Transcript Slide 1

UNIVERSITY OF CHEMICAL TECHNOLOGY AND METALLURGY
Optical characterization of As-Se-Me (Me = Ag, Sb) thin films
V. Ilcheva, V. Boev, P. Petkov, T. Petkova
International Conference on Oxide and Non-oxide Materials for Optoelectronics
19 – 22 December 2013, Borovetz
V. Ilcheva
UNIVERSITY OF CHEMICAL TECHNOLOGY AND METALLURGY
Amorphous chalcogenides
fundamental condensed matter research
technological applications
Chalcogenide glasses - (S, Se,Te) + Ge, As, Sb, Ga (elements from IVth, Vth or VIth group )
Properties
disordered structure, compositional dependence of the properties
optical, electrical
photosensitivity
photodarkening, photodoping, photocrystallization
and photoconductivity
design of materials for specific requirements
Characteristics and Advantages
1) Ability of composition variation -> Flexible structure -> Properties modification in desired direction
2) Ability of doping with many different components (elements or compounds)
3) Absence of grain boundaries
4) Isotropic properties
5) High chemical and time stability, radiation durability and nontoxicity
8) Significant ionic conductivity
6) Easy to prepare in bulk and layered form
8) High transparency in the infrared region (~0.8 – 14μm for selenides, up to 18 μm for tellurides)
9) High refractive index n (~2.2-3.2), matches with Si, GaAs, ZnSe, InSb and others
10) High photoinduced ∆n, waveguides production
International Conference on Oxide and Non-oxide Materials for Optoelectronics
19 – 22 December 2013, Borovetz
V. Ilcheva
UNIVERSITY OF CHEMICAL TECHNOLOGY AND METALLURGY
Application
Waveguides
Chalcogenides from the system As-Se (high transmission and high refractive index),
used as a core layer in multilayer planar waveguide structures.
Optical sensors
Planar waveguides
Optical fibers
consist of three layers of materials.
The core is sandwiched between
cladding layers in only one direction.
Light may be confined in the middle layer
by total internal reflection
circular cross-section dielectric waveguides,
consisting of a dielectric material surrounded by
another dielectric material with a lower refractive index.
The core is surrounded by cladding in all transverse directions
based on the change of the light intensity,
after interaction with molecules of different liquids or gasses
Schematic diagram of multilayer film channel
waveguide after deposition and laser writing.
Infrared optics
Optical data storage
Nicolas Ho et al, Opt. Letters, vol. 31, № 12, 2006
International Conference on Oxide and Non-oxide Materials for Optoelectronics
19 – 22 December 2013, Borovetz
V. Ilcheva
UNIVERSITY OF CHEMICAL TECHNOLOGY AND METALLURGY
Optical disks:
DVD+RW - Ag, In, Sb,
DVD-RAM
rewritable CD - Ge, Sn, Sb, Te и Ge, Sn, Sb
Memory devices
(Non volatile memories)
Short laser (current) pulses
local melting
short transitions from crystalline to amorphous state takes place
(reversible phase change structural transitions in the chalcogenide film)
Ncryst. ph. < Nam. ph.; Rcryst. Ph.< Ram. ph..
difference of the opt. (elecrt.) prop. of crystalline and amorphous phase
storage and erasing
Solid state electrolytes in ionic memory
devices (PMC devices)
Phase change materials
The working principle of phase change memories
relies on the contrast in physical properties between
an amorphous and a crystalline phase of the employed
material.
PCRAM
International Conference on Oxide and Non-oxide Materials for Optoelectronics
19 – 22 December 2013, Borovetz
V. Ilcheva
UNIVERSITY OF CHEMICAL TECHNOLOGY AND METALLURGY
Amorphous chalcogenide films
transparent in the infra-red region
of the spectrum
Unique properties
Opportunity for application
photo induced structural changes under
action of light with photon energy
greater than band gaps of the materials.
optical waveguides with different geometry,
applicable in mid-IR fiber-optic sensing.
changes in the optical constants (∆n, ∆k)
and physical-chemical properties
(microhardness, density, solubility).
Planar waveguide
Ncore layer ≠ Ncladding layer - obtained
by illumination with light on the surface of the material.
International Conference on Oxide and Non-oxide Materials for Optoelectronics
19 – 22 December 2013, Borovetz
V. Ilcheva
UNIVERSITY OF CHEMICAL TECHNOLOGY AND METALLURGY
Objective of investigation:
Study of compositional dependence of optical properties in thin
(AsSe)100–xMex films (Me = Ag, Sb), prepared by VTE method.
Study of photoinduced changes in the refractive index after exposure of
the (AsSe)100–xSbx films, realized by Xe lamp illumination.
