Oxide Molecular-Beam Epitaxy

1. Oxide Molecular-Beam Epitaxy:
Oxide Molecular-Beam Epitaxy:
An Introduction with Examples
An Introduction with Examples
Darrell G. Schlom
Department of Materials Science and Engineering
Cornell University

2. Sandwich Maker
Sandwich Maker
http://www.engineering.cornell.edu/faculty/new-faculty/new-faculty-2008/schlom.cfm

3. Quantum
Cascade Laser
Yanbo Bai
http://www.yanbobai.com

4. TEM of MBE-Grown Superlattices
TEM of MBE-Grown Superlattices
AlAs / GaAs PbTiO3 / SrTiO3 BaTiO3 / SrTiO3
C.D. Theis J.H. Haeni
A.K. Gutakovskii et al., (1st Generation Schlom Group) (2nd Generation)
Phys. Stat. Sol. (a) 150 (1995) 127. HRTEM—Pan Group (Michigan)
D.G. Schlom et al., Mater. Sci. Eng. B 87 (2001) 282.

5. MBE ≈ Atomic Spray Painting
MBE ≈ Atomic Spray Painting

6. Key Enablers of MBE
Key Enablers of MBE
• “3-Temperaturaufdampfverfahren”
for Growth of III-V Semiconductor Films by
Vacuum Evaporation
K.G. Günther, “Aufdampfschichten aus
halbleitenden III-V Verbindungen,” Zeitschrift für
Naturforschung A 13 (1958) 1081-1089.
• Reliable UHV Sealing Technology
W.R. Wheeler and M. Carlson, “Ultra-High Vacuum
Flanges,” Transactions of the Eighth National
Vacuum Symposium, edited by L.E. Preuss
(Pergamon, New York, 1962), pp. 1309-1318.

7. Evolution of MBE
1st
University
MBE
Cornell,
1978
1st MBE Production
Al Cho at Bell Labs, 1972 MBE
Today
(courtesy of TRW)

8. MBE production tool performance data
HIGH YIELD
UNIFORMITIES / Wafer Thickness < ± 0.5 %
Composition < ± 0.5 %
Doping < ±1 %
REPRODUCIBILITY Source material: supply consistency
Stable process and monitoring: < 2%
HIGH THROUGHPUT
VERY HIGH UPTIME > 94%, run 6 to 9 months, 7 days/wk, 24/24
RUN CAPABILITY 13x2’’ or 5x3’’, 4x6’’ or 9x4’’, (4x8’’) 7x6’’
RUN SWITCHING less than 2 minutes (platen exchange)
8 May ‘03

9. Mobility Achieved with MBE
Mobility Achieved with MBE
A. Tsukazaki, S. Akasaka, K. Nakahara, Y. Ohno, H. Ohno,
D. Maryenko, A. Ohtomo, and M. Kawasaki L. Pfeiffer and K.W. West, Physics E 20 (2003) 57-64.
Nature Materials 9 (2010) 889-893.
D.G. Schlom and L.N. Pfeiffer, Nature Materials 9 (2010) 881-883.

10. Modulation Doping
R. Dingle, H.L. Störmer, A.C. Gossard, and W. Wiegmann, Applied Physics Letters 33 (1978) 665-667.
W.P. McCray, Nature Nanotechnology 2 (2007) 259-261.

11. Reflection High‐
Energy Electron
Diffraction (RHEED)
Oscillations
B. Bölger and P. K. Larsen, Review of Scientific B.A. Joyce, P.J. Dobson, J.H. Neave, K.
Instruments 57 (1986) 1363-1367. Woodbridge, J. Zhang, P.K. Larsen, and B Bölger,
Surface Science 168 (1986) 423-438.

12. J. Heber, Nature 459 (2009) 28-30.

13. XRD of (BaTiO33))nn // (SrTiO33))m Superlattices
XRD of (BaTiO (SrTiO m Superlattices
m=4 m = 13
A. Soukiassian, W. Tian, V. Vaithyanathan, J.H. Haeni, L.Q. Chen, X.X. Xi, D.G. Schlom, D.A. Tenne, H.P. Sun, X.Q. Pan,
K.J. Choi, C.B. Eom, Y.L. Li, Q.X. Jia, C. Constantin, R.M. Feenstra, M. Bernhagen, P. Reiche, and R. Uecker,
Journal of Materials Research 23 (2008) 1417-1432.

