Electronic transport in doped mixed-phase hydrogenated amorphous/nanocrystalline silicon thin films

Wienkes, Lee; Blackwell, C.; Kakalios, J.

doi:10.1063/1.3685491

Cited by 21 publications

(17 citation statements)

References 23 publications

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“…Specifically, as the average number ν of dopant electrons per NC is varied, the dependence of the resistivity ρ on the temperature T changes between Arrhenius-type activated conduction (γ = 1) and VRH (γ < 1). VRH has been reported in a variety of granular semiconductor systems [2,7,13,14], but thus far there is no general theory to explain how these different types of conduction can coexist and why they appear in particular ranges of the electron "filling factor" ν.…”

Section: Introductionmentioning

confidence: 99%

Theory of hopping conduction in arrays of doped semiconductor nanocrystals

2012

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The resistivity of a dense crystalline array of semiconductor nanocrystals (NCs) depends in a sensitive way on the level of doping as well as on the NC size and spacing. The choice of these parameters determines whether electron conduction through the array will be characterized by activated nearest-neighbor hopping or variable-range hopping (VRH). Thus far, no general theory exists to explain how these different behaviors arise at different doping levels and for different types of NCs. In this paper we examine a simple theoretical model of an array of doped semiconductor NCs that can explain the transition from activated transport to VRH. We show that in sufficiently small NCs, the fluctuations in donor number from one NC to another provide sufficient disorder to produce charging of some NCs, as electrons are driven to vacate higher shells of the quantum confinement energy spectrum. This confinement-driven charging produces a disordered Coulomb landscape throughout the array and leads to VRH at low temperature. We use a simple computer simulation to identify different regimes of conduction in the space of temperature, doping level, and NC diameter. We also discuss the implications of our results for large NCs with external impurity charges and for NCs that are gated electrochemically.

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Section: Introductionmentioning

confidence: 99%

Theory of hopping conduction in arrays of doped semiconductor nanocrystals

2012

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“…This is the well known "thermal equilibration effect" observed in doped a-Si:H [22,23]. The presence of the nanocrystallites has been found to lead to slower stretched exponential relaxation and a reduction in the difference in the conductivity between the slow cool and rapid quench states, consistent with slower hydrogen diffusion in the a/nc-Si:H films [24].…”

Section: N-type Doped A/nc-si:h Filmsmentioning

confidence: 81%

Opto-electronic properties of co-deposited mixed-phase hydrogenated amorphous/nanocrystalline silicon thin films

et al. 2011

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Mixed-phase thin film materials, consisting of nanocrystalline semiconductors embedded within a bulk semiconductor or insulator, have been synthesized in a dual-chamber co-deposition system. A flow-through plasma reactor is employed to generate nanocrystalline particles, that are then injected into a second, capacitively-coupled plasma deposition system in which the surrounding semiconductor or insulating material is deposited. Raman spectroscopy, X-ray diffraction and high resolution TEM confirm the presence of nanocrystals homogenously embedded throughout the a-Si:H matrix. In undoped nc-Si within a-Si:H (a/nc-Si:H), the dark conductivity increases with crystal fraction, with the largest enhancement of several orders of magnitude observed when the nanocrystalline density corresponds to a crystalline fraction of 2 -4%. These results are consistent with the nc donating electrons to the surrounding a-Si:H matrix without a corresponding increase in dangling bond density for these films. In contrast, charge transport in n-type doped a/nc-Si:H films is consistent with multi-phonon hopping, possibly through extended nanocrystallite clusters with weak electron-phonon coupling. The flexibility of the dual-chamber co-deposition process is demonstrated by the synthesis of mixed-phase thin films comprised of two distinct chemical species, such as germanium nanocrystallites embedded in a-Si:H and Si nanocrystallites embedded within an insulating a-SiN x :H film.

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“…The conductivity as well as the photoconductivity of hydrogenated a-Si thin films containing nanocrystalline Si (nc-Si) inclusions is known to decrease when f is reduced (see Ref. [14][15][16][17][18] and references therein). The measured conductivities of the MQW cells obtained from the linear I-V curves in the 4th quadrant show the same trend: (4,17 ± 0:81) × 10 -7 (Ω cm) -1 for the 4 nm MQW device (f = 33 %) and (6:15 ± 0:63) × 10 -8 (Ω cm) -1 for the 4 nm MQW device (f = 11 %).…”

Section: Resultsmentioning

confidence: 99%