Abstract
The films containing Ge nanoparticles embedded in SiO2 matrix were prepared by RF magnetron sputtering and subsequently by thermal annealing. Their structure was investigated by conventional transmission electron microscopy and high resolution transmission electron microscopy together with energy-dispersive X-ray spectroscopy. The electrical behavior of films was studied by measuring current–temperature and current–voltage characteristics. The structure investigation reveals two kinds of features: a low density of big Ge nanoparticles with sizes from 20 to 50 nm and a network of small amorphous Ge nanoregions/nanoparticles (5 nm size or less) with high density, both being embedded in amorphous SiO2 matrix. The electrical transport was shown to take place through the network of amorphous Ge nanoregions. At low temperature, the T −1/4 dependence of the current was evidenced, while at high temperature, the T −1 Arrhenius dependence was found. At both low and high temperatures, the conductivity is nearly constant. The behavior at low temperature was explained by the hopping mechanism on localized states located in a band near the Fermi energy, while at high temperature by the charge excitation to the extended states.
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References
Ahmed AHZ, Tait RN (2003) Characterization of amorphous GexSi1−xOy for micro machined uncooled bolometer applications. J Appl Phys 94:5326–5332. doi:10.1063/1.1609633
Aktağ A, Yilmaz E, Mogaddam NAP, Aygün G, Cantas A, Turan R (2010) Ge nanocrystals embedded in SiO2 in MOS based radiation sensors. Nucl Instr Methods Phys Res B 268:3417–3420. doi:10.1016/j.nimb.2010.09.007
Basa P, Alagoz AS, Lohner T, Kulakci M, Turan R, Nagy K, Horváth ZsJ (2008) Electrical and ellipsometry study of sputtered SiO2 structures with embedded Ge nanocrystals. Appl Surf Sci 254:3626–3629. doi:10.1016/j.apsusc.2007.10.075
Beyer V, von Borany J, Klimenkov M (2007) A transient electrical model of charging for Ge nanocrystal containing gate oxides. J Appl Phys 101:094507. doi:10.1063/1.2723864
Chen WR, Chang TC, Liu PT, Tu CH, Yeh JL, Hsieh YT, Wang RY, Chang CY (2007) Formation of germanium nanocrystals by rapid thermal oxidizing SiGeO layer for nonvolatile memory application. Surf Coat Tech 202:1333–1337. doi:10.1016/j.surfcoat.2007.07.112
Chew HG, Choi WK, Foo YL, Zheng F, Chim WK, Voon ZJ, Seow KC, Fitzgerald EA, Lai DMY (2006) Effect of germanium concentration and oxide diffusion barrier on the formation and distribution of germanium nanocrystals in silicon oxide matrix. Nanotechnology 17:1964–1968. doi:10.1088/0957-4484/17/8/028
Chew HG, Zheng F, Choi WK, Chim WK, Foo YL, Fitzgerald EA (2007) Influence of reductant and germanium concentration on the growth and stress development of germanium nanocrystals in silicon oxide matrix. Nanotechnology 18:065302. doi:10.1088/0957-4484/18/6/065302
Choi WK, Ng V, Ng SP, Thio HH, Shen ZX, Li WS (1999) Raman characterization of germanium nanocrystals in amorphous silicon oxide films synthesized by rapid thermal annealing. J Appl Phys 86:1398–1403. doi:10.1063/1.370901
Choi WK, Ho YW, Ng SP, Ng V (2001) Microstructural and photoluminescence studies of germanium nanocrystals in amorphous silicon oxide films. J Appl Phys 89:2168–2172. doi:10.1063/1.1342026
Choi WK, Chew HG, Hob V, Ng V, Chim WK, Ho YW, Ng SP (2006a) Formation of germanium nanocrystals in thick silicon oxide matrix on silicon substrate under rapid thermal annealing. J Cryst Growth 288:79–83. doi:10.1016/j.jcrysgro.2005.12.033
Choi WK, Chew HG, Zheng F, Chim WK, Foo YL, Fitzgerald EA (2006b) Stress development of germanium nanocrystals in silicon oxide matrix. Appl Phys Lett 89:113126. doi:10.1063/1.2354012
