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Mar 09, 2024 164 likes •282 views

Amorphous silicon PVMD Arno Smets Delft University of Technology Learning objectives What is amorphous silicon What are the different types of defects in a-Si How does the amorphous structure affect the material properties

SLIDE 1

PVMD

Delft University of Technology

Amorphous silicon

Arno Smets

SLIDE 2

Learning objectives

What is amorphous silicon
What are the different types of defects in a-Si
How does the amorphous structure affect the

material properties

SLIDE 3

Source: www.youtube.com/watch?v=OyVUmucwhPo

SLIDE 4

Amorphous silicon

Si atom Covalent bond Unpassivated dangling bond Hydrogen passivated dangling bond Single crystal silicon Hydrogenated amorphous silicon a-Si

Defect density: c-Si a-Si a-Si:H

:H

1012-14 cm3 1019 cm3 1016 cm3

SLIDE 5

Defects in a-Si:H

SLIDE 6

Band diagram

EV EC E EG Conduction band Valence band Band gap

SLIDE 7

EC g(E) EV,mob EC,mob EV E

Defect states Valence band tail Conduction band tail

Emob =1.8 eV direct EG =1.1 eV indirect

Band diagram

gV gC

SLIDE 8

EC gC g(E) gV Emob=1.8 eV EV,mob EC,mob EV E EG=1.1 eV

Defect states conduction band tail

direct indirect c-Si: Indirect bandgap EG=1.1 eV a-Si: Direct bandgap Emob=1.8 eV

Band diagram

SLIDE 9

c-Si

Absorption coefficient

a-Si c-Si

Wavelength (nm) 827 1240 2480 620 496 413 Absorption coefficient (cm-1) 100 101 102 103 104 105

a-Si

Photon energy (eV) 0.5 1.0 1.5 2.0 2.5 3.0

c-Si: Indirect bandgap EG=1.1 eV a-Si: Direct bandgap Emob=1.8 eV

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c-Si a-Si

Indirect bandgap EG=1.1 eV Direct bandgap Emob=1.8 eV

EC g(E) EV E gV gC EG g(E) EV,mob EC,mob E Emob g

gC gV