Photonic and Electronic Characterization of Two-dimensional Transition Metal Dichalcogenides

Abde Mayeen Shafi

Research output: ThesisDoctoral ThesisCollection of Articles


Two-dimensional (2D) transition metal dichalcogenides (TMDCs) hold promise for numerous unprecedented applications in nanophotonics, optoelectronics, and nanoelectronics, owing to their extraordinary electrical and optical properties. However, these materials still face several challenges, including limited light-matter interactions, low luminescent yield, reduced carrier mobility, and susceptibility to environmental changes. This thesis aims to address the aforementioned limitations by employing various advanced techniques to enhance the optical and electronic properties of these materials. In this thesis, the light-matter interaction in TMDCs is enhanced by realizing mixed-dimensional heterostructures. High-performance photonic and optoelectronic devices are constructed by investigating two distinct types of these heterostructures. Firstly, monolayer MoS2 is transferred onto AlGaAs nanowires to create a mixed-dimensional heterostructure. A significant enhancement in Raman and photoluminescence responses is achieved from the heterostructure attributed to the electromagnetic field confinement within the high refractive index nanowire. The heterostructure also exhibits optical anisotropy due to the 3-fold rotational symmetry breaking of MoS2 caused by the nanowire. Additionally, the fabricated phototransistor using this heterostructure demonstrates improved responsivity and detectivity. Secondly, another mixed-dimensional heterostructure is formed by epitaxially growing InP nanowires directly on MoS2. High-density nanowire growth is achieved while ensuring the stability of MoS2. This heterostructure generates strong second- and third-harmonic signals and, notably, 5th and 7th-order high-harmonic signals, opening up potential applications such as lasers and electro-optic modulators. In the subsequent part of the thesis, the electronic properties of TMDCs are investigated and tuned to fabricate high-performance electronic and optoelectronic devices. At first, the impact of high temperatures on multilayer MoTe2 field-effect transistors is systematically explored to determine the optimal annealing temperature for the devices and acquire a deeper understanding of the surface oxidation-mediated defect formation and hopping transport mechanism in MoTe2 devices. Furthermore, a straightforward technique is proposed that involves substrate engineering and Al2O3 passivation to enhance the performance of few-layer MoTe2 devices by introducing local tensile strain and reducing electron-phonon scattering in the channel. This results in significant improvements in carrier mobility and device quality. Lastly, a simple optical writing technique is employed to transform the semiconducting 2H phase of MoTe2 into the metallic 1T´ phase, resulting in improved third harmonic generation signals and the performance of optoelectronic devices. These findings show great promise for advancing integrated photonic and optoelectronic circuits based on 2D-TMDCs.
Translated title of the contributionPhotonic and Electronic Characterization of Two-dimensional Transition Metal Dichalcogenides
Original languageEnglish
QualificationDoctor's degree
Awarding Institution
  • Aalto University
  • Lipsanen, Harri, Supervising Professor
  • Mackenzie, David, Thesis Advisor
Print ISBNs978-952-64-1589-5
Electronic ISBNs978-952-64-1590-1
Publication statusPublished - 2023
MoE publication typeG5 Doctoral dissertation (article)


  • two-dimensional materials
  • transition metal dichalcogenides
  • mixed-dimensional heterostructures
  • photoluminescence
  • harmonic generations
  • field effect transistors


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