Semiconductor Nanostructures

Transcription

1 I H. von Känel Laboratorium für Festkörperphysik ETHZ

2 Moore s Law Doubling of transistor density in less than every 2 years

3 International Roadmap for Semiconductors

4 Evolution of LED performance Haitz law for red and blue LEDs M.R. Krames et al., J. Display Technol. 3,, 160 (2007)

5 Quantum efficiencies of HBLEDs J.M. Phillips et al. Laser & Photon Review 1, No. 4, 2007

6 Periodic table of elements

7 Diamond structure t

8 Zinc-blende structure t

9 Comparison of wurtzite and zinc- blende structures

10 Tetrahedrally bonded semiconductors (diamond, zinc blende)

11 Variation of bandgap with lattice parameter UV-green group III nitrides Yellow-red zinc blende arsenides - phosphides M.R. Krames et al., J. Display Technol. 3,, 160 (2007)

12 Consequences of strain Strain affects electronic structure, optical and transport t properties Strain affects crystal quality through defect formation Strain affects growth modes Strain affects the stability of phases

13 Epitaxial growth modes Frank-van der Merwe Volmer-Weber Stranski-Krastanow

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16 Structural data of group III nitrides Room temperature data for Lattice parameters Thermal expansion

17 Al 2 O 3 (0001) substrates Notice rotation of overlayer by 30 degrees! Misfit for GaN f = %

18 Si(111) substrates Misfit for GaN f = 16.9 %

19 Strain relieving mechanisms Plastic relaxation: Formation of misfit dislocations Elastic relaxation: Surface corrugation, island formation Formation of epitaxially stabilized phases

20 Strain relaxation by dislocations a) Coherent interface, compressively strained film b) Incoherent interface, relaxed film

21 Critical thickness for plastic relaxation a) Pure edge dislocations with Burgers vector b = 2.2 Å b) dislocations with b = 3.8 Å

22 Geometry of 60-degree dislocations (111) (001) TD - b=a/2[011] MD m n p [110] - [110] A.E. Blakeslee, MRS Symp. Proc. 148,, 217 (1989)

23 Propagation of dislocation loops in {111} planes

24 Dislocation control by patterning P. Zaumseil et al. J. Appl. Phys. 109, (2011) 60-degree dislocations A.E. Blakeslee, MRS Symp. Proc. 148,, 217 (1989)

25 Aspect ratio trapping (ART)

26 Lateral epitaxial overgrowth (LEO) Marachand et al. Appl. Phys. Lett. 73,, 747 (1998) 1. Nucleation in mask openings 2. Lateral overgrowth 3. Coalescence

27 Elastic strain relaxation by island formation

28 Normalized free energy for island formation F/F c = av 3/2 bv

29 STM monitoring of Ge island formation on Si(001) polycrystalline W tip V bias sample x,y drive piezo tube I t feedback z

30 Shape evolution sequence A. Rastelli et al., Phys. Rev. Lett ,, (2001) Prepyramid Pyramid T-Pyramid Super Dome Super-Dome T-Dome Dome nm nm3

31 GaN quantum dots on AlN HRTEM STEM T. Xu et al., J. Appl. Phys. 102,, (2007) Compressive misfit 2.5 % Truncated pyramidal shape Wetting layer visible ibl in STEM K. Hoshino et al., phys. Stat. Sol. (b) 240,, 322 (2003)

32 PbSe quantum dots on PbTe(111) G. Springholz et al., Science 282,, 734 (1998)

33 fcc ordering of dot SL G. Springholz et al. Science 282,, 734 (1998)

34 GaN columns on AlN/Si(111) Potential for columnar LEDs with much higher light extraction ti efficiency i

35 Epitaxial stabilization of phases

36 Cubic GaN/GaAs(001) A. Trampert and K. Ploog, Cryst. Res. Technol. 35, 793 (2000) Misfit 20%! Coincidence id lattice 5 a c-gan = 4 a GaAs GaAs