14. Intensity (arbitrary units)
10
10
10
10
2
3
4
5
0
003
004
005
006
007
008
009
0010
0011
0012
0013
0014
0015
10
0016
0017
0018
0019
0020
0021
0022
0023
c = 121.4 ± 1.3 Å
0024
0025
0026
0027
0028
20
0029
-
2
10
ω
10
0400
-100
-200
-300
(arc
seconds)
S
0030 0031
XRD of [(BaTiO
*
0032
0033
0034
0035
0036
0037
0038
0039
0040
0041
0042
30
0043
0044
0045
0046
2θ (degrees)
0047
0048
0049
0050
0051
0052
0053
0054
0055
40
0056
0057
0058
0059
0060
0061
0062
*
0063
0064
0065
0066
0067
0068
50
XRD of [(BaTiO33))11 // (SrTiO33))30]]20
(SrTiO 30 20
Superlattice grown on (001) SrTiO
Superlattice grown on (001) SrTiO33

15. Creating New Materials
Creating New Materials
(SrTiO3)30
SrTiO3
(BaTiO3)1
(SrTiO3)30 BaTiO3
High Angle Annular Dark Field
STEM Collaboration with David Muller
(Cornell, Applied Physics)

16. Creating New Materials
Creating New Materials
(SrTiO3)30
SrTiO3
(BaTiO3)1
(SrTiO3)30 BaTiO3
BaTiO3 / SrTiO3
STEM-EELS Collaboration with David Muller
(Cornell, Applied Physics)

17. NanoEngineering
NanoEngineering
of Oxides
of Oxides
e.g., Srn+1TinnO3n+1
e.g., Srn+1Ti O3n+1
Homologous
Homologous
Series
Series
J.H. Haeni, C.D. Theis, D.G. Schlom, W. Tian, X.Q. Pan, H. Chang, I. Takeuchi, and X.-D. Xiang,
Applied Physics Letters 78 (2001) 3292-3294.

18. Intensity (arb. units)
004
006
008
10
0010
0012
0014
0016
0018
20
*
0024
0026
0028
30
0030
0032
0034
0036
40
0038
2θ (degrees)
0040
0044
*
50 0046
0048
0050
0052
60
0054
0056
150 nm Sr11Ti10O31 // (001) SrTiO33 ((n = 10)
150 nm Sr11Ti10O31 (001) SrTiO n = 10)

19. Outline

20. Maximum O2 Pressure for MBE
Maximum O2 Pressure for MBE
106
Mean Free Path (cm) Li for Metal Flux of
105 1×1014 atoms/(cm2·s)
104
Ba
103
102
MBE Regime
101
100
π PO2 ⎛ di + dO2 ⎞ 5 ⎛ TO2 ⎞ ⎛ mi ⎞
2
-1
10 1
= ( Fi di )
π 2 2mi
+ ⎜ ⎟ 1 + ⎜ ⎟⎜ ⎟
Li 3kB Ti kB TO2 ⎝ 2 ⎠ 3 ⎝ Ti ⎠ ⎜ mO2 ⎟
⎝ ⎠
10-2
10-9 10-8 10-7 10-6 10-5 10-4 10-3 10-2 10-1
Oxygen Pressure (Torr)
D.G. Schlom and J.S. Harris, Jr., “MBE Growth of High Tc Superconductors,” in:
Molecular Beam Epitaxy: Applications to Key Materials, edited by R.F.C. Farrow (Noyes, Park Ridge, 1995), pp. 505-622.

21. O22 Needed to Oxidize Constituents
O Needed to Oxidize Constituents
900 800 700 600 500 °C
Oxygen Pressure (Torr)
2 Bi + O
10-10
2 ⌦ 2 Bi O
2 3
2 Pb + O
10-20 4 Nb 2 ⌦ 2 PbO
+5O
2 ⌦2
-30 Ti + Nb O
10 O2 ⌦ 2 5
TiO
2
10-40 2 Sr 4 Ta
+5O
+O 2 ⌦ 2
2 ⌦ Ta O
10-50 2 Ba
+O
2 Sr
O
2 5
2 ⌦
10-60 2 Ba
O
-70
10
0.90 1.00 1.10 1.20 1.30 1.40
1000/T (1/K)

