Thin films of hafnium oxide have been grown by high pressure reactive sputtering on transparent quartz substrates (UV-grade silica) and silicon wafers. Deposition conditions were adjusted to obtain polycrystalline as well as amorphous films. Optical properties of the films deposited on the silica substrates were investigated by transmittance and reflectance spectroscopy in the ultraviolet, visible and near infrared range (UV-VIS-NIR). A numerical analysis method that takes into account the different surface roughness of the polycrystalline and amorphous films was applied to calculate the optical constants (refractive index and absorption coefficient). Amorphous films were found to have a higher refractive index and a lower transparency than polycrystalline films. This is attributed to a higher density of the amorphous samples, which was confirmed by atomic density measurements performed by heavy-ion elastic recoil detection analysis (ERDA). The absorption coefficient gave an excellent fit to the Tauc law (indirect gap), which allowed to obtain a band gap value of 5.54 eV. The structure of the films (amorphous or polycrystalline) was found to have no significant influence on the nature of the band gap. The Tauc plots also give information about the structure of the films, because the slope of the plot (the Tauc parameter) is related to the degree of order in the bond network. The amorphous samples had a larger value of the Tauc parameter, i.e., more order than the polycrystalline samples. This is indicative of a uniform bond network with percolation of the bond chains, in contrast to the randomly oriented polycrystalline grains separated by grain boundaries.2

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Ion implantation of Ti into Si at high doses has been performed. After laser annealing the maximum average of substitutional Ti atoms is about 1018 cm−3. Hall effect measurements show n-type samples with mobility values of about 400 cm2/V s at room temperature. These results clearly indicate that Ti solid solubility limit in Si has been exceeded by far without the formation of a titanium silicide layer. This is a promising result toward obtaining of an intermediate band into Si that allows the design of a new generation of high efficiency solar cell using Ti implanted Si wafers.

Oxide-semiconductor interface quality of high-pressure reactive sputtered (HPRS) TiO 2 films annealed in O 2 at temperatures ranging from 600 to 900 • C, and atomic layer deposited (ALD) TiO 2 films grown at 225 or 275 • C from TiCl 4 or Ti(OC 2 H 5 ) 4 , and annealed at 750 • C in O 2 , has been studied on silicon substrates. Our attention has been focused on the interfacial state and disordered-induced gap state densities. From our results, HPRS films annealed at 900 • C in oxygen atmosphere exhibit the best characteristics, with D it density being the lowest value measured in this work (5-6 × 10 11 cm −2 eV −1 ), and undetectable conductance transients within our experimental limits. This result can be due to two contributions: the increase of the SiO 2 film thickness and the crystallinity, since in the films annealed at 900 • C rutile is the dominant crystalline phase, as revealed by transmission electron microscopy and infrared spectroscopy. In the case of annealing in the range of 600-800 • C, anatase and rutile phases coexist. Disorder-induced gap state (DIGS) density is greater for 700 • C annealed HPRS films than for 750 • C annealed ALD TiO 2 films, whereas 800 • C annealing offers DIGS density values similar to ALD cases. For ALD films, the studies clearly reveal the dependence of trap densities on the chemical route used.

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