Photodesorption and electron trapping in n-type SnO2 thin films grown by dip-coating technique

Thin films of undoped and Sb-doped (2 atg%) SnO2 have been prepared by sol-gel dip-coating technique on borosilicate glasses. Variation of photoconductivity excitation with wavelength and optical absorption indicate indirect bandgap transition with energy of ≅ 3.5 eV. Conductance as function of temperature indicates two levels of capture with 39 and 81 meV as activation energies, which may be related to an Sb donor and oxygen vacancy respectively. Electron trapping by these levels are practically destroyed by UV photoexcitation (305 nm) and heating in vacuum to 200°C. Gas analysis using a mass spectrometer indicates an oxygen related level, which may not be desorbed in the simpler O2 form.

Improved Conductivity Induced by Photodesorption in SnO2 Thin Films Grown by a Sol-Gel Dip Coating Technique

Thin films of undoped and Sb-doped SnO2 have been prepared by a sol-gel dip-coating technique. For the high doping level (2-3 mol% Sb) n-type degenerate conduction is expected, however, measurements of resistance as a function of temperature show that doped samples exhibit strong electron trapping, with capture levels at 39 and 81 meV. Heating in a vacuum and irradiation with UV monochromatic light (305 nm) improve the electrical characteristics, decreasing the carrier capture at low temperature. This suggests an oxygen related level, which can be eliminated by a photodesorption process. Absorption spectral dependence indicates an indirect bandgap transition with Eg ≅ 3.5 eV. Current-voltage characteristics indicate a thermionic emission mechanism through interfacial states.