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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

The schematic slab hybrid structure of the graphene/GaN (Left Panel) and the calculated total density of states (DOS) for bare GaN and graphene/GaN hybrid structure (Right Panel).Significant change in DOS can be seen in the GaN band gap (~3.495 eV) energy region before and after the graphene covering.
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f5: The schematic slab hybrid structure of the graphene/GaN (Left Panel) and the calculated total density of states (DOS) for bare GaN and graphene/GaN hybrid structure (Right Panel).Significant change in DOS can be seen in the GaN band gap (~3.495 eV) energy region before and after the graphene covering.

Mentions: At last, the first-principles simulations on electronic structures of bare GaN and graphene/GaN heterostructure were performed by using the pseudopotential-based code VASP within the Perdew-Burke-Ernzerhof generalized gradient approximation2627, where we use a substrate GaN supercell of size 2 × 2 × 8. Throughout the theoretical calculations, a 400 eV cutoff in the plane wave expansion and a 6 × 6 × 1 Gamma k grid are chosen to ensure the calculation with an accuracy of 10−5 eV. The lattice constants are taken from the experimental values, while the internal atomic positions are optimized until the largest force on each atom was 0.005 eV/Å. As shown in the left panel of Fig. 5, the carbon atoms of graphene couple tightly with the outermost layer of nitrogen atoms so that finite electron transfer may occur in between graphene and GaN. The right panel of Fig. 5 depicts the calculated total density of states (DOS) of bare GaN and graphene/GaN hybrid structure, respectively. Clearly, a significant change in total DOS can be seen before and after graphene contacting with GaN, especially in the free exciton (~3.495 eV) luminescence region. The value of charges transferred from graphene to substrate GaN is estimated to be 0.02e per carbon atom. Our theoretical results show good agreement with experiment and confirm the picture of free exciton dissociation and transfer of liberated electrons.


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)

The schematic slab hybrid structure of the graphene/GaN (Left Panel) and the calculated total density of states (DOS) for bare GaN and graphene/GaN hybrid structure (Right Panel).Significant change in DOS can be seen in the GaN band gap (~3.495 eV) energy region before and after the graphene covering.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f5: The schematic slab hybrid structure of the graphene/GaN (Left Panel) and the calculated total density of states (DOS) for bare GaN and graphene/GaN hybrid structure (Right Panel).Significant change in DOS can be seen in the GaN band gap (~3.495 eV) energy region before and after the graphene covering.
Mentions: At last, the first-principles simulations on electronic structures of bare GaN and graphene/GaN heterostructure were performed by using the pseudopotential-based code VASP within the Perdew-Burke-Ernzerhof generalized gradient approximation2627, where we use a substrate GaN supercell of size 2 × 2 × 8. Throughout the theoretical calculations, a 400 eV cutoff in the plane wave expansion and a 6 × 6 × 1 Gamma k grid are chosen to ensure the calculation with an accuracy of 10−5 eV. The lattice constants are taken from the experimental values, while the internal atomic positions are optimized until the largest force on each atom was 0.005 eV/Å. As shown in the left panel of Fig. 5, the carbon atoms of graphene couple tightly with the outermost layer of nitrogen atoms so that finite electron transfer may occur in between graphene and GaN. The right panel of Fig. 5 depicts the calculated total density of states (DOS) of bare GaN and graphene/GaN hybrid structure, respectively. Clearly, a significant change in total DOS can be seen before and after graphene contacting with GaN, especially in the free exciton (~3.495 eV) luminescence region. The value of charges transferred from graphene to substrate GaN is estimated to be 0.02e per carbon atom. Our theoretical results show good agreement with experiment and confirm the picture of free exciton dissociation and transfer of liberated electrons.

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