Amorphous and glassy chalcogenides –

perspective HIGH–TECH MATERIALS with many applications in electronics, optoelectronics, optics, medicine,

chemistry and ecology(FIBERS, MEMORIES, SENSORS, OPTICAL SIGNAL

PROCESSING, …)

Miloslav Frumar, Tomas Wagner, Bozena Frumarova1 and Petr Nemec,

and collaborators, MSc and PhD students 

Research Center and Dep. of General and Inorg. Chemistry, University of Pardubice,

1Joint Laboratory of Solid State Chemistry of Acad. Sci. of Czech Rep. and University of Pardubice, Czech Republic 

 

Frumar Brussels 11 2005 1

Large interest:

               electrical and photoelectrical properties:

photoconductivity, photovoltaics,

         switching effects (treshold and memory) - electrical memories (phase

change, ionic)

bateries, sensors (optical and electrical)

              optics, optoelectronics

infrared optics, optical transmission up to IR (18µm),

optical signal processing, memories, IR luminescence, sensors

              photoinduced phenomena

Photoinduced effects, optical waveguides, optical gratings,

microlenses, planar optical circuits and devices, memories

Frumar Brussels 11 2005 2

Properties – chalcogenide vs. oxide glasses

lower bonding energies

Nonbonding electrons on chalcogen atoms

softer

lower thermal conductivity, low phonon energy

higher electrical conductivity (semiconductors, Eg= 0.3 – 3eV), electrical switching effects, memory materials, phase change, DVD

lower Tg (<0oC - 600oC), lower Tm, optical and electrical memories, good model materials

transparent in the infrared region (~0.8 – 14m for selenides, up to 18 m for tellurides

higher refractive index n (~2.2-3.2), matches with Si, GaAs, ZnSe, InSb and others

High photoinduced ∆n, waveguides production.

high non-linearity in n (optical signal processing)Frumar Brussels 11 2005 3

Frumar Brussels 11 2005 4

intensive luminescence of rare earths RE3+ ions in IR  region, Eu, Er, Nd, Pr, Dy, Sm, …etc., f-f electron transitions,

Light amplification and generation,

IR lasers for tissue coagulation, cutting without bleeding, for tissue excission, removal of arterial plaque, cutting bone and drilling teeth,

eye-safe lasers (radar) at wavelength of ~ 2 μm

chemical sensing and environmental monitoring

light up-conversion, signal couplers, frequency mixing,

High non-linear index of refraction,

The (3) are high in chalcogenides

As2S3 glass: (3) = (1.48 – 2.2) x10-12 esu GeS2 glass, (3) = 1x10-12 esu, SiO2 glass, (3) = 2.8x10-14 (esu) for λ= 1900 nm.

larger (3) lower necessary power and shorter the interaction lengths

possibilty of fully optical signal processing and,

optical computing !!??

If successful: many orders increase of computors speed

Frumar Brussels 11 2005 5

1200 1600 2000 2400 2800 32000

2

4

6

8

10

12

14

Wavelength / nm

Lum

inescence inte

nsity / a

.u.

The luminescence spectrum of the (Ge30Ga5Se65)99.8(Dy2Se3)0.2

glass pumped by 905 nm light.

Frumar Brussels 11 2005 6

The room temperature luminescence spectra of the (Ge30Ga5Se65)99.9(Sm2Se3) 0.1 glass,

excited by 980 nm light (1). The transmittance spectrum is also given (2).

1100 1200 1300 1400 1500 1600

2

4

6

8

10

12

14

16

18

20

Lum

inescence inte

nsity / a

.u.

Wavelength / nm

0

10

20

30

40

50

60

70

80

2

1

Tra

nsm

itta

nce / %

Frumar Brussels 11 2005 7

 Energy scheme of absorption and luminescent transitions of Sm3+ doped glasses

Frumar Brussels 11 2005 8

UNIVERSITY of Pardubice, Czech republic:

chalcogenides: > 30 years, >400 papers, 20 patents

Many aspects:

- Synthesis

- Structure: X ray, Raman, IR, XPS, UPS

– Intrinsic defects (non-stoichiometry, broken bonds, coordination defects, “wrong” bonds, ESR, Raman)

- Extrinsic defects, transition metals, RE3+ ions Bi, Ag, halides,…

- Thin films – vacuum evaporation, spin coating, laser ablation, magnetron sputtering

- Properties: thermal, electrical, optical (VIS, IR), bulk glasses, thin films

Photoinduced changes

RE3+ doped glasses

Pulsed laser ablation

APPLICATION OF GLASSES AND FILMSFrumar Brussels 11 2005 9

Photoinduced changes in amorph. chalcogenides (AC):

Exposure can change

the structure (without or with phase transition)

optical transmittivity and reflectivity

index of refraction

reactivity of the films, the rate of dissolution in chemical solvents production of holographic gratings, very large-resolution lithography (photo-resists for features with size < 0.1 m, optical circuits).

the viscosity

the isotropy - anisotropic effects can be produced.

enhance the diffusion or interdiffusion (metals, Ag, Cu, compounds, Bi2Se3 – Bi2Te3, ..).

induce chemical reactions inside or on the surface of films (e.g. between Ag and chalcogenide film, Bi - Se, )

induce phase changes, e.g.: amorphous-crystalline state Optical and electrical data storage, DVD, etc.

