VIB transition metal dichalcogenides. J Phys Chem 86:463–467View ArticleGoogle Scholar
- Bernardi M, Palummo M, Grossman JC (2013) Extraordinary sunlight absorption and one nanometer thick photovoltaics using two-dimensional monolayer materials. Nano Lett 13:3664–3670View ArticleGoogle Scholar
- Beal AR, Hughes HP (1979) Kramers-Kronig analysis of the reflectivity spectra of 2H-MoS2, 2H-MoSe2 and 2H-MoTe2. J Phys C: Solid Phys 12:881–890View ArticleGoogle Scholar
- Hau X, Juanxia W, Feng Q, Mao N, Wang C, Zhang J (2014) High responsivity and gate tunable graphene-MoS2 hybrid phototransistor. Small 10:2300–2306View ArticleGoogle Scholar
- Zhang W, Chuu C-P, Huang J-K, Chen C-H, Tsai M-L, Chang Y-H, Liang C-T, Chen Y-Z, Chueh Y-L, He J-H, Chou M-Y, Li L-J (2014) Ultrahigh-gain photodetectors based on atomically thin graphene-MoS2 heterostructures. Sci Rep 4:3826View ArticleGoogle Scholar
- Kwak JY, Hwang J, Calderon B, Alsalman H, Spencer MG (2016) Long wavelength optical response of graphene-MoS2 heterojunction. Appl Phys Lett 108:091108View ArticleGoogle Scholar
- Henck H, Pierucci D, Chaste J, Naylor CH, Avila J, Balan A, Silly MG, Asensio MC, Sirotti F, Charlie Johnson AT, Lhuillier E, Ouerghi A (2016) Electrolytic phototransistor based on graphene-MoS2 van der waals p-n heterojunction with tunable photoresponse. Appl Phys Lett 109:113103View ArticleGoogle Scholar
- Kufer D, Nikitskiy I, Lasanta T, Navickaite G, Koppens FHL, Konstantatos G (2015) Hybrid 2D-0D MoS2-PbS quantum dot photodetectors. Adv Mater 27:176–180View ArticleGoogle Scholar
- Caiyun Chen, Hong Qiao, Shenghuang Lin, Chi Man Luk, Yan Liu, Zaiquan Xu, Jingchao Song, Yunzhou Xue, Delong Li, Jian Yuan, Wenzhi Yu, Chunxu Pan, Shu Ping Lau, and Qiaoliang Bao. Highly responsive MoS2 photodetectors enhanced by graphene quantum dots. Sci Rep. 2015;5;11830Google Scholar
- Schornbaum J, Winter B, Schieβl SP, Gannott F, Katsukis G, Guldi DM, Spiecker E, Zaumseil J (2014) Epitaxial growth of PbSe quantum dots on MoS2 nanosheets and their near-infrared photoresponse. Adv Funct Mater 24:5798–5806View ArticleGoogle Scholar
- Seong Hun Y, Lee Y, Jang SK, Kang J, Jeon J, Lee C, Lee JY, Kim H, Hwang E, Lee S, Cho JH (2014) Dye-sensitized MoS2 photodetector with enhanced spectral photoresponse. ACS Nano 8:8285–8291View ArticleGoogle Scholar
- Huo N, Kang J, Wei Z, Li S-S, Li J, Wei S-H (2014) Novel and enhanced optoelectronics performances of multilayer MoS2-WS2 heterostructure transistors. Adv Funct Mater 24:7025–7031View ArticleGoogle Scholar
- Xue Y, Zhang Y, Liu Y, Liu H, Song J, Sophia J, Liu J, Xu Z, Xu Q, Wang Z, Zheng J, Liu Y, Li S, Bao Q (2016) Scalable production of a few-layer MoS2/WS2 vertical heterojunction array and its application for photodetectors. ACS Nano 10:573–580View ArticleGoogle Scholar
- Yifei Y, Shi H, Liqin S, Huang L, Liu Y, Jin Z, Purezky AA, Geohegan DB, Kim KW, Zhang Y, Cao L (2015) Equally efficient interlayer exciton relaxation and improved absorption in epitaxial and nonepitaxial MoS2/WS2 heterostructures. Nano Lett 15:486–491View ArticleGoogle Scholar
- Hsiao Y-J, Fang T-H, Ji L-W, Yang B-Y (2015) Red-shift effect and sensitive responsivity of MoS2/ZnO flexible photodetectors. Nanoscale Res Lett 10:443View ArticleGoogle Scholar
- Ye J, Li X, Zhao J, Mei X, Li Q (2015) A facile way to fabricate high-performance solution-processed n-MoS2/p-MoS2 bilayer photodetectors. Nanoscale Res Lett 10:454View ArticleGoogle Scholar
- Kim S, Konar A, Hwang W-S, Lee JH, Lee J, Yang J, Jung C, Kim H, Yoo J-B, Choi J-Y, Jin YW, Lee SY, Jena D, Choi W, Kim K (2012) High-mobility and low-power thin-film transistors based on multilayer MoS2 crystals. Nat Commun 3:1011View ArticleGoogle Scholar
- Choi W, Cho MY, Konar A, Lee JH, Cha G-B, Hong SC, Kim S, Kim J, Jena D, Joo J, Kim S (2012) High-detectivity multilayer MoS2 phototransistors with spectral response from ultraviolet to infrared. Adv Mater 24:5832–5836View ArticleGoogle Scholar
- Novoselov KS, Jiang D, Schedin F, Booth TJ, Khotkevich VV, Morozov SV, Geim AK (2005) Two-dimensional atomic crystals. PNAS 102:10451–10453View ArticleGoogle Scholar
- Wakabayashi N, Smith HG, Nicklow RM (1975) Lattice dynamics of hexagonal MoS2 studied by neutron scattering. Phys Rev B 12:659–663View ArticleGoogle Scholar
- Lee C, Yan H, Brus LE, Heinz TF, Hone J, Ryu S (2010) Anomalous lattice vibrations of single-and few-layer MoS2. ACS Nano 4:2695–2700View ArticleGoogle Scholar
- Adinolfi V, Sargent EH (2017) Photovoltage field-effect transistors. Nature 542:324–327View ArticleGoogle Scholar
- Liu J, Yin Y, Yu L, Shi Y, Liang D, Dai D (2017) Silicon-graphene conductive photodetector with ultra-high responsivity. Sci Rep 7:40904View ArticleGoogle Scholar
- Lopez-Sanchez O, Lembke D, Kayci M, Radenovic A, Kis A (2013) Ultrasensitive photodetectors based on monolayer MoS2. Nature Nanotech 8:497–501View ArticleGoogle Scholar
- An X, Liu F, Jung YJ, Kar S (2013) Tunable graphene-silicon heterojunctions for ultrasensitive photodetection. Nano Lett 13:909–916View ArticleGoogle Scholar