1S.S.H

2

Outline

• Introduction• Experiments• Results and Discussion• Conclusion• References

3

Introduction• Two-dimensional Graphene has attracted considerable attention

recently due to its unique properties such as

① high carrier mobility ~ (15000 )

② broad spectral absorption

③ low optical absorption rate ~(2.3%)

④ short carrier lifetime

⑤ Small band gap ~ (0ev~0.25ev)

⑥ ultrafast response time ~ (1.5 ps)

⑦ as well as mechanical flexibility.

4

Introduction• The heterojunctions of graphene with traditional semiconductor

materials can be used to construct various functional devices, such as :

① With Si to produce diodes

② Photodetectors

③ So-called “barristor;” with monolayer MoS2 and WS2 to form vertical field effect transistors

④ With ZnO nanowire to fabricate UV detectors

5

Introduction• In this work, we report the graphene/GaN diodes for UV and

visible photodetectors with large photoresponsive area. The physical mechanisms are discussed by considering the variation of the Schottky barrier at the graphene/GaN interface with photo-illumination.

6

Experiments

100nm thick

FIG. 1. (a) Schematic diagram of the device structure. (b) Optical image of a typical device.

7

Results and Discussion

FIG. 1. (c) Photoluminescence spectrum of the GaN film. (d) Ramanspectrum of the single layer graphene.

Source1: He–Cd laser~ (325nm)

Source2: Green laser~ (514nm)

Spot size: ~ (2μm)

361 nm

8

Results and DiscussionSource: 325nm UV laser

100100% laser power

(log

) Current on/off ratio

10V and -10

I (light) / I (dark) → 56 and 1820

9

Results and Discussion

接觸面積

理查德森常數GaN

Shocktty Barrier hightIn Dark = 0.49ev

Elementary charge (q) = 1.60217733 C Boltzmann constant (k) = 1.380658 10-23 J/T Electro affinity of GaN is 4.1ev Work function of grapgene is 4.6ev

n：理想因子 (ideality factor)

10

Results and DiscussionSource: 514nm Green laser

Current on/off ratio Under reverse bias

I (light) / I (dark) →

11

Results and Discussion

Power law =

12

Results and Discussion

FIG. 5. Multi-cycle photocurrent response to incident (a) UV and (b) green light under bias voltage of 10 V. Photoelectric responses by chopping light with (c) 800 Hz for UV light and (d) 100 Hz for green light.

13

Results and Discussion

The extraction of the rising and decay time constants for (e) UV light and (f) green light.

14

Results and Discussion

Fowler 發射係數

2.62 (ev) 光子能量

15

Conclusion• The barrier height can be effectively tuned by incident UV laser

with different light powers, and thus the photoconductance is changed accordingly.

• The devices show a photoelectric response with millisecond rising and decaying time constants, paving an alternative route towards broadband photodetectors with large photoresponsive area.

16

References• Layer-by-layer assembly of vertically conducting graphene devices (Jing-

Jing Chen,Jie Meng,Yang-Bo Zhou,Han-Chun Wu,Ya-Qing Bie,Zhi-Min Liao&Da-Peng Yu

• Graphene Barristor, a Triode Device with a Gate-Controlled Schottky Barrier, Heejun Yang, Jinseong Heo, Seongjun Park,1 Hyun Jae Song, David H. Seo, Kyung-Eun Byun, Philip Kim, InKyeong Yoo, Hyun-Jong Chung, Kinam Kim

17

Thank you for your attention