Large Lateral Photovoltaic Effect in MoS2/GaAs Heterojunction

Nanoscale Research Letters, Oct 2017

Molybdenum disulfide (MoS2) nanoscaled films are deposited on GaAs substrates via magnetron sputtering technique, and MoS2/GaAs heterojunctions are fabricated. The lateral photovoltaic effect (LPE) of the fabricated MoS2/GaAs heterojunctions is investigated. The results show that a large LPE can be obtained in the MoS2/n-GaAs heterojunction. The LPE exhibits a linear dependence on the position of the laser illumination and the considerably high sensitivity of 416.4 mV mm− 1. This sensitivity is much larger than the values in other reported MoS2-based devices. Comparatively, the LPE in the MoS2/p-GaAs heterojunction is much weaker. The mechanisms to the LPE are unveiled by constructing the energy-band alignment of the MoS2/GaAs heterojunctions. The excellent LPE characteristics make MoS2 films combined with GaAs semiconductors promising candidates for the application of high-performance position-sensitive detectors.

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Large Lateral Photovoltaic Effect in MoS2/GaAs Heterojunction

Hao et al. Nanoscale Research Letters Large Lateral Photovoltaic Effect in MoS /GaAs Heterojunction 2 Lanzhong Hao 0 1 Yunjie Liu 1 Zhide Han 1 Zhijie Xu 1 Jun Zhu 0 0 State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China , Chengdu 610054 , People's Republic of China 1 College of Science, China University of Petroleum , Qingdao 266580, Shandong , People's Republic of China Molybdenum disulfide (MoS2) nanoscaled films are deposited on GaAs substrates via magnetron sputtering technique, and MoS2/GaAs heterojunctions are fabricated. The lateral photovoltaic effect (LPE) of the fabricated MoS2/GaAs heterojunctions is investigated. The results show that a large LPE can be obtained in the MoS2/n-GaAs heterojunction. The LPE exhibits a linear dependence on the position of the laser illumination and the considerably high sensitivity of 416.4 mV mm−1. This sensitivity is much larger than the values in other reported MoS2-based devices. Comparatively, the LPE in the MoS2/p-GaAs heterojunction is much weaker. The mechanisms to the LPE are unveiled by constructing the energy-band alignment of the MoS2/GaAs heterojunctions. The excellent LPE characteristics make MoS2 films combined with GaAs semiconductors promising candidates for the application of high-performance position-sensitive detectors. MoS2; GaAs; Photovoltaic; Heterojunction; Interface Background Due to its excellent properties, molybdenum disulfide (MoS2) is being investigated as one typical kind of twodimensional materials to develop next-generation microelectronic devices and optoelectronic devices [ 1–5 ]. Unlike graphene, MoS2 has obvious band gap and its band gap decreases with increasing layer numbers [ 6 ]. The presence of the obvious band gap allows the fabrication of the MoS2 transistors with an on/off ratio exceeding 108 and the photodetectors with high responsivity [ 7, 8 ]. Recently, MoS2 combined with other semiconductors has attracted much interest, such as GaAs, Si, and GaN [ 9–13 ]. These designed heterostructures supply feasible technical route for MoS2-based materials to develop practically applicable optoelectronic devices. Among all these bulk semiconductors, GaAs has a suitable direct band gap of ~ 1.42 eV and high electron mobility (~ 8000 cm2 V−1 s−1). Lin et al. fabricated MoS2/ GaAs solar cells with a power conversion efficiency over 9.03% [9]. Further, Xu et al. reported a MoS2/ GaAs self-driven photodetector with the extremely high detectivity of 3.5 × 1013 Jones [ 10 ]. In previous reports, the studies on MoS2/GaAs heterostructures have been mainly focused on the application in the area of solar cells and photodetectors. However, the MoS2/GaAs as a position-sensitive detector (PSD) based on the lateral photovoltaic effect (LPE) has been reported rarely. Different from the ordinary longitudinal photovoltaic effect, the LPE originates from the lateral diffusion and recombination of the photongenerated carriers in the inversion layer at the interface [ 14–18 ]. In the LPE effect, a lateral photovoltage (LPV) can be obtained and it changes linearly with the laser spot position on the active region of the device surface. These characteristics make LPE very useful in developing high-performance PSDs and have been studied widely in the area of robotics, biomedical applications, process control, position information systems, and so on. In this work, MoS2 thin films with different thickness are deposited on the surface of n-/p-GaAs substrates via magnetron sputtering technique. A large LPE is observed in the fabricated MoS2/n-GaAs heterojunction, and the sensitivity reached 416.4 mV mm−1. Our results further show that the LPE exhibits obvious dependence on the carrier types of the GaAs substrates and the thickness of the MoS2 films. Through the construction of the energy-band alignment at the interface, the mechanisms to the LPE in the devices are proposed. Methods MoS2 thin films were deposited on (100)-oriented GaAs substrates using the DC magnetron sputtering technique. The MoS2 powders (purity, ~ 99%) were coldpressed into a disk under the pressure of 20.0 MPa. The as-fabricated disk (Φ60.0 mm × 4.5 mm) was used as the target during sputtering. The n-/p-GaAs substrates were used in our experiments, respectively. Before the deposition, the substrates were ultrasonically cleaned in sequence by alcohol, acetone, and de-ionized water. Subsequently, MoS2 thin films with different thickness (dMoS2 = ~ 10, 30, 50, 90 nm) were grown on the GaAs substrates at the temperature of 400 °C, respectively. During the deposition, the working pressure and power were kept at 1.0 Pa and 10.0 W, respectively. As a reference, MoS2 thin films were also deposited on intrinsic GaAs (i-GaAs) substrates under the same condition. Finally, about 300-μm In pads with a diameter of 0.5 mm as electrodes were pressed on the MoS2 film. The MoS2 films were characterized using R (...truncated)


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Lanzhong Hao, Yunjie Liu, Zhide Han, Zhijie Xu, Jun Zhu. Large Lateral Photovoltaic Effect in MoS2/GaAs Heterojunction, Nanoscale Research Letters, 2017, pp. 562, Volume 12, Issue 1, DOI: 10.1186/s11671-017-2334-z