Publication: Strong subbandgap photoconductivity in GaP implanted withTi
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Publication Date
2018-03
Authors
Prado Millán, Álvaro del
García Hemme, Eric
Montero, Daniel
Gonzalo,, José
Siegel,, Jan
López,, Esther
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Wiley
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Abstract
Photovoltaic solar cells based on the intermediate band (IB) concept could greatly enhance theefficiency of future devices. We have analyzed the electrical and photoconductivity propertiesof GaP supersaturated with Ti to assess its suitability for IB solar cells. GaP:Ti was obtained byion implantation followed by pulsed‐laser melting (PLM) using an ArF excimer laser. It was foundthat PLM energy densities between 0.35 and 0.55 J/cm2produced a good recovery of thecrystalline structure of GaP (both unimplanted and implanted with Ti), as evidenced by highmobility measured values (close to the reference GaP). Outside this energy density window,the PLM failed to recover the crystalline structure producing a low mobility layer that iselectrically isolated from the substrate. Spectral photoconductivity measurements wereperformed by using the van der Pauw set up. For GaP:Ti a significant enhancement of theconductivity was observed when illuminating the sample with photon energies below 2.26 eV,suggesting that this photoconductivity is related to the presence of Ti in a concentration highenough to form an IB within the GaP bandgap. The position of the IB was estimated to be around1.1 eV from the conduction band or the valence band of GaP, which would lead to maximumtheoretical efficiencies of 25% to 35% for a selective absorption coefficients scenario and higherfor an overlapping scenario
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"Authors would like to acknowledge C.A.I. de Técnicas Físicas of theUniversidad Complutense de Madrid for ion implantation, RTA andJoule and e‐beam evaporations, and the technical and human supportprovided by Facility of Analysis and Characterization of Solids andSurfaces of SAIUEx (financed by UEX, Junta de Extremadura, MICINN,FEDER, and FSE). This work was partially supported by ProjectMADRID‐PV (grant no. P2013/MAE‐2780) funded by the Comunidadde Madrid, by the Spanish MINECO (Ministerio de Economía yCompetitividad) under grants TEC 2013‐41730‐R and TEC 2015‐69916‐C2‐1‐R, and by the Universidad Complutense de Madrid(Programa de Financiación de Grupos de Investigación UCM–BancoSantander) under grant 910173‐2014. The work of D. Montero wassupported by the Spanish MINECO under contract BES‐2014‐067585. J. Solis from the Instituto de Optica is acknowledged for help-ful discussions."