Optical properties of iii-n nanostructures

1. 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 CertamenInternacional 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 itsUniversity Valencia, 138 bce 810,000 p;1,500,000 mr Wehave 45,000 students TheUniversitywasfounded in 1499

4. Outline • Interest in nitride semiconductors: applications • Generalitieson III-N semiconductors • GaN/AlNself-assembled quantum dots • Growth of GaN/AlN/SiCself-assembledQDs • Opticalproperties of polar and non polar QDs • Q1D semiconductor nanostructures • InN nanowires • Growth of InN nanowires • Opticalproperties of InN nanowires • Conclusions

5. Opticalstoragedevices Sony launchesits Blue-rayrecorder (Sept 20th, 2006) 54 Gbcapacity 400 nm laser (NichiaCorp) Prof. Nakamura (UCSB) fabricated a 443.9 nm laser basedon NP InGaN/GaN

6. White LEDs 1st prize street (ecological) illumination Fallas 2009 Kittilä (Finland) , 2.2.2009

7. Nitridesemiconductors

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

9. 1010disl/cm2 Structuralparameters and PSP But, itisgrownon Al2O3, SiCor Si(111) Thereis, additionally, PPZ F. Bernardini, V. Fiorentini, D. Vanderbilt, PRB 56, R10024 (1997).

10. Ga [ [ ] ] 0001 0001 AlN AlN GaN GaN dot dot [2 [2 - - 1 1 - - 10] 10] Ga+ N AlN AlN 2nm 2nm AlN Growth of GaN/AlN QDs ModifiedStranski-Krastanowmode 6H-SiC Elasticrelaxation 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/AlNQWs F=10 MV/cm Thebuilt in electricfieldmanifests in theopticalproperties of GaN/AlNheterostructuresthroughtheStarkeffect Isthere a wayto reduce dislocations and Starkeffect? (a): J. M. Llorens, PhD (2006), Univ. Valencia; (b) Salviati et al., J. Phys. Cond. Matt. 16, S115 (2004); (c) Miyamura et al., APL 80 3937 (2002); (d) Kako et al., APL 83, 984 (2003); (e) Widmann et al., APL 83, 7619 (1998).

12. 5 nm [1-100] [1120] [0001] Plano a [0001] Non polar QDs a- and m-planecontainthesameamount of Ga and N per layer HRTEM AFM S. Founta et al, APL 86, 171901 (2005) N. Garro et al., APL 87, 011101 (2005)

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

14. Growinginterest in SNWs Publishedpaperson semiconductor NWs (Web of Sciences) Comparison of thenumber of citationsonQDs and NWs • Quasi-one dimensional symmetry • Largesurface/volume ratio • New possibleheterostructures • Highqualitymaterials (strain free) • Highqualityheterointerfaces (larger LM)

15. From QWs to NWs GaN grown on AlN Fixed N flux Ga bilayer conditions GaN AlN N-rich conditions • Ingredients: • latticemismatch • (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 • InN nanocolumns growth: • Grown by plasma-assisted MBE. • p-Si (111) substrate. • Growth time of 300 minutes. • N2 rich conditions. 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. Ramanscatteringresults 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, 171907 (2006).

20. Ramanresults 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, 115305 (2009).

21. Conclusions • GaN QDs • 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