Ciurea ML, Lazanu S, Stavarache I, Lepadatu AM, Iancu V, Mitroi MR, Nigmatullin RR, Baleanu CM (2011) Stress-induced traps in multilayered structures. J Appl Phys 109:013717. doi:10.1063/1.3525582
Coppari F, Chervin JC, Congeduti A, Lazzeri M, Polian A, Principi E, Di Cicco A (2009) Pressure-induced phase transitions in amorphous and metastable crystalline germanium by Raman scattering X-ray spectroscopy, and ab initio calculations. Phys Rev B 80:115213. doi:10.1103/PhysRevB.80.115213
Cosentino S, Liu P, Le ST, Lee S, Paine D, Zaslavsky A, Pacifici D, Mirabella S, Miritello M, Crupi I, Terrasi A (2011a) High-efficiency silicon-compatible photo detectors based on Ge quantum dots. Appl Phys Lett 9:221107. doi:10.1063/1.3597360
Cosentino S, Mirabella S, Miritello M, Nicotra G, Lo Savio R (2011b) The role of the surfaces in the photon absorption in Ge nanoclusters embedded in silica. Nanoscale Res Lett 6:135. doi:10.1186/1556-276X-6-135
Elliott PJ, Yoffe AD, Davis EA (1974) Hopping conduction in amorphous germanium. AIP Conf Proc 20:311–319. doi:10.1063/1.2945979
Fujii M, Inoue Y, Shinji H, Yamamoto K (1996) Hopping conduction in SiO2 films containing C, Si, and Ge clusters. Appl Phys Lett 68:3749–3751. doi:10.1063/1.115994
Fujii M, Mamezaki O, Hayashi S, Yamamoto K (1998) Current transport properties of SiO2 films containing Ge nanocrystals. J Appl Phys 83:1507–1512. doi:10.1063/1.366858
Gao F, Green MA, Conibeer G, Cho EC, Huang Y, Pere-Wurfl I, Flynn C (2008) Fabrication of multilayered Ge nanocrystals by magnetron sputtering and annealing. Nanotechnology 19:455611. doi:10.1088/0957-4484/19/45/455611
Godet C (2001) Hopping model for charge transport in amorphous carbon. Philos Mag B 81:205–222. doi:10.1080/13642810108216536
Iancu V, Draghici M, Jdira L, Ciurea ML (2004) Conduction mechanisms in silicon-based nano composites. J Optoelectron Adv Mater 6:53–56
Inoue Y, Fujii M, Hayashi S, Yamamoto K (1998) Single electron tunneling through Ge nanocrystal fabricated by cosputtering method. Solid-State Electron 42:1605–1608. doi:10.1016/S0038-1101(98)00079-3
Jensen JS, Leervad Pedersen TP, Pereira R, Chevallier J, Lundsgaard Hansen J, Bech Nielsen B, Nylandsted Larsen A (2006) Ge nanocrystals in magnetron sputtered SiO2. Appl Phys A 83:41–48. doi:10.1007/s00339-005-3479-7
Jie Y, Wee ATS, Huan CHA, Shen ZX, Choi WK (2011) Phonon confinement in Ge nanocrystals in silicon oxide matrix. J Appl Phys 109:033107. doi:10.1063/1.3503444
Kolobov AV, Wei SQ, Yan WS, Oyanagi H, Maeda Y, Tanaka K (2003) Formation of Ge nanocrystals embedded in a SiO2 matrix: transmission electron microscopy, X-ray absorption, and optical studies. Phys Rev B 67:195314. doi:10.1103/PhysRevB.67.195314
Lepadatu AM, Stavarache I, Stoica TF, Ciurea ML (2011) Study of Ge nanoparticles embedded in an amorphous SiO2 matrix with photoconductive properties. Dig J Nanomater Bios 6:67–73
Li J, Wu XL, Hu DS, Yang YM, Qiu T, Shen JC (2004) Splitting of X-ray diffraction peak in (Ge:SiO2)/SiO2 multi layers. Solid State Commun 131:21–25. doi:10.1016/j.ssc.2004.04.026
Lomas RA, Hampshire MJ, Tomlinson RD, Knott KF (1973) Hall effects and noise measurement in epitaxial, polycrystalline, and amorphous Ge. Phys Stat Sol (a) 16:385–394. doi:10.1002/pssa.2210160206
Maeda Y (1995) Visible photoluminescence from nano crystallite Ge embedded in a glassy SiO2 matrix: evidence in support of the quantum-confinement mechanism. Phys Rev B 51:1658–1670. doi:10.1103/PhysRevB.51.1658
Mott NF (1969) Conduction in non-crystalline materials. III. Localized states in pseudogap and near extremities of conduction and valence bands. Philos Mag 19:835–852. doi:10.1080/14786436908216338
