Pure and Nb-doped TiO1.5 films grown by pulsed-laser deposition for transparent p–n homojunctions

Pure and Nb-doped titanium oxide thin films were grown on sapphire substrates by pulsed-laser deposition in vacuum (10−7 mbar). The PLD growth leads to titanium oxide thin films displaying a high oxygen deficiency (TiO1.5) compared with the stoichiometric TiO2 compound. The structural and electrical properties (phase, crystalline orientation, nature and concentration of charge carriers, etc.) of these titanium oxide films were studied by XRD measurements and Hall effect experiments, respectively. The undoped TiO1.5 phase displayed a p-type semiconductivity. Doping this titanium oxide phase with Nb5+ leads to an n-type behaviour as is generally observed for titanium oxide films with oxygen deficiency (TiOx with 1.7 < x < 2). Multilayer homojunctions were obtained by the stacking of TiO1.5 (p-type) and Nb-TiO1.5 (n-type) thin films deposited onto sapphire substrates. Each layer is 75 nm thick and the resulting heterostructure shows a good transparency in the visible range. Finally, the I–V curves obtained for such systems exhibit a rectifying response and demonstrate that it is possible to fabricate p–n homojunctions based only on transparent conductive oxide thin films and on a single chemical compound (TiOx).