Efficient charge transfer induced organic/inorganic based hybrid heterojunction of Ppy/GaN nanorods for high-performance self-powered UV photodetection

1. Efficient charge transfer induced organic/inorganic
based hybrid heterojunction of Ppy/GaN nanorods for
high performance self-powered UV photodetection
15-01-2021
Presented by
P. Kedhareswara Sairam, Prof. Moon-Deock Kim*
Department of Physics, Chungnam National University, South Korea.

2. Contents
I. Introduction
II. Motivation
III.Experiments
IV.Results and discussions
IV. Conclusions

3. I. Introduction
Self powered-Photodetectors:
 Basically also called photosensor, are sensors of light or other electromagnetic radiation. Typically,
the photo detector that converts optical signals (photons) into electrical signals (current/voltage).
 Self-powered can be described as the device which can be operate without any external power source (0
bias).
UV photodetection

4. Material properties GaN
Structure Wurtzite
Lattice constant (Å) a = 3.18 c = 5.18
Band gap Direct (3.4 eV)
Dielectric constant 10.4
Thermal conductivity
(cm2 /V-s)
2000
Saturation velocity (107 cm/s) 2.5
I. Introduction
GaN
 Issues with pristine GaN nanostructures:
The surface states, poor carrier life, and other native defects in GaN nanorods (NRs) limit their
utilization in high-speed and large-gain ultraviolet (UV) photodetection applications.
 Strategies to improve GaN nanostructures to improve UV photodetection:
GaN PDs designed with a Schottky junction, p-n junction organic –inorganic and p-i-n.

5. I. Introduction
Polypyrrole (Ppy)
 A typical organic polymer.
 Polypyrrole (Ppy) is one of the typical p-type intrinsic
conductive polymer with a strong interactive possible cross
linking chains which helps to maintain a healthy bonding to the
other compounds which includes high environmental stability
and possess high electrical conductivity.

6. II. Motivation
 GaN nanorods were functionalized with Ppy. The amine functional groups present in
Ppy can effectively passivate the surface states in GaN nanorods.
 Thereby, p-n junction will form in the hybrid heterojunction.
 The effect of passivation showed a significant influence on optical, electrical, structural
properties on GaN nanorods PD.
 Thereby, the charge transformation would exists in between the heterojunction that it
could generate a built-in-potential at the interface, which further offers the self-driving
force to move the photo-generated carriers across the junction without external power
supply.
 Thus, it can effectively enhances the optoelectrical properties of the device [1].
[1] N. Prakash. et.al, Appl. Phys. Lett. 109, 242102 (2016).

7. III. Experiments
Growth
• Plasma-assisted molecular beam epitaxy
• GaN nanorods on /Si(111)
Device fabrication
• Ppy was spin coated with speed of 3000
rpm on patterned GaN NRS followed by
organic cleaning.
Metal deposition
• Electron beam evaporation
• Top(Au:100 nm)-bottom(In) contact
Characterizations
• SEM, FTIR, XPS, UV-Visible
spectroscopy, characterizations and I-V,
and Photodetection properties.

8. IV. Results and discussions
SEM UV-Visible FTIR
[2] S. Nongthombam.et.al, J. VLSI DCS (2020), pp. 171-175.
[3] S. Munusamy.et.al, Arab. J. Chem (2019) 12, 3565-3575
 The cross sectional SEM image of the Ppy/GaN NRs hybrid device,.
 The characteristic absorption peaks of UV-Visible spectra positioned at 275 nm and a weak peak at 420
nm endorse the presence of Ppy and the optical band gap of Ppy was estimated as 3.1 eV from Tauc
plot (inset figure) [2, 3].
 The band at 557 cm-1 (C-N) and others evaluates the existence of related functional groups and their
vibrational bands in Ppy and the peak at 669 cm-1 corresponds to Ga-O that confirms the successful
deposition of Ppy into the GaN [2].
1.2 1.8 2.4 3.0 3.6 4.2 4.8
Ppy
(h)
2
(eV/cm)
2
h (eV)
3.1eV

9. IV. Results and discuss
XPS
[3] S. Munusamy.et.al, Arab. J. Chem (2019) 12, 3565-3575.

10. IV. Results and discuss
∆Ev = E 𝐶1𝑠
𝑃1
− EVBM
𝑃1
+ (EGa2p3
2
𝑃1/GaN
−E 𝐶1𝑠
𝑃1/GaN
) − (EGa2p3
2
GaN
−EVBM
GaN
) (1)
∆Ec = ∆Ev + Eg 𝑃1 − Eg GaN (2)
XPS-band offsets
[4] E. A. Kraut.et.al, Phys. Rev. Lett., (1980), 44, 1620-1623.

11. IV. Results and discuss
I-V and photocurrent measurements

12. IV. Results and discuss
(a) (b)
Photoresponse properties
𝑅 𝜆 =
∆𝐼
𝐴∗𝑃
−−−−− −(3)
𝐷∗
=
𝐴
1
2 𝑅 𝜆
2𝑒𝐼 𝑑
−−−− −(4)
𝐸𝑄𝐸 =
ℎ𝑐
𝑒𝜆
𝑅 𝜆 −−− −(5)
 The estimated detectivity, responsivity and EQE by using the above standard formula, under 382 nm (1.32 mW/cm2) were
found in the range of5.0×1012 Jones, 102 A/W and 29.8×103 (%), and 25.×106 % respectively.
 The Rλ and EQE of hybrid device was found to be decreased with increasing the power densities varying from 1.32
mW/cm2 to 6.56 mW/cm2, were ascribed to the carriers (mainly holes) trapping saturation resulting in larger quantum
efficiency [1, 5].
[1] N. Prakash. et.al, Appl. Phys. Lett. 109, 242102 (2016).
[5] N. Prakash. et.al, Adv. Optical Mater. (2018), 6, 1800191.

13. IV. Results and discuss
Band diagram
 On UV absorption the hybrid PD stimulates the electrons from valence band to the conduction band in GaN and highest
occupied molecular orbit (HOMO) to lowest unoccupied molecular orbit (LUMO) in Ppy to produce excitons and can
diffused through the depletion region formed at interface [5].
 As a result of built-in-potential at the interface, the excitons were being separated into the free holes and electrons
moving towards the p-Ppy and n-GaN layers respectively, resulting to the high photodetector properties at zero bias.
[5] N. Prakash. et.al, Adv. Optical Mater. (2018), 6, 1800191.

14. V. Conclusion
 Self-powered UV photodetection optoelectrical properties of the Ppy/GaN nanorods hybrid
device was successfully investigated.
 The surface trap states of the pristine GaN nanorods were effective passivated by the
amine functional groups of Ppy.
 The charge transformation between the p-n junction interface of hybrid device would be the
reason for the excellent photo current properties.
 Under UV light, the hybrid device exhibited the high photocurrent properties as compared to
the pristine device.
 The high photoresponse characteristics was due to the formation of built-in potential at the
interface junction, that it would helps to separating the generated holes and electrons
moving towards the p-Ppy and n-GaN layers respectively, resulting to the high
photodetector properties at zero bias.

15. Thank You
Prof. Moon-Deock
Kim
Byung-Guon
Park
Dr. M. ReddeppaP. Kedhareswara
Sairam