Transcript Tayo Olukoya LBNL_GaTe_presentation_Fa12

Characterization of layered
gallium telluride (GaTe)
Omotayo O Olukoya (Chabot College)
PI : Oscar Dubon
Mentor : Jose Fonseca Vega
Lawrence Berkeley National lab
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Layered semiconductors
• Complex structure
• Manipulate band-gap.
Chalcogenide
• Recent discovery
0.8
1.6
2.4
3.2 nm
GaSe
adapted from D. V. Rybkovskiy et al., PRB (2011)
MoS2
GaTe (1.045 nm)
Mak, K.F., et al., Phys Rev Lett. 105, 136805 (2010).
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GaTe
• What do we know?
a. Monoclinic crystalline structure in bulk.
parameter constant: a = 17.44 Å, b = 10.456 Å,
Å,ϒ = 104.4o
c = 4.077
b. Goes from monoclinic to
hexagonal in thin films
c. Direct band gap of 1.69 eV at room temperature.
d. P - type
Hall effect
measurement
Experimental
Literature1
1
Carrier
Concentration
(cm-3)
3.74 x 1016
9 x 1015 – 8 x 1016
Mobility (cm2/V·s)
Resistivity
(ohm cm)
22
4.8 -21
7.6
7 - 40
Efeoğlu, H., et.al., Semicond. Sci. Technol. 19, (2004) 523-530
• What to look for?
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Method
 Substrate treatment
• 300 nm of thermally oxidized SiO2 on Si
was used.
• Ultra sonication

Isopropyl alcohol
 Acetone
• Oxygen plasma
• Standard RCA cleansing method
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Method cont.
 Mechanical exfoliation
 Scotch tape method was develop by Andre Geim
 Transfer
Optical microscopy
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Method cont.
Atomic Force microscopy (AFM)
• Tapping mode
AFM images
8 nm
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Method cont.
 Raman spectroscopy
o A 15mW Ar ion laser (514.5 nm) was
used.
 Photoluminescence
spectroscopy (PL)
o A 488 nm blue laser
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Raman result
• Raman spectra cont.
a. New peaks between 140 & 280 of Raman shift
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Raman’s result cont.
• Raman spectra
b. Horizontal shift
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PL result
• Correlation between laser intensity and counts
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PL result cont.
• Correlation between thickness and count
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Conclusion
 GaTe exhibits some anisotropic features.
 It will take further research to know what
properties are actually isolated from bulk.
Great chances of being able to cleave
down to a monolayer on SiO2 substrate.
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Next step
• Cleave down to a
monolayer
• Take more Raman
• Take low
temperature PL
• Devices and
application?
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Acknowledgment
• Prof Oscar Dubon (PI)
• Jose Fonseca Vega (mentor)
• Dubon’s Group
– Alex Luce (PL)
– Erick Ulin-Avila
• Dr. Sharnia Artis
• Shuk H Chan
• Center for Energy Efficient Electronics (E3S)
• National Science Foundation (NSF)
Q&A
?
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