Photodesorption and electron trapping in n-type SnO₂thin films grown by dip-coating technique

Abstract

Thin films of undoped and Sb-doped (2 atg%) Sn02 have been prepared by sol-gel dipcoating technique on borosilicate glasses. Variation of photoconductivity excitation with wavelength and optical absorption indicate indirect bandgap transition with energy of 3.5eV. 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 U V photoexcitation (30Snm) 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.

Persistent Photoconductivity in SnO2 Thin Films Grown by Molecular Beam Epitaxy: The Dominant Roles of Water Vapor and Carrier Concentration

“…Investigations at temperatures below 200 K are rare, and this is the first study to systematically explore the effect of carrier concentration on PPC, which is surprising given that surface electron trapping is widely assumed to be responsible for the PPC of metal oxide semiconductors. 10,13,18,20,25,26 Our results are in contrast with the dominant role usually attributed to adsorbed molecular O 2 in the PPC of SnO 2 and instead indicate that water vapor is the dominant acceptor-like species involved in our high-quality SnO 2 films.…”

Photoconductivity in In2O3 nanoscale thin films: Interrelation with chemisorbed-type conductometric response towards oxygen

“…Difficulties in describing the operation mechanism have arisen first of all due to a lack of essential information about surface electronic levels responsible for surface conductivity modulation under an environment change. In many experiments related to transparent conductive metal oxides (TCO), it was shown that there is a principal contribution from adsorbed oxygen, namely through it's desorption [1][2][3][4], in the photoconductivity (PC) properties of nanoscale metal oxides. However, we have to note that all indicated experiments were carried out at or below room temperature (RT), i.e., under conditions during which TCO photoconductivity, especially in the ultra violet (UV) range, was irreversible in many cases.…”

Er rare-earth ion incorporation in sol-gel SnO2

“…Undoped SnO 2 is an n-type semiconductor since oxygen vacancies or interstitial Sn 4+ are donor sites. In the case of sol-gel films, crystallites are rather small (3-10 nm) 3 and a lot of oxygen is adsorbed at boundary layer, trapping electrons from the conduction band 4 . Then conductivity can be greatly increased by eliminating oxygen from grain boundary layer, which can be done by annealing at proper temperature and gas composition of the annealing chamber 5 .…”