Roland Weingärtner

1. Bandgap Engineering of the Amorphous Wide Band-GapSemiconductor (SiC)1-x(AlN)xDoped with Rare Earths and itsOptical Emission Properties Roland Weingärtner San Miguel, 14th of April 2011 Departamento de Ciencias – Sección Física – Grupo Ciencias de los Materiales Pontificia Universidad Católica del Perú (PUCP)

2. Outline I Motivation and Introduction • Wide band-gap semiconductors • Band-gap engineering • Rare earth doping and optical emission II First Results of a-(SiC)x(AlN)1-x • Thin film growth method and structural characterisation • Band-gap engineering of a-(SiC)x(AlN)1-x III Cathodoluminescense measurements • Spectral emission of rare earth doped a-(SiC)x(AlN)1-x • Thermal activation of rare earth emission IV Summary and Acknowledgements

3. Why wide band-gap semiconductors ? Principal idea: Combine the advantages of an insulator and a semiconductor Advantage of a semiconductor: Active electronic devices like diodes, transistors, etc Advantage of an insulator: Due to the wide band-gap the samples are transparent Historic development: GaN based LED

4. Band-gap engineering • The band-gap has influence on: • Emission wavelength of an optical device • efficiency of the light emission • energy level of the dopants • etc. AxB1-x Variation of the band-gap by changing the composition Choose an optimal composition for a specific application

5. Small overview of semiconductors Wide band-gap

6. Why rare earth doping in semiconductors ? • Optical emission properties of rare earths: • emission wavelength does not depend on the host material • Color is typical for a specific rare earth ion • Intensity of rare earth emission depends on the material: • band-gap quenching • temperature quenching • concentration quenching

7. Colors in rare earth doped GaN M. Garter et al. Appl. Phys. Lett. 74 (1999) p.182

8. Excitation mechanism Cathodoluminescense of RE3+ in a-AlN:RE Intrashell-transitions of f-shells RE3+ Ion 1 and 2: excitation paths a and b: recombination paths

9. Temperature quenching of Er3+ doped semiconductors • In0,16Ga0,38As0,84P0,16 • Si • InP • GaAs • Al0,17Ga0,83As • ZnTe • CdS Increase of band-gap From Favennec: Electronics Letters 25 (1989) 718

10. Temperature quenching for Er3+ emission From Zanatta: Appl. Phys. Lett. 82 1395 (2003)

11. Temperature quenching in AlN:RE Phenomenological description: From Lozykowski and Jadwisienczak: Phys. Stat. Sol. B 244 (2007) 2109

12. Outline I Motivation and Introduction • Wide band-gap semiconductors • Band-gap engineering • Rare earth doping and optical emission II First Results of a-(SiC)x(AlN)1-x • Thin film growth method and structural characterisation • Band-gap engineering of a-(SiC)x(AlN)1-x III Cathodoluminescense measurements • Spectral emission of rare earth doped a-(SiC)x(AlN)1-x • Thermal activation of rare earth emission IV Summary and Acknowledgements

13. Why a-(SiC)x(AlN)1-x? • Wide bandgap semiconductors: • Increase of rare earth emission • Lower temperature quenching • Transparent • Semiconductor devices • Rare earth doping: • Well defined emission color • Covering of the whole color range a-(SiC)x(AlN)1-x:RE • Amorphous films: • Inexpensive • Simple production • Higher incorporation of rare earths • Pseudobinary compound: • Band-gap engineering (3eV to 6eV) • one composition parameter • Sputtering from SiC and AlN target

14. Los principios de dc-sputtering sustrato + + + + + + + + - target 10-2 mbar 1000 V ánodo + ion Ar Átomo Ar electrón Problemas: Plasma frío: • Inestabilidad del plasma • Sólo targets metálicos • Baja eficiencia

15. Los principios de magnetrón-sputtering Aumento de densidad de los iones Más rapidez del crecimiento

16. El magnetrón portatarget blindaje Anillo de plasma target magnetrón armado N S S S N N

17. Schematics of the sputtering system Mass spectrometer Control of mass spectrometer H2O shutter Mass flow controler substrate targets Pressure sensor Rf- generator Rf-generator flexible magnetrons Turbo-molecular pump H2O match control Mechanicalpump N2 PC control Ar

