Please note, due to essential maintenance online transactions will not be possible between 02:30 and 04:00 BST, on Tuesday 17th September 2019 (22:30-00:00 EDT, 17 Sep, 2019). We apologise for any inconvenience.
To send content items to your account,
please confirm that you agree to abide by our usage policies.
If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account.
Find out more about sending content to .
To send content items to your Kindle, first ensure email@example.com
is added to your Approved Personal Document E-mail List under your Personal Document Settings
on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part
of your Kindle email address below.
Find out more about sending to your Kindle.
Note you can select to send to either the @free.kindle.com or @kindle.com variations.
‘@free.kindle.com’ emails are free but can only be sent to your device when it is connected to wi-fi.
‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
Thin films of amorphous silicon with nanocrystalline silicon inclusions are fabricated using a dual plasma PECVD co-deposition system. Raman spectroscopy and X-ray diffraction confirmed the crystallinity of the embedded nanocrystals as well as their diameter, which is varied from 4.3 nm to 17.5 nm. The dark conductivity of the films is highly dependent on the crystal fraction, with a maximum room temperature conductivity found for a crystal concentration of 5.5%, well below the percolation threshold. Proton irradiation at energies of 217 MeV with a total fluence of 5 x1012 protons/cm2 caused no significant radiation damage. The enhancement of the conductivity, along with the absence of radiation damage suggests this material may be a candidate for use in the next generation of particle detectors in the Compact Muon Solenoid in the Large Hadron Collider at CERN.
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-SiNx:H film.
The conductivity of amorphous/nanocrystalline hydrogenated silicon thin films (a/nc-Si:H) deposited in a dual chamber co-deposition system exhibits a non-monotonic dependence on the nanocrystal concentration. Optical absorption measurements derived from the constant photocurrent method (CPM) and preliminary electron spin resonance (ESR) data for similarly prepared materials are reported. The optical absorption spectra, in particular the subgap absorption, are found to be independent of nanocrystalline density for relatively small crystal fractions (< 4%). For films with a higher crystalline content, the absorption spectra indicate broader Urbach slopes and higher midgap absorption. The ESR spectra show an approximately constant defect density across all of the films. These data are interpreted in terms of a model involving electron donation from the nanocrystals into the amorphous material.
The production of hydrogenated amorphous silicon films containing silicon nanocrystal-line inclusions (a/nc-Si:H) is demonstrated using a new deposition process. Crystalline Si nanoparticles around 5 nm in diameter are generated in a flow-through plasma reactor, and are introduced into a downstream capacitively-coupled plasma enhanced chemical vapor deposition reactor where the particles are “co-deposited” with the amorphous phase of the film. Transmis-sion electron microscopy confirms the presence of crystalline inclusions in these films, as well as providing confirmation that the crystalline particles are indeed produced in the flow-through re-actor and not in the capacitive plasma. Electrical measurements indicate an improvement in the dark conductivity of the intrinsic a/nc-Si:H films as the particle concentration is increased, sug-gesting that the particles have a doping effect on the films charge transport properties.
The Seebeck coefficient and dark conductivity for undoped, and n-type doped thin film hydrogenated amorphous silicon (a-Si:H), and mixed-phase films with silicon nanocrystalline inclusions (a/nc-Si:H) are reported. For both undoped a-Si:H and undoped a/nc-Si:H films, the dark conductivity is enhanced by the addition of silicon nanocrystals. The thermopower of the undoped a/nc-Si:H has a lower Seebeck coefficient, and similar temperature dependence, to that observed for undoped a-Si:H. In contrast, the addition of nanoparticles in doped a/nc-Si:H thin films leads to a negative Seebeck coefficient (consistent with n-type doping) with a positive temperature dependence, that is, the Seebeck coefficient becomes larger at higher temperatures. The temperature dependence of the thermopower of the doped a/nc-Si:H is similar to that observed in unhydrogenated a-Si grown by sputtering or following high-temperature annealing of a-Si:H, suggesting that charge transport may occur via hopping in these materials.
Email your librarian or administrator to recommend adding this to your organisation's collection.