Peibst R, Erenburg M, Bugiel E, Hofmann KR (2010) Effects influencing electron and hole retention times in Ge nanocrystal memory structures operating in the direct tunneling regime. J Appl Phys 108:054316. doi:10.1063/1.3467527
Pinto SRC, Rolo AG, Buljan M, Chahboun A, Bernstorff S, Barradas NP, Alves E, Kashtiban RJ, Bangert U, Gomes MJM (2011) Low-temperature fabrication of layered self-organized Ge clusters by RF-sputtering. Nanoscale Res Lett 6:341. doi:10.1186/1556-276X-6-341
Pollak M, Knotek ML, Kurtzman H, Glick H (1973) DC conductivity of amorphous germanium and the structure of the pseudogap. Phys Rev Lett 30:856–859. doi:10.1103/PhysRevLett.30.856
Ray SK, Das K (2005) Luminescence characteristics of Ge nanocrystals embedded in SiO2 matrix. Opt Mater 27:948–952. doi:10.1016/j.optmat.2004.08.041
Shen JK, Wu XL, Tan C, Yuan RK, Bao XM (2002) Correlation of electroluminescence with Ge nanocrystal sizes in Ge-SiO2 co-sputtered films. Phys Lett A 300:307–310. doi:10.1016/S0375-9601(02)00617-5
Srinivasa Rao N, Pathak AP, Devaraju G, Saikiran V (2011) Growth and characterization of nc-Ge prepared by microwave annealing. Vacuum 85:927–931. doi:10.1016/j.vacuum.2011.01.012
Stavarache I, Lepadatu AM, Gheorghe NG, Costescu RM, Stan GE, Marcov D, Slav A, Iordache G, Stoica TF, Iancu V, Teodorescu VS, Teodorescu CM, Ciurea ML (2011) Structural investigations of Ge nanoparticles embedded in an amorphous SiO2 matrix. J Nanopart Res 13:221–232. doi:10.1007/s11051-010-0021-4
Takeoka S, Fujii M, Hayashi S, Yamamoto K (1998) Size-dependent near-infrared photoluminescence from Ge nanocrystals embedded in SiO2 matrices. Phys Rev B 58:7921–7925. doi:10.1103/PhysRevB.58.7921
Teodorescu VS, Ciurea ML, Iancu V, Blanchin MG (2008) Morphology of Si nano crystallites embedded in SiO2 matrix. J Mater Res 23:2990–2995. doi:10.1557/jmr.2008.0358
Tzeng SS, Li PW (2008) Enhanced 400–600 nm photo responsivity of metal-oxide-semiconductor diodes with multi-stack germanium quantum dots. Nanotechnology 19(235203):1–6. doi:10.1088/0957-4484/19/23/235203
Zhang B, Shrestha S, Green MA, Conibeer G (2010a) Size controlled synthesis of Ge nanocrystals in SiO2 at temperatures below 400 °C using magnetron sputtering. Appl Phys Lett 96:261901. doi:10.1063/1.3457864
Zhang B, Shrestha S, Green MA, Conibeer G (2010b) Surface states induced high P-type conductivity in nano structured thin film composed of Ge nanocrystals in SiO2 matrix. Appl Phys Lett 97:132109. doi:10.1063/1.3496031
Zhang B, Yao Y, Patterson R, Shrestha S, Green MA, Conibeer G (2011) Electrical properties of conductive Ge nanocrystal thin films fabricated by low temperature in situ growth. Nanotechnology 22:125204. doi:10.1088/0957-4484/22/12/125204
Zhao J, Rebohle L, Gebel T, von Borany J, Skorupa W (2002) Bulk-limited conduction of Ge-implanted thermally grown SiO2 layers. Solid-State Electron 46:661–664. doi:10.1016/S0038-1101(01)00322-7
Zhen C, Liu Y, Ma L, Pang Z, Pan C, Hou D (2010) Ferromagnetism in Ge/SiO2 multilayer films. J Appl Phys 107:043901. doi:10.1063/1.3294621
Zheng F, Choi WK, Lin F, Tripathy S, Zhang JX (2008) Stress tuning of Ge nanocrystals embedded in dielectrics. J Phys Chem C 112:9223–9228. doi:10.1021/jp801529j
Acknowledgments
This work was supported from Project No. 471/2009 (ID 918/2008), Ideas Program, National Research, Development and Innovation Plan 2007–2013.
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Stavarache, I., Lepadatu, AM., Maraloiu, A.V. et al. Structure and electrical transport in films of Ge nanoparticles embedded in SiO2 matrix. J Nanopart Res 14, 930 (2012). https://doi.org/10.1007/s11051-012-0930-5
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DOI: https://doi.org/10.1007/s11051-012-0930-5