Measurement of optical properties

1

Light

2

Band structure of semiconductors

3

(000)(111)

conduction

valence

Interband luminescence

Source: ned.ipac.caltech.edu4

(a) Excitation(b) Band-to-band recombination(c) Donor-to-valence band recombination(d) Conductionband-to-acceptor recombination(e) Donor-to-acceptor recombination

5

Raman effect

Stokes Scattering

n0 n0-n

Anti-Stokes Scattering

Raman effect is a 2-photon scattering processThese processes are inelastic scattering:

n0+nn0

No vibration No vibrationVibration Vibration

Photon loses energy Photon gains energy

VibrationalEnergyStates

Virtual Energy States Structure symmetry Lattice dynamics Structural transition

Composition Strain

Electronic states

Inelastic light scattering experiments: Photoluminescence and Raman spectroscopy

7

8

Examples of coherent sources of light

9

Ionization lasersSemiconductor lasers…

Grating spectrometer

Source: wikipedia10

Grating spectrometer

Source: newport11

Beam splitter

12

Beam splitter

13

Laser‐line filter

14

Objective lenses

Magnification, focal length

Numerical aperture: The numerical aperture with respect to a point P depends on the half‐angle θ of the maximum cone of light that can enter or exit the lens.

15

Size of the illumination spot:

. /(Rayleigh criterion)

Sources of luminescence excitation

Cathodo-luminescence

Source: www4.nau.edu17

Experimental details of CL

Source: C.E. Hoffmann, H. A. Atwater, A plasmonic 'bull's‐eye' nanoresonator18

Electronic states in nanostructures

3Dquantization

19

Electronic states in nanostructuresPhotoluminescence and Photoluminescence Excitation (PL, PLE)

20

Excitation range in PL and Raman: 

x

Excitation range in CL: 

C. Trager-Cowan, A. Kean, F. Yang, B. Henderson, and K. P. O’Donnell,Physica B 185, 319 (1993).

Sample structure and theoretical calculations

Experimental results

Increase in resolution?

Increase in resolution?

26

Examples

Defect mapping with CL

27

D2 peak

D4 peak

Si

GaAs(QW)/AlGaAs

Homogeneity of growth

5 nm 4 nm

GaInAs (QW)/InP

Increase in resolution?NSOM: near field optical microscopy

Distance to sample and diameter of aperture smaller than wavelength

. /

Resolution given by aperture size aa

h

a<λ/2n

Increase in resolution?

Raman spectroscopy

• Hematite (‐Fe2O3)

– corundum

• Maghemite(‐Fe2O3)

– spinel

• Magnetite (Fe3O4)

– Inverse spinel

Each polymorph has a characteristic Raman and IR spectrum A. Jub and H. Allen, Appl. Mat. & Interfaces 2, 2804 (2010)

32

Other techniques

Ellipsometry

33http://web.eecs.umich.edu/~fredty/wise2000/jellison.pdf

Ellipsometry

34

One interface Two interfaces

More interfaces: more complicated expressions (matrices used)

Effective medium theory: dielectric function weighted by the different materials forming the layer (including voids)

35

Crystalline silicon with0, 0.8 and 2 nm SiO2

Ellipsometry, examples

36

Ellipsometry, examples

Ellipsometry, examples

37

Ellipsometry, examples

38

FTIR

39

FTIR

40

How to increase signal‐to‐noise ratio: attenuated total reflectance

41

How to increase signal‐to‐noise ratio: attenuated total reflectance

42

Example: ‘smart-cut’

43

Used for the fabrication of Silicon-on-Insulator wafers (SOI)

Example: ‘smart-cut’

44

Used for the fabrication of Silicon-on-Insulator wafers (SOI)

RT

300C

425C

500C

550C

650C

Example: ‘smart-cut’

45

Used for the fabrication of Silicon-on-Insulator wafers (SOI)

Cross-section TEM

Atomic Force Microscopy

RT

Annealed

Example: ‘smart-cut’

46

Used for the fabrication of Silicon-on-Insulator wafers (SOI)

References

47

Ivan Pelant & Jan Valenta, ‘Luminescence Spectroscopy of Semiconductors’ Oxford University press