Method for passivating at least a part of a substrate surface

A method for passivating at least a part of a surface of a semiconductor substrate, wherein at least one layer comprising at least one a-Si:H passivation layer is realized on said part of the substrate surface by: - generating a plasma (P) by means of at least one plasma source (3) mounted on the process chamber (5) at a distance (L) from the substrate surface, at least part of the plasma (P) being injected into the chamber (5) and achieving a supersonic speed; - contacting at least a part of the plasma (P), injected into the chamber (5), with the said part of the substrate surface; and - supplying at least one precursor suitable for passivation layer realization to the said part of the plasma (P) via a plurality of injection nozzles (19) of an injector device (17), such that the density of the precursor at each injection nozzle (19) is lower than 12x1022 particles/m3

Sign reversal of spin polarization in Co/Ru/Al2O3/Co magnetic tunnel junctions

Utilizing ultrathin Ru interfacial layers in Co/Al2O3/Co tunnel junctions, we demonstrate that not only does the tunnel magnetoresistance decrease strongly as the Ru thickness increases as found for Cu or Cr interlayers, in contrast, even the sign of the apparent tunneling spin polarization may be changed. Further, the magnitude and sign of the apparent polarization is strongly dependent on applied voltage. The results are explained by a strong density-of-states modification at the (interdiffused) Co/Ru interface, consistent with theoretical calculations and experiments on Co/Ru metallic multilayers and Co-Ru alloys

Silicon surface passivation by hot-wire CVD Si thin films studied in situ surface spectroscopy

Silicon thin films can provide an excellent surface passivation of crystalline silicon (c-Si) which is of importance for high efficiency heterojunction solar cells or diffused emitter solar cells with well-passivated rear surfaces. Hot-wire chemical vapor deposition (hotwire CVD) is an attractive method to synthesize Si thin films for these applications as the method is ion-bombardment free yielding good quality films over a wide range of deposition rates. The properties of the interface between Si thin films and H-terminated c-Si substrates have been studied during film growth by three complementary in situ techniques. Spectroscopic ellipsometry has been used to determine the optical properties, film thickness and surface roughness whereas information on the H-bonding modes and H-depth profile has been obtained by attenuated total reflection infrared spectroscopy. Second-harmonic generation (SHG), a nonlinear optical technique sensitive to surface and interface states, has been used to probe two-photon resonances related to modified Si-Si bonds at the interface. The observations have been correlated with ex situ lifetime spectroscopy experiments. On the basis of the results, the growth and surface passivation mechanism of the films will be discussed, including the role of defect states, built-in electric fields, (nanometer-level) epitaxial growth, influence of the substrate temperature, etc

Real-time study of α-Si:H/c-Si heterointerface formation and epitaxial Si growth by spectroscopic ellipsometry, infrared spectroscopy, and second-harmonic generation

The performance of many devices based on Si thin films deposited on crystalline Si (c-Si) 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 Si(100) substrates. The formation of hydrogenated amorphous Si (a-Si:H), 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 (SHG) has been applied both spectroscopically and in real time. The SHG spectra of a-Si:H films on Si(100) 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/E1 critical point (CP) 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 growt