Frumar Brussels 11 2005 10

-many materials studied, e.g. a-Se, As-S, Sb-S, As-Se, As-Te, Sb-Te, Bi-

Te, As-S-Te, Ge-Sb-S, Ge-Ga-S, Ge-Sb-Se, Ge-Sb-Te, Ge-In-Te, Ge-Bi-

Te, Pb-Sb-Se, Pb-Sb-Te, Pb-Bi-Te, etc.,

- all pure and doped,

stoichiometric, non- stoichiometric, thin films, bulk glasses, glassy powders

Thin films - much more disordered more intensive changes

Frumar Brussels 11 2005 11

97As2S3-3Ga2S3As38S62 film

The mechanisms of isotropic irreversible photoinduced changes is relatively well understood

Frumar Brussels 11 2005 12

Exposure or heating increases the rates of chemical reactions among fragments, the film is polymerized and closer to thermodynamic equilibrium.

As4S4 + S2 2As2S3 (1)

 simultaneously photolytic reaction (2)

(2)SSMMTiIihSM ,,

2

Simulation and modelling of these processes:

Frumar Brussels 11 2005 13

Models: structural changes: changes of local bonding configuration, over- under – coordinations, photochemical reactions, crystallization,

│As-As│ + │S-S│ = 2│As-S│ (3)

kTk

SSAsAs

SAsK

exp

2

where ε = 2EAs-S –EAs-As – ES-S (5)

(4)

Frumar Brussels 11 2005 14

The exposure changes also the volume and surface profile

microlenses or microlens arrays can be applied in CCD cameras, imaging machines, optical communication

very high resolution ( 30nm, 5000-10000 lines/mm can be obtained.

Exposure also for holographic recording

Frumar Brussels 11 2005 15

Optically induced dissolution and diffusion of metals in a-chalcogenide films.

The physicochemical processes behind the photodoping were studied.

The changes of optical parameters and chemical reactivity are higher than those of undoped glasses and films.

The photodoped films applied assolid state batteries, ionic sensors

Frumar Brussels 11 2005 16

Diffraction gratings

Frumar Brussels 11 2005 17

Selective optically-induced diffusion and dissolution of silver in a-chalcogenides (no etching)

Frumar Brussels 11 2005 18

INTENSIVE infrared LUMINESCENCE

For high quantum efficiency of luminescence:-low phonon-energies of the glassy matrix:

-the number of phonons to bridge the energy , between electron levels of RE3+ ions, is large → multiphonon relaxation rate is low !

High index of refraction

→ higher values of spontaneous emission probabilities and → larger emission cross-sections of radiative electron transitions between energy levels of RE3+ ions

→ intensive luminescence

Frumar Brussels 11 2005 19

For many applications:

thin films are necessary (planar waveguides, planar circuits, amplifiers, generators)

Laser ablation and the sputtering

- the composition is not practically changed –

all parts of the glass (volatile and non-volatile) are evaporated together

rare–earths elements - less volatile than chalcogenide matrix glasses

→ Thin films can not be prepared by classical vacuum evaporation – similar (identical) Raman spectra = structure

- similar (identical) luminescence spectra

Frumar Brussels 11 2005 20

-     For IR gratings, deep etching is necessary. Sharp edges with height up to 5-10m were obtained

 

The optically induced crystallization or amorphization can be observed in many binary, ternary, more complex, or eutectic compositions

Optical imaging and storage: commercial devices: ternary tellurides are already applied (the change from amorphous to crystalline state and vice versa, 30 nm, DVD - experimentally hundreds of Gb/DVD

Frumar Brussels 11 2005 21

Resently at Pardubice university:

large attention to

•nonvolatile phase change memories,•multilevel nano-size memories

6FP [IST-NMP-3] IST-2004-017406

CHalcogenide MEmory with multiLevel Storage, CAMELS,

with Tech. Univ. Aachen, Politech. Milano, Umicore Lichtenstein, STMicroelectronics Milano

Frumar Brussels 11 2005 22

 

CONCLUSION

Chalcogenide glasses and films

many present and potential applications:

IR, fibers, sensors, bateries, optoelectronics, optical storage

and signal processing, memories, optical computers !?

eye-safe lasers

telecommunications, chemistry, environment, biology,

medicine: e.g. IR lasers for tissue coagulation, cutting without

bleeding, for tissue excision, removal of arterial plaque, cutting bone

and drilling teeth,

Chalcogenides - promising candidates for many applications  

Frumar Brussels 11 2005 23

Thank you for invitation

and for your kind attention !!!

Frumar Brussels 11 2005 24