1. Optical properties of iii-n nanostructures
Andrés Cantarero
University of Valencia
Spain
Optical properties of iii-n nanostructures

2. Valence band
Composing one of the most important facets of Valencia's music scene, both past and present, are its internationally renowned "bandes." Found in every city and village of the Valencian community, these "bandes" are performing brass bands that play an integral part in festivals; in fact, they even have a music festival of their own: the Certamen Internacional de Bandas de Música (International Band Competition). Taking place annually since 1886, thousands of musicians descend upon the city as parts of regional, national, international, civilian and military brass bands.
Banda de Chiva

3. Valencia and its University
Valencia, 138 bce
810,000 p;1,500,000 mr
We have 45,000 students
The University was founded in 1499

4. Outline Interest in nitride semiconductors: applications
Generalities on III-N semiconductors
GaN/AlN self-assembled quantum dots
Growth of GaN/AlN/SiC self-assembled QDs
Optical properties of polar and non polar QDs
Q1D semiconductor nanostructures
InN nanowires
Growth of InN nanowires
Optical properties of InN nanowires
Conclusions

5. Optical storage devices
Sony launches its Blue-ray recorder (Sept 20th, 2006)
54 Gb capacity
400 nm laser
(Nichia Corp)
Prof. Nakamura (UCSB) fabricated a nm laser based on NP InGaN/GaN

6. 1st prize street (ecological) illumination
White LEDs
1st prize street (ecological) illumination
Fallas 2009
Kittilä (Finland) ,

7. Nitride semiconductors

8. Crystal structure
GaN crystallizes in the wurtzite structure under normal conditions
Difference of packing between wurtzite and ZB
Origin of PSP in Ga-face GaN

9. Structural parameters and PSP
But, it is grown on Al2O3, SiC or Si(111)
There is, additionally, PPZ
1010 disl/cm2
F. Bernardini, V. Fiorentini, D. Vanderbilt, PRB 56, R10024 (1997).

10. Growth of GaN/AlN QDs 6H-SiC Modified Stranski-Krastanow mode
dot
AlN [
0001 ] [2 - 1
10]
2nm
Elastic relaxation
C. Adelmann et al APL 81, 3064 (2002); N. Gogneau et al JAP 94, 2254 (2003)

11. PL and electric field
Photoluminescence of different samples growth with different number of periods
(0001) GaN/AlN QWs
F=10 MV/cm
The built in electric field manifests in the optical properties of GaN/AlN heterostructures through the Stark effect
Is there a way to reduce dislocations and Stark effect?
(a): J. M. Llorens, PhD (2006), Univ. Valencia; (b) Salviati et al., J. Phys. Cond. Matt. 16, S115 (2004); (c) Miyamura et al., APL (2002); (d) Kako et al., APL 83, 984 (2003); (e) Widmann et al., APL 83, 7619 (1998).

12. Non polar QDs
a- and m-plane contain the same amount of Ga and N per layer
5 nm
[1-100]
[0001]
HRTEM
[0001]
Plano a
[1120]
AFM
S. Founta et al, APL 86, (2005)
N. Garro et al., APL 87, (2005)

13. V and electric field X Z
C-plane QD
A-plane QD Z X

14. Growing interest in SNWs
Published papers on semiconductor NWs (Web of Sciences)
Comparison of the number of citations on QDs and NWs
Quasi-one dimensional symmetry
Large surface/volume ratio
New possible heterostructures
High quality materials (strain free)
High quality heterointerfaces (larger LM)

15. From QWs to NWs GaN grown on AlN Fixed N flux Ga bilayer conditions
N-rich conditions
Ingredients:
lattice mismatch
(2.5 % Da/a GaN on AlN)
- surface energy (Ga bilayer)
Thanks to Bruno Daudin, CEA Grenoble

16. Self-organized growth of InN NWs

17. Growth details J. Segura et al, ICNS7 (Las Vegas), 2007.
InN nanocolumns growth:
Grown by plasma-assisted MBE.
p-Si (111) substrate.
Growth time of 300 minutes.
N2 rich conditions.
Sample
Ts (ºC)
In-BEP
(10-8 mbar)
N2 Flux
(sccm)
G053
400
3.0
2.0
G071
475
G047
500
G044
1.5
G041
Two sets of samples:
Set A: Different substrate temperature.
Set B: Different In-BEP and N2 flux conditions.
Ts: Substrate temperature.
In-BEP: Base equivalent pressure of In.
J. Segura et al, ICNS7 (Las Vegas), 2007.

18. Raman modes of the wurtzite structure
G=2A1+2B1+2E1+2E
447 (TO)
585.4 (LO)
476 (TO) 593 (LO)
InN 87
490.1 cm-1
Wurtzite : hexagonal structure with 4 atoms in the unit cell.
546 (TO)
732 (LO)
555 (TO) 741 (LO)
GaN
137
592 cm-1

19. Raman scattering results
Sample
E2h*
FWHM (E2h)
E1(LO)
FWHM (E1(LO))
G041
489,46
3,62
592,83
7,29
G071
489,24
3,45
592,53
7,79
G047
3,51
592,73
9,14
G044
488,92
4,45
591,42
7,55
G053
489,36
4,20
592,00
9,22
Very narrow E2h non polar mode peak, an indication of the high crystalline quality
Forbidden modes
Lower plasmon-LO coupled (PLP-) mode is observed
*X. Wang et al. Appl. Phys. Lett. 89, (2006).

20. Raman results
NCs homogeneous (G041) or with tapering effect (G071).
NCs with Baseball bate shape (G047) and coalescence (G053).
Forbidden modes can be observed in the Raman spectra because the laser light enters and scatters mainly from the lateral surface of the NCs.
Higher intensity of E1(LO) peak is observed in samples with morphologies which allow an easier access to the NCs lateral surface.
J. Segura et al, ICNS7 (Las Vegas), 2007; J. Segura et al, Phys. Rev. B 79, (2009).

21. Conclusions GaN QDs InN NWs
GaN QDs grown along the c axis emit in the green region of the spectrum due to the Stark effect
GaN QDs grown on non polar directions show quantum confinement and emit in the UV
InN NWs
NCs have a high crystalline quality and are strain-free
The appearance of forbidden modes has been correlated to the sample morphology
Raman scattering shows the existence of two emitting regions, a surface region giving rise to PLP modes and an inner region