Abstract

Excitation power and energy dependent photoluminescence (PL) and transient absorption spectroscopy (TAS) studies are carried out on chemical vapour deposition (CVD) grown 1L-MoS₂ films to understand the process of trion formation. The study shows that excitation with sufficiently low photon energy results in the creation of trions directly in the K/K′ valleys through photon absorption followed by phonon scattering events. On the other hand, excitation energy sufficiently larger than the band gap can generate carriers away from the K/K′ valleys. Dissimilarity in the rates of relaxation of the photo-excited electrons and holes to the bottom of the K/K′ valleys results in the transformation of the excitons residing there into trions. TAS demonstrates a temporary increase of the trion population in the K/K′ valleys. Excitation intensity dependent PL under above-band-gap excitation also suggests coexistence of both trion-generation pathways. This conclusion is further validated by a rate equation model.

Abstract

Excitation power and energy dependent photoluminescence (PL) and transient absorption spectroscopy (TAS) studies are carried out on chemical vapour deposition (CVD) grown 1L-MoS₂ films to understand the process of trion formation. The study shows that excitation with sufficiently low photon energy results in the creation of trions directly in the K/K′ valleys through photon absorption followed by phonon scattering events. On the other hand, excitation energy sufficiently larger than the band gap can generate carriers away from the K/K′ valleys. Dissimilarity in the rates of relaxation of the photo-excited electrons and holes to the bottom of the K/K′ valleys results in the transformation of the excitons residing there into trions. TAS demonstrates a temporary increase of the trion population in the K/K′ valleys. Excitation intensity dependent PL under above-band-gap excitation also suggests coexistence of both trion-generation pathways. This conclusion is further validated by a rate equation model.

Abstract

Excitation power and energy dependent photoluminescence (PL) and transient absorption spectroscopy (TAS) studies are carried out on chemical vapour deposition (CVD) grown 1L-MoS₂ films to understand the process of trion formation. The study shows that excitation with sufficiently low photon energy results in the creation of trions directly in the K/K′ valleys through photon absorption followed by phonon scattering events. On the other hand, excitation energy sufficiently larger than the band gap can generate carriers away from the K/K′ valleys. Dissimilarity in the rates of relaxation of the photo-excited electrons and holes to the bottom of the K/K′ valleys results in the transformation of the excitons residing there into trions. TAS demonstrates a temporary increase of the trion population in the K/K′ valleys. Excitation intensity dependent PL under above-band-gap excitation also suggests coexistence of both trion-generation pathways. This conclusion is further validated by a rate equation model.

Abstract

Excitation power and energy dependent photoluminescence (PL) and transient absorption spectroscopy (TAS) studies are carried out on chemical vapour deposition (CVD) grown 1L-MoS₂ films to understand the process of trion formation. The study shows that excitation with sufficiently low photon energy results in the creation of trions directly in the K/K′ valleys through photon absorption followed by phonon scattering events. On the other hand, excitation energy sufficiently larger than the band gap can generate carriers away from the K/K′ valleys. Dissimilarity in the rates of relaxation of the photo-excited electrons and holes to the bottom of the K/K′ valleys results in the transformation of the excitons residing there into trions. TAS demonstrates a temporary increase of the trion population in the K/K′ valleys. Excitation intensity dependent PL under above-band-gap excitation also suggests coexistence of both trion-generation pathways. This conclusion is further validated by a rate equation model.