18. The rf magnetron sputter system at the PUCP • Vacuum system: • residual gas analysis • Gas processing: • flow control of N2, H2and Ar: 0…100 sccm, 5N...6N • working pressure: Sputter targets: • trial magnetron sputtering, 2´´ • 3 Rf generators, P<300W • felxible target geometry !! Substrates: • Substrate area up to 128 cm2 • variable target substrate distance • water cooled substrate holder

19. A typical film of a-SiC on glas Target material: Silicon Carbide (SiC) Substrate material: fused glas Rf power: 100 W Process gas: Argon, 5N Gas flow: 80 sccm Argon pressure: 810-3 mbar 3´ a-SiC 3´

20. Característica de emisión de un magnetrón I 80403 80402 80401 80331 80327

21. Característica de emisión de un magnetrón II emisión en uu. aa. Contorno de emisión 1cm plasma target N S S S blindaje N N imanes

22. A typical thin film of a-(SiC)x(AlN)1-x EDX results host substrate • highly pure films (i.e. Na content < 8 ppm wt.) • no signature of impurities in the film

23. Structure of a/nc-AlN and a-SiC anealed at 900°C Transmission electron microscopy (TEM): diffraction a/nc-AlN a-SiC Substrate (Si) High resolution transmission electron microscopy (HRTEM): a/nc-AlN There are nanocrystals embedded in an amorphous matrix

24. Optical absorption measurements Determination of the band-gap i.e. a-(SiC)0.25(AlN)0.75:

25. Band-gap engineering of a-(SiC)x(AlN)1-x [1] Nurmagomedov et al.: Sov. Phys. Semicond. 23 100 (1989) [2] Gurumurugan et al.: Appl. Phys. Lett. 74 3008 (1999) [3] Zanatta et al.: J. Phys. D: Appl. Phys. 42 (2009) 025109 Fitting to Vegard´s law: Bowing parameters: ba2=(1.98±0.94) eV , bTauc=(1.96±0.48) eV

26. Outline I Motivation and Introduction • Wide band-gap semiconductors • Band-gap engineering • Rare earth doping and optical emission II First Results of a-(SiC)x(AlN)1-x • Thin film growth method and structural characterisation • Band-gap engineering of a-(SiC)x(AlN)1-x III Cathodoluminescense measurements • Spectral emission of rare earth doped a-(SiC)x(AlN)1-x • Thermal activation of rare earth emission IV Summary and Acknoledgements

27. Emission of rare earth ions in a/nc-AlN and a-SiC Cathodoluminescense of RE3+ in a-AlN:RE Cathodoluminescense of RE3+ in a-SiC:RE

28. Thermal activation of a-/nc-AlN • exponential growth with the anealing temperature • there is a saturation of the RE emission at anealing tempertures of 900°C

29. Thermal activation of a-SiC • exponential growth with anealing temperature • there is no saturation up to 1000°C • there is an optimal anealing temperature for the Tb3+ emission in a-SiC

30. Thermal activation of a-(SiC)x(AlN)1-x

31. Thermal activation of a-(SiC)0.83(AlN)0.17:Tb3+

32. Summary Wide-bandgap semiconductors • Rare earth doping • bandgap engineering First results on a-(SiC)x(AlN)1-x thin films • HRTEM investigations • bandgap engineering of a-(SiC)x(AlN)1-x Cathodoluminescense • optical emission of a-(SiC)x(AlN)1-x • thermal activation of rare earth emission • Conferences/Publications: • IMRC 2009 in Cancun, Mexico (invited talk) • ICSCRM´2009 in Nuremberg, Germany • Five publications in International Journals

33. Acknowledgements Materials Department, University of Erlangen, Germany • Prof. Dr. Winnacker • Prof. Dr. H. P. Strunk • Catholic University of Lima, Peru (PUCP) • Prof. F. De Zela • Andrés Guerra, Gonzalo Galvez, Oliver Erlenbach (PhD) • Liz Montañez, Katia Zegarra, (Licenciatura) • This research work is supported by the • Pontificia Universidad Católica del Peru (PUCP) • Deutsche Forschungsgemeinschaft (DFG) and the • German Service of Academic Interchange (DAAD)

34. Wide bandgap semiconductors From Steckl MRS Bull. 24, p. 33 (1999)