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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

Temperature-dependent PL spectra of the as-grown GaN (black) and graphene/GaN hybrid structure (red) from 77 K to 200 K.Dashed blue and magenta lines align with the centers of FXA and FXB bands, respectively.
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f3: Temperature-dependent PL spectra of the as-grown GaN (black) and graphene/GaN hybrid structure (red) from 77 K to 200 K.Dashed blue and magenta lines align with the centers of FXA and FXB bands, respectively.

Mentions: In addition to the significant reduction and quick thermal quenching of Ix line, more interesting behavior was observed for free exciton emissions. As can be seen from Fig. 2(c) and Fig. 3, free exciton A (FXA) bands of the two samples behave very differently as the temperature increases. For the as-grown GaN epilayer, FXA peak gradually becomes dominant due to thermal liberation of bound excitons into free excitons as previously observed24. Its lineshape keeps unchanged except broadening due to phonon scattering effect. As for the graphene/GaN hybrid structure, however, the lineshape of the FXA peak shows a remarkable change when temperature is beyond 30 K. A dip at peak center develops and becomes noticeable for temperatures above 77 K. Furthermore, free exciton B (FXB) emission band also exhibits similar behavior although its intensity is relatively much weaker. These results reveal that the graphene capping layer has a strong influence on free excitons in the GaN underlying layer.


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)

Temperature-dependent PL spectra of the as-grown GaN (black) and graphene/GaN hybrid structure (red) from 77 K to 200 K.Dashed blue and magenta lines align with the centers of FXA and FXB bands, respectively.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f3: Temperature-dependent PL spectra of the as-grown GaN (black) and graphene/GaN hybrid structure (red) from 77 K to 200 K.Dashed blue and magenta lines align with the centers of FXA and FXB bands, respectively.
Mentions: In addition to the significant reduction and quick thermal quenching of Ix line, more interesting behavior was observed for free exciton emissions. As can be seen from Fig. 2(c) and Fig. 3, free exciton A (FXA) bands of the two samples behave very differently as the temperature increases. For the as-grown GaN epilayer, FXA peak gradually becomes dominant due to thermal liberation of bound excitons into free excitons as previously observed24. Its lineshape keeps unchanged except broadening due to phonon scattering effect. As for the graphene/GaN hybrid structure, however, the lineshape of the FXA peak shows a remarkable change when temperature is beyond 30 K. A dip at peak center develops and becomes noticeable for temperatures above 77 K. Furthermore, free exciton B (FXB) emission band also exhibits similar behavior although its intensity is relatively much weaker. These results reveal that the graphene capping layer has a strong influence on free excitons in the GaN underlying layer.

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