Semiconducting Semiconducting -FeSi-FeSi22

Presented by

Srujana Aramalla

SilicidesSilicides

• Metallic Silicides

e.g. CoSi2, NiSi2, TiSi2

• Semiconducting silicides

e.g. -FeSi2 (bandgap of 0.85 eV), CrSi2 (0.35 eV)and

ReSi2 (0.12 eV).

Advantages of Transition metal silicides

• Temperature stability

• Oxidation resistance

• Low electrical resistivity

FeSiFeSi22-Phases-Phases

Exists in two phases

• Semiconducting low temperature phase

• Metallic high temperature phase

-FeSi2 - FeSi2

~937C

Bandgap of -FeSi2

Quasi direct bandgap

~0.83 eV - ~0.87 eV (at RT)

Nature of bandgap

Optical characterization

• Raman spectroscopy -provides information related to structure

and bonding

Samples investigated

-FeSi2 (undoped)

-(Fe(1-X)Crx)Si2 (x=0.003, 0.01)

-(Fe(1-X)Cox)Si2 (x=0.009, 0.066, 0.14)

Growth method

Molecular beam epitaxy

The deposition can consist of

1.Pure metal deposition at room temp, followed by annealing (SPE)

2.pure metal deposition at high temp (RDE)

3.codeposition of metal and silicon

Raman Spectroscopy

Specifications:

• 0.85m Double monochromator equipped with a pair of 1200 grooves/mm holographic gratings

• 5145 Ar ion laser as excitation source with output power at 300 mW

• Photo multiplier detector tube.

Information obtainable from Raman spectrum

• Raman intensity

• The frequency shift

• The linewidth

Results

Results

Conclusion

• Observed overall red shift if the peaks is related to tensile stress in the samples.

• Tensile stress observed in these samples may result in sufficient strain to cause Y-point transition to become the fundamental direct transition, thus allowing light emission.

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