Introduction
Definition General characteristics Brief history Fabrication
1 Applications of chalcogenide materials
IT Optical memory PRAM Thin film switching device
Chemical sensor Solution- X-ray digital imaging Flexible sensor processed TFT
Energy (chalcogenide)
TE generation Thin film battery FIC Solar cell
commercialized under development
2 Characteristics of chalcogenide materials
resistivity (Wcm ) (PbTe, Ge 2Sb2Te 5) Chalcogenide memory / switch
1018 1010 103 10-1 >10-1 10-8 insulator conductor mobility (cm 2/Vs)
(Ge 2Sb 2Te5, ZnSe , CdTe) Chalcogenide crystalline Si a-Si ZnO TFT 0.1~1 20~30 ~600 1400
bandgap (eV)
(Ge 2Sb 2Te5, CuInSe 2 , CuInGaSe 2, CdTe , CuGaSe 2) Chalcogenide
0.5 0.7 1.0 c-Si a-Si 1.8 solar cell absorption @500~600nm (CdTe, CuInGaSe 2) Chalcogenide
103 c-Si a-Si 105
ionic conduction of Li [S/cm] Polymer gel electrolyte thin film battery LiPON, LiBPO Chalcogenide Liquid electrolyte
10-6 10-5 10-4 10-3 10-2
TE coeff. (mV/K) (n-Bi Te , p-BiSbTe , Pb Ge Se ) Pb 2 3 3 15 37 58 Ca 3Co 4O9 Chalcogenide TE device 4.0 230 Si 440
Processing temp (C)
(SnS(Se ), n -Ge 2Sb2Te 5) flexible device Chalcogenide 500 450 400 350 300 250 200 150
PI_T g: 385 PA_Tg: 330 PES_T g: 228 PC_Tg: 150 3 “Chalcogenides are chameleon compounds: they can be crystalline or amorphous, metallic or semiconducting, and conductors of ions or electrons.”
“Thus, a unified approach to the study of chalcogenides, assessing the roles of atoms, ions and electrons, may prove crucial for both device performance and reliability.” 4 Chalcogenide glass?
Glass consisting of the Group VI elements (S, Se, Te), as major constituents, and others (usually Group IV and/or V elements) 5 Covalent amorphous solids
The chemical bond nature of inorganic glasses Ionic bond: fluoride and halide glasses Covalent bond: chalcogenide glasses (S-, Se-, or Te-based) Metallic bond: amorphous metals Mixed (ionic + covalent) bond: oxide glasses
Relatively strong covalent bonds in ChG Semiconducting but can’t be doped: the empirical 8-N rule Presence of the homopolar bonds Similar electronegativity of constituent atoms Relatively well-defined intermediate range order Presence of (various kinds of) electronic defects
6 Some characteristics of chalcogenide glasses
Good transmittance in the infrared region (~20 mm) IR optical devices Low phonon energy (~200 cm-1 for selenide glass) Host for ion-doped laser and amplifier (3) 3 High c optical nonlinearity (~10 higher than a-SiO2) Ultrafast all optical switching for optical communications Semiconducting Photocopying machines, digital x-ray imaging, PCM Fast ion conducting Thin film battery, ionics devices Photo-induced phenomena Photolithography, Optical waveguide
7 Classification Amorphous covalent solid Glassy semiconductor Lone-pair semiconductor
Strong covalent glass Obeying the 8-N rule Ge, Si, As, Sb… Electronic conductor
Weak covalent glass Violating the 8-N rule Ga, In, Na, Ag… Ionic conductor
Bulk or film? * Figure taken from K. Tanaka, Optoelectronic Mater. Devices 1 (2004) 43.
8 Surface of fresh cut of glass vs freshly deposited thin film
14000 As S bulk 21000 2 3 As S bulk As3d core level 2 3 12000 18000 S 2p core level 10000 15000 8000 12000
Counts 6000 9000 Counts 4000 6000 2000 3000 0 0 46 45 44 43 42 41 165 164 163 162 161 160 Binding energy, eV Binding energy, eV
Bulk As2S3
7000 10000 6000 As 3d S2p 16 % within S-S 8000 84 % AsS 5000 3/2 AsS 4000 3/2 6000 3000
Counts As-As Counts 2000 4000 1000
2000 0 165 164 163 162 161 45 44 43 42 41 Binding energy (eV) Binding energy (eV)
* Slide provided by Dr A. Kovalskiy Freshly deposited As2S3 film 9 Chemical bonds
* K. Tanaka, Optoelectronic Mater. Devices 1 (2004) 43. 10 Brief history The earliest experimental data on an oxygen-free glass have been published by Schulz-Sellack in 1870 [1]. Later on, Wood in 1902 [2], as well as Meier in 1910 [3] carried out the first researches on the optical properties of vitreous selenium. In 1950, Frerichs [4] published the paper: “New optical glasses transparent in infrared up to 12 mm” Glaze and co-workers [5] developed in 1957 the first method for the preparation of the glass at the industrial scale. Winter-Klein [6] published reports on numerous chalcogenides prepared in the vitreous state. A research group lead by Kolomiets and Goriunova discovered the first
semiconducting glass, TlAsSe2 [7]. In 1968, Ovshinsky [8] discovered the memory and switching effects of some chalcogenide glasses.
1. C. Shultz-Sellack, Ann. Phys. 139, 182 (1870). 2. R. W. Wood, Phil. Mag. 3, 607 (1902). 3. W. Meier, Ann. Phys. 31, 1017 (1910). 4. R. Frerichs, Phys. Rev. 78, 643 (1950). 5. F. W. Glaze, D. H. Blackburn, J. S. Osmalov, D. Hubbard, M. H. Black, J. Res. Nat. Bur. Standards 59, 83 (1957). 6. A. Winter-Klein, Verres et Refractaires 9, 147 (1955). 7. N. A. Goriunova, B. T. Kolomiets, Zhurnal Tekhnicheskoi Fiziki (Russ.) 25, 2069 (1955). 8. S. R. Ovshinsky, Phys. Rev. Lett. 21, 1450 (1968) 11 12 The material used: amorphous AsSiGeTe
13 Fabrication Melt-quenching
* Photo provided by D. Zhao * Feltz book, p. 16.
14 Low-temp. wet process Solution process
15 Low-temp. wet process Sol-gel
* Feltz book, p. 19.
16 PVD (Evaporation) Thermal and/or e-beam
* Feltz book, p. 22. 17 PVD (Sputtering) DC or RF magnetron
* Feltz book, p. 25. 18 PVD (PLD) Laser ablation
19 Mechanical milling
20