Fast, broadband and self-driven photodetectors based on Pt or Pd-TMDs

Abstract

Two-dimensional (2D) materials have sparked intensive research interests worldwide due to their attractive chemical and physical properties, that show great potential for electronic and optoelectronic applications. Graphene, as a first discovered and the thinnest 2D material possesses ultrahigh carrier mobility, but its gapless nature is not suitable for some applications. Transition metal dichalcogenides (TMDs) with tunable bandgap, high carrier mobility and outstanding optical properties, have emerged as new members of 2D materials family, which have been considered as excellent potential candidates for optoelectronic devices. In spite of continued achievements in optoelectronic systems based on group-6 TMDs over the past decade, the fabrication of optoelectronics devices based on narrow bandgap noble metal dichalcogenides such as PtSe2 and PdSe2 still remains in uncharted waters so far. Here, in this thesis, I firstly demonstrate the large-area, uniform and transferable platinum diselenide (PtSe2) films with semiconducting characteristics can be successfully synthesized on various substrates via a simple selenization method. The combination of the produced PtSe2 films with planar GaAs substrate leads to highly sensitive heterojunction photodetectors in the deep ultraviolet-visible to near infrared region. The as-assembled PtSe2/GaAs heterojunction detectors show the peak sensitivity from 650 to 810 nm, with high responsivity, large specific detectivity and fast response speed. Based on first-principle density functional theory, such broad photoresponse ranging from visible to near infrared region is correlated with the semiconducting properties of PtSe2, which has interstitial Se atoms within PtSe2 layers. Secondly, palladium diselenide (PdSe2), another newly discover member of Group-10 TMD, is investigated experimentally and theoretically. By choosing different thickness of precursor Pd metal layer, the thickness of 1.2-20 nm for 2D PdSe2 can be readily synthesized. With the increase in thickness, obvious redshift in wavenumber is revealed by Raman spectroscopy. Furthermore, the wafer-scale PdSe2 films with widely tunable bandgap exhibits an evolution from semiconductor (monolayer) to semimetal (bulk) based on optical absorption and ultraviolet photoemission spectroscopy analyses, being well consistent with density functional theory calculation. What's more, by integrating 20 nm PdSe2 films with Si substrate results in highly sensitive, fast and broadband photodetector with a high responsivity (300 mA/W) and specific detectivity (≈ 1013 Jones). The introduction of black phosphorus quantum dots with device, the device performance can be further optimized. Finally, the large-area heterojunction detector and image sensor based on PdSe2/perovskite hybrid heterostructure are developed. The overall device performances of demonstration in terms of responsivity, specific detectivity, polarization sensitivity, and response speed are systematically studies. Interestingly, after 2000 cycles of operation, the photocurrent of device exhibits no sign of degradation. Lastly, it is revealed that as-assembled PdSe2-perovskite hybrid heterostructure shows good infrared imaging capability, which can record the designed "P", "O", "L", "Y", and "U" image sequentially produced by 808 nm. In conclusion, we have developed a straightforward method to grow wafer-scale group-10 TMDs like PtSe2 and PdSe2, and fabricated optoelectronic devices based on these materials, which exhibited impressive performance in photodetection application due to their distinct optical and electrical properties. The generality of above results suggests that PtSe2 and PdSe2 are ideal materials for assembly of optoelectronic systems in the future.