Ion Implant Technology for Intermediate Band Solar Cells
This chapter describes the creation of an Intermediate Band (IB) on single crystal silicon substrates by means of high-dose Ti implantation and subsequent Pulsed Laser Melting (PLM). The Ti concentration over the Mott limit is confirmed by Time-of-Flight Secondary Ion Mass Spectroscopy (ToF-SIMS) measurements and the recovery of the crystallinity after annealing by means of Glancing Incidence X Ray Diffraction (GIXRD) and Transmission Electron Microscopy (TEM). Rutherford Backscattering Spectroscopy (RBS) measurements show that most of the atoms are located interstitially. Analysis of the sheet resistance and mobility measured using the van der Pauw geometry shows a temperature-dependent decoupling between the implanted layer and the substrate. This decoupling and the high laminated conductivity of the implanted layer could not be explained except if we assume that an IB has been formed in the semiconductor. A specific model for the bilayer electrical behaviour has been developed. The fitting of this model and also the simulation of the sheet resistance with the ATLAS code allow to determine that the IB energetic position is located around 0.36–0.38 eV below the conduction band. Carriers at the IB have a density very similar to the Ti concentration and behave as holes with mobilities as low as 0.4 cm2 Vs− 1.
KeywordsConduction Band Sheet Resistance Hole Mobility Hall Mobility Rutherford Backscatter Spectroscopy
Authors would like to acknowledge the Nanotechnology and Surface Analysis Services of the Universidad de Vigo C.A.C.T.I. for ToF-SIMS measurements, the Center for Microanalysis of Materials of the Universidad Autónoma de Madrid for RBS measurements, C.A.I. de Difraccin de Rayos X of the Universidad Complutense de Madrid for GIXRD measurements, C.A.I. de Microscopa de la Universidad Complutense de Madrid for TEM analysis and C.A.I. de Técnicas Físicas of the Universidad Complutense de Madrid for ion implantation experiments. This work was made possible thanks to the FPI (Grant No. BES-2005-7063) of the Spanish Ministry of Education and Science. This work was partially supported by the Projects NUMANCIA-2 (No. S2009/ENE1477) funded by the Comunidad de Madrid GENESIS-FV (No. CSD2006-00004) funded by the Spanish Consolider National Program and by U.C.M.-C.A.M. under Grant CCG07-UCM/TIC-2804.
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