The doping of conventional semiconductors with deep level (DL) centers has been proposed to synthesize intermediate band materials. A recent fundamental study of the nonradiative recombination (NRR) mechanisms predicts the suppression of the NRR for ultrahigh DL dilutions as a result of the delocalization of the impurity electron wave functions. Carrier lifetime measurements on Si wafers doped with Ti in the 1020–1021 cm−3 concentration range show an increase in the lifetime, in agreement with the NRR suppression predicted and contrary to the classic understanding of DL action.

We present Raman-scattering measurements on ${\mathrm{In}}_x{\mathrm{Ga}}_{1-x}\mathrm{N}$ over the entire composition range of the alloy. The frequencies of the $A_1\left(\mathrm{LO}\right)$ and $E_2$ modes are reported and show a good agreement with the one-mode behavior dispersion predicted by the modified random-element isodisplacement model. The $A_1\left(\mathrm{LO}\right)$ mode displays a high intensity relative to the $E_2$ mode due to resonant enhancement. For above band-gap excitation, the $A_1\left(\mathrm{LO}\right)$ peak displays frequency shifts as a function of the excitation energy due to selective excitation of regions with different In contents, and strong multiphonon scattering up to 3LO is observed in outgoing resonance conditions.

Ion implantation of Ti into Si at high doses has been performed. After laser annealing the maximum average of substitutional Ti atoms is about ${10}^{18}{\text{cm}}^{-3}$ . Hall effect measurements show $n$ -type samples with mobility values of about $400{\text{cm}}^2/\text{V}\text{s}$ 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.

We have analyzed the structural and optical properties of Si implanted with very high Ti doses and subsequently pulsed-laser melted (PLM). After PLM, all samples exhibit an abrupt and roughly uniform, box-shaped Ti profile, with a concentration around 2 × 10²⁰ cm⁻³, which is well above the Mott limit, within a 150 nm thick layer. Samples PLM-annealed at the highest energy density (1.8 J/cm²) exhibit good lattice reconstruction. Independent of the annealing energy density, in all of the samples we observe strong sub-bandgap absorption, with absorption coefficient values between 4 × 10³ and 10⁴ cm⁻¹. These results are explained in terms of the formation of an intermediate band (IB) originated from the Ti deep levels.

In this paper, we present a detailed characterization of high quality layers of Si implanted with Ti at high doses. These layers are intended to the formation of an intermediate band (IB) solar cell. The main requirement to obtain an IB material is to reach an impurity concentration beyond the Mott limit, which is, in this case, much higher than the solid solubility limit. To overcome this limit we used the combination of ion implantation and pulsed-laser melting as nonequilibrium techniques. Time-of-flight secondary ion mass spectrometry measurements confirm that Ti concentration exceeds the theoretical Mott limit in the implanted layer, and glancing incidence x-ray diffraction and transmission electron microscopy measurements prove that good crystallinity can be achieved. Sheet resistance and Hall effect mobility show uncommon characteristics that can only been explained assuming the IB existence.