22. O2 Needed to Oxidize Cuprates
O2 Needed to Oxidize Cuprates
-1 900 800 700 600 500 400 °C
10
Oxygen Pressure (Torr)
CuO 10-1
Mean Free Path (cm)
10-2 Bi2Sr2Ca2Cu3O10
100
10-3 Bi2Sr2CaCu2O8
YBa2Cu3O7-δ 101
10-4 MBE Regime
102
10-5
103
10-6
104
10-7
105
10-8
106
10-9
0.8 1.0 1.2 1.4 1.6
1000/T (1/K)
D.G. Schlom and J.S. Harris, Jr., “MBE Growth of High Tc Superconductors,” in:
Molecular Beam Epitaxy: Applications to Key Materials, edited by R.F.C. Farrow (Noyes, Park Ridge, 1995), pp. 505-622.

23. Pros and Cons of Ozone
Pros and Cons of Ozone
• Pros
– Excellent Oxidant (about 1000x more powerful than O2)
– 80% Ozone (+20% O2) Delivery Possible to the Substrate
– No Energetic Species (thermal ozone beam)
– Inexpensive (if you make it yourself)
• Cons
– Safety (Ozone still issues)
– Safety (Pump issues)
– Need Ozone-Compatible UHV Leak Valve
– Need to Passivate Ozone System

24. Outline

25. Thermodynamic Considerations

26. TEM of MBE-Grown Superlattices
TEM of MBE-Grown Superlattices
AlAs / GaAs PbTiO3 / SrTiO3 BaTiO3 / SrTiO3
C.D. Theis J.H. Haeni
A.K. Gutakovskii et al., (1st Generation Schlom Group) (2nd Generation)
Phys. Stat. Sol. (a) 150 (1995) 127. HRTEM—Pan Group (Michigan)
D.G. Schlom et al., Mater. Sci. Eng. B 87 (2001) 282.

27. Increased Interface
Roughness and
Clustering at
Non‐Optimal
Growth Conditions
W. Barvosa-Carter, M.E. Twigg, M.J. Yang, and L.J. Whitman, Physical Review B 63 (2001) 245311.

28. Surface Energy Considerations
K.-N. Tu, J.W. Mayer, and L.C. Feldman,
Electronic Thin Film Science for Electrical Engineers and Materials Scientists (Macmillan, 1992).

29. Surface vs. Bulk Diffusion
Assuming growth rate of
0.1 monolayer/sec
Tmin for smooth epitaxial films
(growth by step propagation)
Tmin for epitaxy
Tmax Optimal Growth Temperatures
T sub
0 .55 < < 0 .7 for semiconductors
T melt
T sub
0 .35 < < 0 .4 for metals
T melt
T sub
0 .1 < < 0 .4 for simple ceramics
T melt
M.H. Yang and C.P. Flynn,
Physical Review Letters 62
(1989) 2476-2479.

30. Universal Diffusion Behavior of Metals
−Q
D=D e 0
R Tm
C. Peter Flynn, Point Defects and Diffusion (Oxford, 1972) pp. 783-785.

31. Determining Surface Diffusion from
RHEED Oscillations
J.H. Neave, P.J. Dobson, B.A. Joyce, and J. Zhang,
Applied Physics Letters 47 (1985) 100-102.

32. Surface vs. Bulk Diffusion
Assuming growth rate of
0.1 monolayer/sec
Tmin for smooth epitaxial films
(growth by step propagation)
Tmin for epitaxy
Tmax Optimal Growth Temperatures
T sub
0 .55 < < 0 .7 for semiconductors
T melt
T sub
0 .35 < < 0 .4 for metals
T melt
T sub
0 .1 < < 0 .4 for simple ceramics
T melt
M.H. Yang and C.P. Flynn,
Physical Review Letters 62
(1989) 2476-2479.

33. Adsorption‐Controlled Growth of GaAs
Temperature (°C)
104 700 650 600 550 500
4 As(s)⇔ As4 (g)
Gas Pressure (Torr)
10-1
2 GaAs(s)⇔ 2 Ga(l) + As2 (g)
10-6
10-11
1.05 1.10 1.15 1.20 1.25
1000/T (1/K)

34. Adsorption‐Controlled Growth of EuO
Eu Flux = 1.1×1014 Eu atoms/(cm2 s)
EuO film thickness (from RBS) after 30 min
R.W. Ulbricht, A. Schmehl, T. Heeg, J. Schubert, and D.G. Schlom,
Applied Physics Letters 93 (2008) 102105.