37 Mixing free energy of In x Ga 1-x N alloys Composition x A. Tabata et al., Appl. Phys. Lett. 80,, 769 (2002)

38 Alloy stabilization by biaxial strain A. Tabata et al., Appl. Phys. Lett. 80,, 769 (2002) a) Unstrained c-ingan alloys on c-gan(001) buffer b) Complete suppression of spinodal decomposition for T = T s

39 Thermal mismatch: Wafer bending and cracks 30 µm Ge/Si(001)

40 Growth on patterned Si substrates Micromachined Si pillars Ge coverage: 8 µm CV C.V. Falub betal al., Science 335,, 1330 (2012)

41 Self-limiting limiting lateral growth C.V. Falub et al., Science 335,, 1330 (2012)

42 Elastic relaxation of thermal strain C.V. Falub et al., Science 335,, 1330 (2012)

43 Characterization of epitaxial nanostructures Structural: Reflection high energy electron diffraction (RHEED) Optical reflection spectroscopy X-ray diffraction Transmission electron microscopy Secondary ion mass spectrometry (SIMS) Rutherford backscattering spectrometry (RBS) Optical: Reflection & transmission Photoluminescence Raman scattering Electrical: Conductivity & Hall effect

44 Molecular beam epitaxy

45 RHEED pattern from a rectangular 2-D lattice

46 Typical RHEED pattern (0 th Laue zone)

47 RHEED pattern of Si(111) Incident electron beam along <11-2> azimuth

48 Rough GaN layer on AlN buffer Diffraction spots due to transmission through islands

49 RHEED oscillations (schematic)

50 Coplanar high-angle x-ray diffraction

51 Coplanar high-angle x-ray diffraction

52 HRXRD analysis: 30 µm Ge towers vs. continuous film C.V. Falub et al., Science 335,, 1330 (2012)

53 HRXRD analysis of 30 µm Ge towers C.V. Falub et al., Science 335,, 1330 (2012)

54 Strain state of c-gan/ingan/gan(001) / (a) d InGaN = 30 nm Tabata et al. Appl. Phys. Lett. 80,, 769 (2002) (b) d InGaN = 3 nm

55 Near band edge PL of alloys S. Chichibu, nature materials 5, 810 (2006)

56 Periodic table of elements

57 GaN PL intensity vs. TDD Theory: J.H. You, J. Appl. Phys. 101,, (2007)

58 Al Al 0.09 Ga Ga 0.91 N/GaN heterostructure Sheet electron density Mobility cm 2 /Vs at 4 K cm -2 at 4 K 12 cm C.R. Elsass et al., Jap. J. Appl. Phys. 39, L1023 (2000)

59 Mobility limiting scattering mechanisms D. Jena et al., Am. Phys. Soc. March Meeting, Seattle, Washington, 2001

60 Elementary processes in epitaxy

61 III-V VMBEatLNESS L-NESS in Como

62 Generic CVD system

63 Epitaxial SiGe growth by CVD

64 Temperature dependence of CVD growth rates

65 CVD growth rate for Si homoepitaxy E.C. Everstyn, Philips Research Rept. 19,, 45 (1974)

66 Group III nitride MOCVD Aixtron planetary reactor Note numerous gas phase reactions M. Dauelsberg, ICMOVPE XIII, May , Miyazaki, Japan

67 Deposition of SiGe by LEPECVD 200 mm LEPECVD system Principle of low-energy plasma-enhanced CVD: High-current low-voltage arc discharge SiH 4 and GeH 4 are transformed into highly reactive radicals Ar Ar Ge Ar Si H H Ar Si Si H + + H H H Ar Ge Ar Ge Ar Ar Si Si H H Ar Ar H Ge H Si Ge H + H H Very high growth rates (0.5 µm/min) possible at low substrate temperatures

68 Hydride vapor phase epitaxy Typical substrate temperatures o C Growth rates of several 100 µm/h