International Conference on Oxide and Non-oxide Materials for Optoelectronics
19 – 22 December 2013, Borovetz
V. Ilcheva
UNIVERSITY OF CHEMICAL TECHNOLOGY AND METALLURGY
Preparation of thin As-Se-Ag (Sb) films: Vacuum thermal evaporation
COMPOSITIONS
(AsSe)100–xAgx x = 0, 10, 20 mol.% Ag
(AsSe)100–xSbx x = 0, 5, 10, 15 mol.% Sb
CONDITIONS OF VTE PROCESS
source-substrate
distance - 0.12 m
temperature of the substrates - 300 K
residual gas pressure of 10-5 Torr
Thin films for optical measurements:
deposited on glass substrates
d ~ 700 – 1000 nm
International Conference on Oxide and Non-oxide Materials for Optoelectronics
19 – 22 December 2013, Borovetz
V. Ilcheva
UNIVERSITY OF CHEMICAL TECHNOLOGY AND METALLURGY
(AsSe)100–xAgx
100
100
80
T, %
80
60
T, %
60
40
40 x=0 %
x=10 %
20
(AsSe)100–xSbx
20
x=20 %
0
400
600
800
1000
, nm
1200
1400
1600
1800
0
400
x = 15
x = 10
x=5
x=0
600
800
1000
1200
, nm
Red shift of the abs. edge after addition of Ag and Sb is caused by formation of additional defect
states, localized just above the valence band.
Transmission spectra recorded within the spectral range 400 – 2500 nm
International Conference on Oxide and Non-oxide Materials for Optoelectronics
19 – 22 December 2013, Borovetz
V. Ilcheva
UNIVERSITY OF CHEMICAL TECHNOLOGY AND METALLURGY
Refractive index (n) of (AsSe)100-xAgx and (AsSe)100-xSbx films
Swanepoel method could be applied:
weak absorption of the films in the visible region;
k2 << n2; k = αλ/4π; k – extinction coefficient; (n = n – ik)
transparency of the substrate in the visible and near IR
region;
dfilm<<< dsubstrate
n()=2.58+194504/
Refractive index n
n()=2.48+153704/
2,8
20 mol.% Ag
10 mol.% Ag
2,6
n()= 2.74+20117/ , d=1060 nm
2
n()=2.33+196878/
3,0
2
2
2
n()=2.87 + 209018/() , d=1123 nm
3,6
2
n()=2.88 + 245082/ , d=954 nm
2
Refractive index n
3,2
2
n()=3.24 +284603/ , d=666 nm
3,4
15 mol.% Sb
3,2
3,0
10 mol.% Sb
0 mol.% Ag
2,4
600
5 mol.% Sb
0 mol.% Sb
2,8
800
1000
1200
1400
Wavelength, nm
1600
400
800
1200
1600
2000
2400
Wavelength, nm
Spectral dispersion of the refractive index n of amorphous (AsSe)100-xSbx films
nSb containing films> nAg containing films,
n with addition of Ag, Sb
(AsSe)100-xSbx system is selected for further investigation
of it’s optical response under action of light.
International Conference on Oxide and Non-oxide Materials for Optoelectronics
19 – 22 December 2013, Borovetz
V. Ilcheva
UNIVERSITY OF CHEMICAL TECHNOLOGY AND METALLURGY
Transmission, %
100
80
60
40
20
0
80
60
40
20
0
80
60
40
20
0
80
60
40
20
0
unexposed
exposed
(AsSe)85Sb15
600
800
1000
Photobleaching effect is observed after
exposure of the films, realized by Xe lamp
illumination.
(AsSe)90Sb10
Sb decreases the photobleachning effect
600
800
1000
800
1000
800
1000
(AsSe)95Sb5
600
AsSe
600
Wavelength, nm
Transmission spectra recorded within the spectral range 400 – 2500 nm, after irradiation
International Conference on Oxide and Non-oxide Materials for Optoelectronics
19 – 22 December 2013, Borovetz
V. Ilcheva
UNIVERSITY OF CHEMICAL TECHNOLOGY AND METALLURGY
Refractive index (n) of as deposited (AsSe)100-xSbx films
and after Xe lamp illumination - Swanepoel method
3,8
AsSeSb15 virgin
3,6
AsSeSb15 exposed
3,4
3,2
3,2
AsSeSb10 virgin
AsSeSb10 exposed
n
3,0
The increase of n with the addition of Sb is related
to to the structure and to higher polarizability
of larger Sb atoms compared to Se atoms.
2,8
3,2
AsSeSb5 virgin
3,0
AsSeSb5 exposed
decrease of n after illumination.
2,8
3,2
AsSe virgin
AsSe exposed
3,0
2,8
400
800
1200
1600
2000
2400
Wavelength, nm
Spectral dispersion of the refractive index n of amorphous (AsSe)100-xSbx films
International Conference on Oxide and Non-oxide Materials for Optoelectronics
19 – 22 December 2013, Borovetz
V. Ilcheva
UNIVERSITY OF CHEMICAL TECHNOLOGY AND METALLURGY
Conclusions
Thin amorphous (AsSe)100-xMex (Me = Ag, Sb) films are obtained by thermal vacuum evaporation
from the corresponding bulk glassy materials and characterized with respect to their optical
properties.
A red shift of the absorption edge is observed with the addition of Ag and Sb to the glassy matrix.
The refractive index calculations show higher values of this parameter in the Sb-containing
system, which incerases with additon of Sb. This is why this system is selected for further
investigation of it’s optical response under action of light.
Photobleaching effect, as well as refractive index changes are observed after exposure of the films,
realized by Xe lamp illumination.
The obtained results show that the photo-induced structural changes can effectively modify the
refractive index in the exposed region, providing the possibility for creation of planar channels for
integrated optical waveguides.
International Conference on Oxide and Non-oxide Materials for Optoelectronics
19 – 22 December 2013, Borovetz
V. Ilcheva