35. Adsorption-Controlled MBE
Adsorption-Controlled MBE
Atomic Flux (Φ) (atoms/cm2 sec)
1024
22
4 As(s) ⇔ As
10 4 (g)
1020
1018
1016 2 GaAs(s) ⇔ 2 Ga(l) + As2 (g)
1014 ΦBi O
12 x y (g)
10
ΦBi O Bi2O3 (s)
1010 x y (g)
10 8 Bi4Ti3O12 (s) + TiO2 (s)
700 650 600 550 500
Temperature (°C)
D.G. Schlom, J.H. Haeni, J. Lettieri, C.D. Theis, W. Tian, J.C. Jiang, and X.Q. Pan, Mat. Sci. Eng. B, 87 (2001) 282-291.

36. Adsorption-Controlled MBE
Adsorption-Controlled MBE
Bi Flux (always open)
Relative Flux
O2/O3 (always open)
Fe Flux (monolayer doses)
Time

37. Adsorption-Controlled MBE
Adsorption-Controlled MBE
T (°C)
10-3 500 475 450 425 400
Φ Bi O
Φ x y (g)
O2 Pressure (Torr)
BixOy (g) Bi2O2.5 (s) + BiFeO3 (s)
10-5 BiFeO3 (s)
10-7
Φ
BixOy (g)
BiFeO3 (s) + γ-Fe2O3
10-9 (s)
1.30 1.35 1.40 1.45 1.50
1000/T (1/K)
J.F. Ihlefeld, N.J. Podraza, Z.K. Liu, R.C. Rai, X. Xu, T. Heeg, Y.B. Chen, J. Li, R.W. Collins, J.L. Musfeldt,
X.Q. Pan, J. Schubert, R. Ramesh, and D.G. Schlom, Applied Physics Letters 92, 142908 (2008).

38. Epitaxial BiFeO33 // (001) SrTiO33
Epitaxial BiFeO (001) SrTiO
Adsorption-Controlled Growth
Adsorption-Controlled Growth
BiFeO3 + γ-Fe2O3 BiFeO3 + Bi2O2.5
Fe Closed
Tsub ~ 500°C Tsub ~ 400°C
ΦBi Fe Open
= 7.0
ΦFe
Tsub ~ 450°C
J.F. Ihlefeld, N.J. Podraza, Z.K. Liu, R.C. Rai, X. Xu, T. Heeg, Y.B. Chen, J. Li, R.W. Collins, J.L. Musfeldt, X.Q. Pan, J. Schubert,
R. Ramesh, and D.G. Schlom“Optical Band Gap of BiFeO3 Grown by Molecular-Beam Epitaxy” Applied Physics Letters 92, 142908 (2008)

40. Flux-Controlled MBE Growth of
Flux-Controlled MBE Growth of
(BaTiO33))55 // (SrTiO33))55 Superlattice
(BaTiO (SrTiO Superlattice

41. Outline

42. How we do it
How we do it
• Use Quartz Crystal Microbalance to Get Fluxes
Close (~5% accuracy)
• Use Shuttered RHEED Oscillations
(analogous to MEE of GaAs)
• Yields Sr:Ti Relative Incorporation Ratio
(~1% accuracy)
• Yields Absolute Monolayer Dose for SrO and TiO2
(~1% accuracy)
• Works for Other Perovskites too (BaTiO3, SrRuO3)
J.H. Haeni, C.D. Theis, and D.G. Schlom, Journal of Electroceramics 4 (2000) 385-391.

43. Reflection High‐
Energy Electron
Diffraction (RHEED)
Oscillations
B. Bölger and P. K. Larsen, Review of Scientific B.A. Joyce, P.J. Dobson, J.H. Neave, K.
Instruments 57 (1986) 1363-1367. Woodbridge, J. Zhang, P.K. Larsen, and B Bölger,
Surface Science 168 (1986) 423-438.

44. Conventional RHEED Oscillations
Molecular Beam Epitaxy: Applications to Key Materials,
edited by R.F.C. Farrow (Noyes, Park Ridge, 1995), p. 694.

45. Shuttered RHEED to Get Sr:Ti = 1:1
3 % Ti Rich 3 % Ti Poor
Stoichiometric SrTiO3 [011] Azimuth
Oscillations of the central diffracted rod as the Sr and Ti
are deposited in a sequential manner
J.H. Haeni, C.D. Theis, and D.G. Schlom, Journal of Electroceramics 4 (2000) 385-391.

