n-Type doping of SnO2 thin films by Sb ion implantation

Abstract

The effects of Sb implantation into textured thin films of SnO, prepared by RF sputtering have been characterised by a range of techniques including secondary ion mass spectrometry (SIMS), X-ray and ultraviolet photoelectron spectroscopies (XPS and UPS), infrared reflectance, X-ray diffraction and conductivity measurements. The depth distribution of implanted 12'Sb ions at low dose is characterised by a truncated bell-shaped distribution, with mean implantation ranges of 250 8, for 90 keV implantation and 370 8, for 150 keV implantation. However, owing to surface sputtering, the maximum in the implantation profile shifts toward the surface with increasing ion dose and for 90 keV ions at doses above 3 x 10l6 ern-,, the implantation profile is sputter limited with maximum implant concentration at the surface. Electrical activation of the implanted ions is achieved at temperatures lower than those required to cause complete sintering of the small grains of the as-deposited films. The surface concentration of Sb seen in XPS increases during post-annealing treatments for Sb doses up to 3 x 1015 ern-,, but decreases at the higher dose of 3 x 10l6 ern-,. These observations are discussed in terms of Sb segregation and Sb, O, evaporation during the post-annealing treatment. The effects of Sb in introducing carriers into the surface region are investigated both by conductivity measurements and by UPS. The latter technique reveals directly occupation of Sn 5s conduction band states. Sb-implanted SnO, thin films can be used as sensors for detection of methane at much lower temperatures than is possible with undoped films.

Study of Surface Segregation of Antimony on SnO2 Surfaces by Computer Simulation Techniques

“…However, when the attachment energies are considered, we find the two planes (110 and 001) are very close in energy, which is in accordance with experimental observations, where the two planes are both observed. Note that the six faces with the lowest surface energies correspond exactly to those observed by experiment. − To the authors knowledge, the remainder of the surfaces have yet to be observed; thus, our calculations explain the experimental observations in terms of both thermodynamic and kinetic stability, in contrast to previous atomistic studies. , …”

“…Note that the six faces with the lowest surface energies correspond exactly to those observed by experiment. [29][30][31][32][33][34] To the authors knowledge, the remainder of the surfaces have yet to be observed; thus, our calculations explain the experimental observations in terms of both thermodynamic and kinetic stability, in contrast to previous atomistic studies. 14,15 B. Segregation Energies.…”

Deep vs shallow nature of oxygen vacancies and consequentn-type carrier concentrations in transparent conducting oxides

“…SnO 2 is easily n-dopable [70,71], but undoped samples only gain significant carrier concentrations at elevated temperatures [33][34][35] (although Fonstad et al [72] have shown concentrations of ∼10 17 cm −3 at room temperature). A clear increase in conductivity as P O 2 is decreased can be observed when temperature T > 1000 K, indicating the presence of a relatively deep donor [34].…”

Thermodynamic calculations of stannic oxide surfaces

“…The shell model of Freeman and Catlow [6] was used. Experiments on thin films ( [7]) support this conclusion; the (001) texture disappears on annealing.…”