Abstract

Heterostructures constructed from graphene and transition metal dichalcogenides have established a new platform for optoelectronic applications. Although massive studies have been done on optical response of the heterostructures in recent years, fundamental questions concerning the dynamical charge transfer and subsequent relaxation are still under debate. Hereby, we combined time-resolved terahertz (THz) spectroscopy along with transient absorption (TA) spectroscopy to revisit the interlayer non-equilibrium carrier dynamics in largely lateral size Gr/MoS₂ heterostructure fabricated with chemical vapor deposition (CVD) method. Our experimental results reveal that, with photon-energy below the A-exciton of MoS₂ monolayer, hot electrons transfer from graphene to MoS₂ takes place in time scale of less than 0.5 ps, resulting in ultrafast formation of interfacial exciton in the heterostructure, subsequently, recombination relaxation of the interfacial exciton occurs in time scale of ~18 ps. A new model considering carrier heating and photogating effect in graphene is proposed to estimate the amount of carrier transfer in the heterostructure, which shows a good agreement with experimental result. Moreover, when the photon-energy is on-resonance with the A-exciton of MoS2, photogenerated holes in MoS₂ are transferred to graphene layer within 0.5 ps, leading to the formation of interfacial exciton, the subsequent photoconductivity (PC) relaxation of graphene and bleaching recovery of A-exciton in MoS₂ take place around ~10 ps time scale, ascribing to the interfacial exciton recombination. The faster recombination time of interfacial exciton with on-resonance excitation could come from the reduced interface barrier caused by bandgap renormalization effect. Our study provides deep insight into the understanding of interfacial charge transfer as well as the relaxation dynamics in graphene-based heterostructures, which are promising for the applications of graphene-based optoelectronic devices.

Abstract

Heterostructures constructed from graphene and transition metal dichalcogenides have established a new platform for optoelectronic applications. Although massive studies have been done on optical response of the heterostructures in recent years, fundamental questions concerning the dynamical charge transfer and subsequent relaxation are still under debate. Hereby, we combined time-resolved terahertz (THz) spectroscopy along with transient absorption (TA) spectroscopy to revisit the interlayer non-equilibrium carrier dynamics in largely lateral size Gr/MoS₂ heterostructure fabricated with chemical vapor deposition (CVD) method. Our experimental results reveal that, with photon-energy below the A-exciton of MoS₂ monolayer, hot electrons transfer from graphene to MoS₂ takes place in time scale of less than 0.5 ps, resulting in ultrafast formation of interfacial exciton in the heterostructure, subsequently, recombination relaxation of the interfacial exciton occurs in time scale of ~18 ps. A new model considering carrier heating and photogating effect in graphene is proposed to estimate the amount of carrier transfer in the heterostructure, which shows a good agreement with experimental result. Moreover, when the photon-energy is on-resonance with the A-exciton of MoS2, photogenerated holes in MoS₂ are transferred to graphene layer within 0.5 ps, leading to the formation of interfacial exciton, the subsequent photoconductivity (PC) relaxation of graphene and bleaching recovery of A-exciton in MoS₂ take place around ~10 ps time scale, ascribing to the interfacial exciton recombination. The faster recombination time of interfacial exciton with on-resonance excitation could come from the reduced interface barrier caused by bandgap renormalization effect. Our study provides deep insight into the understanding of interfacial charge transfer as well as the relaxation dynamics in graphene-based heterostructures, which are promising for the applications of graphene-based optoelectronic devices.

Abstract

Heterostructures constructed from graphene and transition metal dichalcogenides have established a new platform for optoelectronic applications. Although massive studies have been done on optical response of the heterostructures in recent years, fundamental questions concerning the dynamical charge transfer and subsequent relaxation are still under debate. Hereby, we combined time-resolved terahertz (THz) spectroscopy along with transient absorption (TA) spectroscopy to revisit the interlayer non-equilibrium carrier dynamics in largely lateral size Gr/MoS₂ heterostructure fabricated with chemical vapor deposition (CVD) method. Our experimental results reveal that, with photon-energy below the A-exciton of MoS₂ monolayer, hot electrons transfer from graphene to MoS₂ takes place in time scale of less than 0.5 ps, resulting in ultrafast formation of interfacial exciton in the heterostructure, subsequently, recombination relaxation of the interfacial exciton occurs in time scale of ~18 ps. A new model considering carrier heating and photogating effect in graphene is proposed to estimate the amount of carrier transfer in the heterostructure, which shows a good agreement with experimental result. Moreover, when the photon-energy is on-resonance with the A-exciton of MoS2, photogenerated holes in MoS₂ are transferred to graphene layer within 0.5 ps, leading to the formation of interfacial exciton, the subsequent photoconductivity (PC) relaxation of graphene and bleaching recovery of A-exciton in MoS₂ take place around ~10 ps time scale, ascribing to the interfacial exciton recombination. The faster recombination time of interfacial exciton with on-resonance excitation could come from the reduced interface barrier caused by bandgap renormalization effect. Our study provides deep insight into the understanding of interfacial charge transfer as well as the relaxation dynamics in graphene-based heterostructures, which are promising for the applications of graphene-based optoelectronic devices.

Abstract

Heterostructures constructed from graphene and transition metal dichalcogenides have established a new platform for optoelectronic applications. Although massive studies have been done on optical response of the heterostructures in recent years, fundamental questions concerning the dynamical charge transfer and subsequent relaxation are still under debate. Hereby, we combined time-resolved terahertz (THz) spectroscopy along with transient absorption (TA) spectroscopy to revisit the interlayer non-equilibrium carrier dynamics in largely lateral size Gr/MoS₂ heterostructure fabricated with chemical vapor deposition (CVD) method. Our experimental results reveal that, with photon-energy below the A-exciton of MoS₂ monolayer, hot electrons transfer from graphene to MoS₂ takes place in time scale of less than 0.5 ps, resulting in ultrafast formation of interfacial exciton in the heterostructure, subsequently, recombination relaxation of the interfacial exciton occurs in time scale of ~18 ps. A new model considering carrier heating and photogating effect in graphene is proposed to estimate the amount of carrier transfer in the heterostructure, which shows a good agreement with experimental result. Moreover, when the photon-energy is on-resonance with the A-exciton of MoS2, photogenerated holes in MoS₂ are transferred to graphene layer within 0.5 ps, leading to the formation of interfacial exciton, the subsequent photoconductivity (PC) relaxation of graphene and bleaching recovery of A-exciton in MoS₂ take place around ~10 ps time scale, ascribing to the interfacial exciton recombination. The faster recombination time of interfacial exciton with on-resonance excitation could come from the reduced interface barrier caused by bandgap renormalization effect. Our study provides deep insight into the understanding of interfacial charge transfer as well as the relaxation dynamics in graphene-based heterostructures, which are promising for the applications of graphene-based optoelectronic devices.