46. Shuttered RHEED Oscillations
Shuttered RHEED Oscillations

47. Shuttered RHEED Oscillations
Shuttered RHEED Oscillations
A-Site Rich B-Site Rich

49. Beat Frequency for Sr:Ti = 1:1 Absolute
J.H. Haeni, C.D. Theis, and D.G. Schlom, Journal of Electroceramics 4 (2000) 385-391.

50. Outline

51. Oxide MBE at Brookhaven Nat. Lab.
Oxide MBE at Brookhaven Nat. Lab.

52. Oxide MBE + ARPES
Oxide MBE + ARPES
Collaboration with Kyle Shen (Cornell, Physics)

53. Reactive Molecular-Beam Epitaxy
Reactive Molecular-Beam Epitaxy

58. R.E. Honig and D.A. Kramer, RCA Review 30 (1969) 285-305.

59. R.E. Honig and D.A. Kramer, RCA Review 30 (1969) 285-305.

60. V
Pb
R.E. Honig and D.A. Kramer, RCA Review 30 (1969) 285-305.

61. Binary Alloy Phase Diagrams,
edited by T.B. Massalski (ASM International, 1990).

62. Binary Alloy Phase Diagrams,
edited by T.B. Massalski (ASM International, 1990).

63. Binary Alloy Phase Diagrams,
edited by T.B. Massalski (ASM International, 1990).

64. V
R.E. Honig and D.A. Kramer, RCA Review 30 (1969) 285-305.

65. Kurt J. Lesker, Co. Catalog

66. Binary Alloy Phase Diagrams,
edited by T.B. Massalski (ASM International, 1990).

67. Outline

68. Substrates are Key
Substrates are Key

69. Commercial Perovskite Substrates
Commercial Perovskite Substrates
D.G. Schlom, L.Q. Chen,
X.Q. Pan, A. Schmehl,
and M.A. Zurbuchen,
Journal of the American
Ceramic Society 91
(2008) 2429-2454.

70. MBE vs. Single Crystals (Rocking Curves)

72. Surface Termination Recipes
Surface Termination Recipes
• (001) SrTiO3
G. Koster, B. L. Kropman, G. J. H. M. Rijnders, D. H. A. Blank,
H. Rogalla, “Quasi-Ideal Strontium Titanate Crystal Surfaces through
Formation of Strontium Hydroxide,” Appl. Phys. Lett. 73 (1998)
2920-2922.
• (110) REScO3
J.E. Kleibeuker, G. Koster, W. Siemons, D. Dubbink, B. Kuiper,
J.L. Blok, C-H. Yang, J. Ravichandran, R. Ramesh, J.E. ten Elshof,
D.H.A. Blank, and G. Rijnders, “Atomically Defined Rare-Earth
Scandate Crystal Surfaces,” Advanced Materials 20 (2010) 3490-
3496.
• (001) LSAT
J.H. Ngai, T.C. Schwendemann, A.E. Walker, Y. Segal, F.J. Walker,
E.I. Altman, and C.H. Ahn, “Achieving A-Site Termination on
La0.18Sr0.82Al0.59Ta0.41O3 Substrates,” Advanced Materials 22 (2010)
2945-2948.

73. Terminated vs. Unterminated SrTiO3
RHEED Intensity (arb. units)
(BaTiO ) (SrTiO ) (BaTiO3)4 (SrTiO ) (BaTiO ) (SrTiO )
3 4 3 2 3 2 3 4 3 2
Ti shutter open
[110] azimuth
Not
Terminated
Sr shutter open
Ba shutter open
0 200 400 600 800
Time (s)
RHEED Intensity (arb. units) Ti shutter open
[100] azimuth
Terminated
Ba shutter open Sr shutter open
0 100 200 300 400 500 600 700
Time (s)

74. MBE Summary
MBE Summary
Advantages Disadvantages
• Extreme Flexibility • Extreme Flexibility
(uncontrolled flexibility =
• Independent Growth chaos!)
Parameters
• High Cost
• Compatible with wide range
of in situ Diagnostics • Long Set-up Time
• Clean • MBE (the other meanings…)
• Gentle
• Precise Layering Control at
the Atomic Level