Highenergy photoemission studies on InN

1
High-energy photoemission studies on InN
H. Makino1, P.P. Chen2, J.J. Kim1, T. Yao1,2, A.
Yamamoto3, T. Matsuoka4, E. Ikenaga5, Y.
Nishino6, D. Miwa6, K. Tamasaku6, M. Yabashi5, T.
Ishikawa6, A. Takeuchi5, M. Awaji5, K.
Kobayashi5, and T. Yamamoto7 1. Institute for
Materials Research, Tohoku University, Sendai 2.
Center for Interdisciplinary Research, Tohoku
University, Sendai 3. Department of E E, Fukui
University, Fukui 4. T. Matsuoka, NTT Basic
Research Labs, Atsugi 5. JASRI/SPring-8, Hyogo
679-5198 6. RIKEN/SPring-8, Hyogo 7. Department
of E and Photonics, Kochi University of
Technology, Kochi
2
Hard X-ray photoemission spectroscopy
Bulk sensitive electronic structure
Experimental conditions at BL29XU in SPring-8 ?
excitation energy 6 - 10 keV, DE (hn) 60meV _at_ 6
keVV ? photon flux 2x1011 photons/sec _at_ 100x 60
mm2 ? analyzer R4000-10kV (Gammadata Scienta) ?
vacuum 10-510-6 and 10-10 Torr for R.T. and LT
meas. ? No surface treatment for present samples
DE(total) 310 meV_at_RT
14/45
3
High-energy XPS measurements
Au plate (HEXPS) Au film (UPS)
Y. Takata et al. Appl. Phys. Lett. 84, 4310 (04)
4
Optical absorption vs carrier concentration

• Eg determined by a2 vs hn)
• A 6.31020 (cm-3) 1.8 eV
• B 3.61020 (cm-3) 1.4 eV
• C 1.21020 (cm-3) 1.2 eV

J. Wu et al. App. Phys. Lett. 84, 2805 (2004)
5
Burstein-Moss shift of the absorption edge
High carrier conc
Scenario Oxygen incorporated in InN films
Donor ?
Change the optical absorption edge
Low carrier conc
Questions Can XPS detect the metallic states?
Can all the phenomena about the band
structure of InN can be explained?
DOS
E
EF
6
Valence band XPS of InN


0.27
A
Valence
B
C
0.18
Intensity (arb. units)


0.09
Increase in carrier conc 1.Increase in DOS of
metallic state 2. Increase in shift of EF 3.
Increase in oxygen signal (O 1s)
0.00
2
1
0
1
2
10
8
6
4
2
0
2
Binding energy (eV)
Binding energy (eV)


Fermi level --- VBM A 2.0 eV (6.3x1020
cm-3) B 1.6 eV (3.6x1020 cm-3) C
1.3 eV (1.2x1020 cm-3)
Optical gap 1.8 eV 1.4 eV
1.2 eV
Fair agreement
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Calculated total DOS for InN and In36N35O1
ON enhances DOS of conduction band.
8
Valence band XPS of InN

• Electronic States above VBM are detected.
• Oxygen contamination
• a. increase in DOS around 2 eV
• b. decrease in DOS around 5 eV

(For comparison VBM is aligned)
9
Electronic states above VBM
Integrated intensity of metallic states
Eg increases

• Two electronic states are detected
• Conduction band filling (B-M effect)
• Acceptor-like states

10
Valence band XPS of InN

• States above VBM are observed.
• Oxygen contamination
• a. increase in DOS around 2 eV
• b. decrease in DOS around 5 eV

(For comparison VBM is aligned)
11
Calculated total DOS for InN and In36N35O1
In-O bonding pushes the N 2p states to higher
energy side, which may give rise to an increase
in DOS at around VBM and decrease at VBB.
However, What about the effect of In2O3? ?
another possible cause of the change in
DOS. (Dr SH Wei)
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Conclusions

• 1. Metallic states due to oxygen donors are
  detected by HEXPS,
• The metallic states can be explained in
  terms of Burstein-Moss effect.
• Acceptor-like states above VBM are detected.
• Three oxygen bonding states due to ON, the
  acceptor-like states(?), and In2O3 most likely
  at surface(?).
• Oxygen contamination makes DOS of VBM enhanced
  and DOS of VBB reduced, due to In-O bonding
  and/or In2O3 bonding.
• Acknowledgements Fruitful discussion with Dr
  Su-Huai Wei (NREL) in particular on DOS of InN
  contaminated with O is greatly appreciated.