Assessment through first-principles calculations of an intermediate-band photovoltaic material based on Ti-implanted silicon: Interstitial versus substitutional origin

Open Access
Publisher Website
Google Scholar
Abstract
Quantum calculations based on density-functional theory are carried out with the aim of discovering the origin of the electronic properties of Ti-implanted Si. This compound is a potential kind of intermediate-band photovoltaic material. Experimental results show a donor level at a few tenths of an eV below the conduction band for this compound. This could correspond to the electronic transition from an intermediate band to the conduction band of the host silicon. The structural, energetic, and electronic properties of several possible configurations appearing from the implantation of Ti on Si are calculated at different dilution levels in order to agree with the experimental conditions. Among the implantation processes, all of which are energetically unfavorable, interstitial Ti setting implies the energetic balance closest to the equilibrium, which agrees with the experimental measurements. Our conclusions predict that interstitial Ti atoms are responsible for the electronic transition found from the measurements, forecasting that a band fulfilling all the requirements of an intermediate-band material is formed in the compound. The optical absorption coefficient of an interstitially Ti-implanted Si compound is shown to illustrate the photoabsorption enhancement achieved in the main part of the solar spectrum with regard to bulk Si.