2012 Transfer-to-Excellence Research Experiences for Undergraduates Program (TTE REU) 1

Characterization of layered gallium telluride (GaTe)

Omotayo O Olukoya (Chabot College)PI : Oscar Dubon

Mentor : Jose Fonseca VegaLawrence Berkeley National lab

2012 Transfer-to-Excellence Research Experiences for Undergraduates Program (TTE REU) 2

Layered semiconductors• Complex structure• Manipulate band-gap.

GaTe (1.045 nm)

• Recent discovery

0.8 1.6 2.4 3.2 nm

adapted from D. V. Rybkovskiy et al., PRB (2011)

Mak, K.F., et al., Phys Rev Lett. 105, 136805 (2010).

GaSe

MoS2

Chalcogenide

2012 Transfer-to-Excellence Research Experiences for Undergraduates Program (TTE REU) 3

GaTe

a. Monoclinic crystalline structure in bulk. parameter constant: a = 17.44 Å, b = 10.456 Å, c = 4.077

Å,ϒ = 104.4o

b. Goes from monoclinic to hexagonal in thin films

d. P - type

• What to look for?

c. Direct band gap of 1.69 eV at room temperature.

• What do we know?

2012 Transfer-to-Excellence Research Experiences for Undergraduates Program (TTE REU) 4

Method

• 300 nm of thermally oxidized SiO2 on Si

was used.

• Ultra sonication

Isopropyl alcohol

Acetone

• Oxygen plasma

• Standard RCA cleansing method

Substrate treatment

2012 Transfer-to-Excellence Research Experiences for Undergraduates Program (TTE REU) 5

Method cont. Scotch tape method was develop by Andre Geim

Optical microscopy

Mechanical exfoliation

Transfer

2012 Transfer-to-Excellence Research Experiences for Undergraduates Program (TTE REU) 6

Method cont.Atomic Force microscopy (AFM)

• Tapping mode

AFM images

8 nm

2012 Transfer-to-Excellence Research Experiences for Undergraduates Program (TTE REU) 7

Method cont.

Raman spectroscopyo A 15mW Ar ion laser (514.5 nm) was

used.

Photoluminescence spectroscopy (PL)o A 488 nm blue laser

2012 Transfer-to-Excellence Research Experiences for Undergraduates Program (TTE REU) 8

Raman result• Raman spectra cont. a. New peaks between 140 & 280 of Raman shift

2012 Transfer-to-Excellence Research Experiences for Undergraduates Program (TTE REU)

Raman’s result cont.

• Raman spectrab. Horizontal shift

2012 Transfer-to-Excellence Research Experiences for Undergraduates Program (TTE REU) 10

PL result• Correlation between laser intensity and counts

2012 Transfer-to-Excellence Research Experiences for Undergraduates Program (TTE REU) 11

PL result cont.• Correlation between thickness and count

2012 Transfer-to-Excellence Research Experiences for Undergraduates Program (TTE REU) 12

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.

2012 Transfer-to-Excellence Research Experiences for Undergraduates Program (TTE REU) 13

Next step

• Cleave down to a monolayer

• Take more Raman• Take low

temperature PL• Devices and

application?

2012 Transfer-to-Excellence Research Experiences for Undergraduates Program (TTE REU) 14

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 ?