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Luminescence signature of free exciton dissociation and liberated electron transfer across the junction of graphene/GaN hybrid structure.

Wang J, Zheng C, Ning J, Zhang L, Li W, Ni Z, Chen Y, Wang J, Xu S - Sci Rep (2015)

Bottom Line: By comparing the near-band-edge excitonic emissions before and after the graphene covering, some structures in the excitonic PL spectra are found to show interesting changes.In particular, a distinct "dip" structure is found to develop at the center of the free exciton emission peak as the temperature goes up.First-principles simulations provide clear evidence of finite electron transfer at the interface between graphene and GaN.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, HKU-Shenzhen Institute of Research and Innovation (HKU-SIRI), HKU-CAS Joint Laboratory on New Materials, The University of Hong Kong, Pokfulam Road, Hong Kong, China.

ABSTRACT
Large-area graphene grown on Cu foil with chemical vapor deposition was transferred onto intentionally undoped GaN epilayer to form a graphene/GaN Schottky junction. Optical spectroscopic techniques including steady-state and time-resolved photoluminescence (PL) were employed to investigate the electron transfer between graphene and n-type GaN at different temperatures. By comparing the near-band-edge excitonic emissions before and after the graphene covering, some structures in the excitonic PL spectra are found to show interesting changes. In particular, a distinct "dip" structure is found to develop at the center of the free exciton emission peak as the temperature goes up. A mechanism that the first dissociation of some freely moveable excitons at the interface was followed by transfer of liberated electrons over the junction barrier is proposed to interpret the appearance and development of the "dip" structure. The formation and evolution process of this "dip" structure can be well resolved from the measured time-resolved PL spectra. First-principles simulations provide clear evidence of finite electron transfer at the interface between graphene and GaN.

No MeSH data available.


Related in: MedlinePlus

Schematic drawings of energy band structures of graphene and n-type GaN before (a) and after the contacting (b). Temperature-dependent PL spectra of the as-grown GaN (black solid line) and graphene/GaN (red solid line) are depicted in semi-logarithmic scale (c). All spectra are normalized at DX peak intensity. DX, Ix, FXA, and FXB lines can be well resolved and indicated by different color vertical arrows.
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f2: Schematic drawings of energy band structures of graphene and n-type GaN before (a) and after the contacting (b). Temperature-dependent PL spectra of the as-grown GaN (black solid line) and graphene/GaN (red solid line) are depicted in semi-logarithmic scale (c). All spectra are normalized at DX peak intensity. DX, Ix, FXA, and FXB lines can be well resolved and indicated by different color vertical arrows.

Mentions: For graphene/GaN contacts, usually a Schottky junction forms due to van der Waals attraction and electron transfer6141517. Fig. 2(a) and (b) show schematic drawings of band structures of graphene and n-type GaN before and after their contacting, respectively. qφg is the work function of graphene (~4.9 eV for CVD sample), χe is the electron affinity of GaN (~4.1 eV), qφSBH ≈ 0.74 eV is Schottky barrier height of graphene/GaN junction14. Vbi is the built-in voltage. Eg is the band gap of GaN and Ef is the Fermi energy of GaN. As mentioned earlier, the electrical properties of graphene/GaN contact have been addressed previously. In the present work, we concentrate on its optical properties, especially luminescence signatures of free exciton dissociation at the interface and transfer of liberated electrons over the junction.


Luminescence signature of free exciton dissociation and liberated electron transfer across the junction of graphene/GaN hybrid structure.

Wang J, Zheng C, Ning J, Zhang L, Li W, Ni Z, Chen Y, Wang J, Xu S - Sci Rep (2015)

Schematic drawings of energy band structures of graphene and n-type GaN before (a) and after the contacting (b). Temperature-dependent PL spectra of the as-grown GaN (black solid line) and graphene/GaN (red solid line) are depicted in semi-logarithmic scale (c). All spectra are normalized at DX peak intensity. DX, Ix, FXA, and FXB lines can be well resolved and indicated by different color vertical arrows.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4286737&req=5

f2: Schematic drawings of energy band structures of graphene and n-type GaN before (a) and after the contacting (b). Temperature-dependent PL spectra of the as-grown GaN (black solid line) and graphene/GaN (red solid line) are depicted in semi-logarithmic scale (c). All spectra are normalized at DX peak intensity. DX, Ix, FXA, and FXB lines can be well resolved and indicated by different color vertical arrows.
Mentions: For graphene/GaN contacts, usually a Schottky junction forms due to van der Waals attraction and electron transfer6141517. Fig. 2(a) and (b) show schematic drawings of band structures of graphene and n-type GaN before and after their contacting, respectively. qφg is the work function of graphene (~4.9 eV for CVD sample), χe is the electron affinity of GaN (~4.1 eV), qφSBH ≈ 0.74 eV is Schottky barrier height of graphene/GaN junction14. Vbi is the built-in voltage. Eg is the band gap of GaN and Ef is the Fermi energy of GaN. As mentioned earlier, the electrical properties of graphene/GaN contact have been addressed previously. In the present work, we concentrate on its optical properties, especially luminescence signatures of free exciton dissociation at the interface and transfer of liberated electrons over the junction.

Bottom Line: By comparing the near-band-edge excitonic emissions before and after the graphene covering, some structures in the excitonic PL spectra are found to show interesting changes.In particular, a distinct "dip" structure is found to develop at the center of the free exciton emission peak as the temperature goes up.First-principles simulations provide clear evidence of finite electron transfer at the interface between graphene and GaN.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, HKU-Shenzhen Institute of Research and Innovation (HKU-SIRI), HKU-CAS Joint Laboratory on New Materials, The University of Hong Kong, Pokfulam Road, Hong Kong, China.

ABSTRACT
Large-area graphene grown on Cu foil with chemical vapor deposition was transferred onto intentionally undoped GaN epilayer to form a graphene/GaN Schottky junction. Optical spectroscopic techniques including steady-state and time-resolved photoluminescence (PL) were employed to investigate the electron transfer between graphene and n-type GaN at different temperatures. By comparing the near-band-edge excitonic emissions before and after the graphene covering, some structures in the excitonic PL spectra are found to show interesting changes. In particular, a distinct "dip" structure is found to develop at the center of the free exciton emission peak as the temperature goes up. A mechanism that the first dissociation of some freely moveable excitons at the interface was followed by transfer of liberated electrons over the junction barrier is proposed to interpret the appearance and development of the "dip" structure. The formation and evolution process of this "dip" structure can be well resolved from the measured time-resolved PL spectra. First-principles simulations provide clear evidence of finite electron transfer at the interface between graphene and GaN.

No MeSH data available.


Related in: MedlinePlus