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- atomic layer deposition (2)
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Institute
The passivation of n-type InP (100) using sulfur in combination with a gadolinium aluminate (GAO) dielectric layer has been studied. Photoluminescence, minority-carrier lifetime, and capacitance−voltage measurements indicate that a (NH4)2S vapor passivation step prior to atomic layer deposition of the oxide effectively lowers the interface state density. Surface and interface chemistry were studied by synchrotron radiation photoemission spectroscopy (SRPES). The effect of ex situ surface passivation after native oxide removal in HCl solution was examined. It was observed that surface reoxidation occurred during (NH4)2S vapor exposure, leading to the formation of Inx(HPO4)y. S was present on the surface as a sulfide in both surface and subsurface sites. After atomic layer deposition of GAO, sulfates were detected in addition to Inx(HPO4)y, which was confirmed by near-edge X-ray absorptionfine structure analysis. The S in the stack was quantified using reference-free grazing incidence X-rayfluorescence
analysis. X-ray absorption spectroscopy showed that Gd was oxidized and present in the 3+ oxidation state, most likely as a phosphate close to the InP interface and possibly mixed with sulfates. Energy-dependent SRPES measurements of Al 2p and Gd 4d core levels, complemented by transmission electron microscopy, further suggest that the dielectric layer was segregated. Valence band measurements confirm the effective passivation of InP, indicating unpinning of the surface Fermi level.
The atomic layer deposition of titanium oxide TiO2 on ruthenium and oxidized ruthenium with titanium methoxide as metal precursor
and H2O and O3 as oxidant was investigated by Rutherford backscattering (RBS) and time of flight secondary ion mass spectrometry (TOFSIMS). An ultra-thin layer of TiO2 deposited a priori with H2O plays the role of protection of Ru(Ox) substrates against etching by O3. Information about thin films (∼3 nm) interfacial reactions, thickness and structure was brought by Medium Energy Ion
Scattering Spectroscopy (MEIS) and X-ray absorption spectroscopy (XAS) measurements. The growth enhancements observed in
the first stages of the deposition depends on the pre-treatment (pre-oxidation, H2O based interlayer thickness) of the Ru substrate.
Thick films (∼14 nm) were analyzed by transmission electron microscopy (TEM) and X-ray diffraction (XRD). The as deposited TiO2 films are crystalline with rutile structure, as resulted from structural analyzes. However, the presence of small amounts of anatase was detected by soft X-ray absorption spectroscopy (XAS) and is strongly influenced by the surface pre-treatment of the Ru substrate. The electrical properties (equivalent oxide thickness and leakage current density) correlate with a different rutile/anatase
ratio present in the films.