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Negative charge and charging dynamics in Al2O3 films on Si characterized by second-harmonic generation.

Document VersionPublisher's PDF, also known as Version of Record (includes final page, issue and volume numbers) Please check the document version of this publication:• A submitted manuscript is the author's version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. People interested in the research are advised to contact the author for the final version of the publication, or visit the DOI to the publisher's website.• The final author version and the galley proof are versions of the publication after peer review.• The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal ? Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. The surface and interface sensitive nonlinear optical technique of second-harmonic generation ͑SHG͒ is a very useful diagnostic in studying surface and interface properties in thin film systems and can provide relevant information during thin film processing. An important aspect when applying SHG is the interpretation of the SHG response. In order to utilize the full potential of SHG during materials processing it is necessary to have a good understanding of both the macroscopic and the microscopic origin of the SHG response, particularly in thin film or multilayer systems where the propagation of radiation is another important aspect that should be considered carefully. A brief theoretical overview on the origin of the SHG response and a description of the propagation of radiation will be given. Furthermore, several methods will be discussed that might reveal the possible macroscopic and microscopic origins of the SHG response in thin film systems. The different approaches will be illustrated by examples of real-time and spectroscopic SHG experiments with thin film systems relevant in Si etching and deposition environments, such as ͑1͒ hydrogenated amorphous Si films deposited by hot-wire chemical vapor deposition on both Si͑100͒ and fused silica substrates, ͑2͒ amorphous Si generated by low-energy Ar + -ion bombardment of H terminated Si͑100͒, and ͑3͒ Al 2 O 3 films deposited by plasma-assisted atomic layer deposition on H terminated Si͑100͒.

The performance of many devices based on Si thin films deposited on crystalline Si ͑c-Si͒ is highly governed by interface quality. For many of these applications, only fully epitaxial films or fully amorphous films having an abrupt interface with the substrate are desired. However, the realization of these perfectly sharp interfaces and the mechanisms governing their formation are not fully understood yet. In this study, the interface formation between Si thin films and c-Si has been investigated by simultaneously applying three complementary optical techniques in real time during low temperature Si film growth. The films were deposited in a hot-wire chemical vapor deposition process by using both native oxide covered and H terminated Si͑100͒ substrates. The formation of hydrogenated amorphous Si ͑a-Si: H͒, epitaxial Si, and mixed phase Si has been detected with spectroscopic ellipsometry by measuring the optical properties of the growing films. The evolution of the hydrogen content and hydrogen bonding configurations in the films has been monitored by attenuated total reflection infrared spectroscopy. A clear dependence of the hydrogen content on film morphology is observed with the amorphous films containing significantly more hydrogen. The surface and interface sensitive technique of second-harmonic generation ͑SHG͒ has been applied both spectroscopically and in real time. The SHG spectra of a-Si:H films on Si͑100͒ obtained in the SHG photon energy range of 2.7-3.5 eV revealed a dominant contribution originating from the film/substrate interface related to E 0 Ј/E 1 critical point ͑CP͒ transitions of c-Si. The real-time behavior of the SHG response is shown to strongly depend on differences in initial film morphology, which allows for identification of direct a-Si: H / c-Si heterointerface formation, nanometer-level epitaxial growth, and fully epitaxial growth at a very early stage of film growth. On the basis of the results obtained by the three optical techniques, the c-Si surface passivation mechanism by a-Si: H thin films is addressed and it is demonstrated that the combination of the techniques provides a profound method to control processes occurring during Si thin film growth.

The nucleation behavior of supersaturated water vapor in helium is experimentally investigated in the temperature range of 200-240 K. The experiments are performed using a pulse expansion wave tube. The experimental results show a sharp transition in the nucleation rates at 207 K. We suggest that the transition is due to the transition of vapor/liquid to vapor/solid nucleation ͑ordered with decreasing temperature͒. A qualitative theoretical explanation is given based on the classical nucleation theory and the surface energy of ice.