Improved electrical transport in lightly Er-doped sol–gel spin-coating SnO2 thin films, processed by photolithography

Abstract

Sol-gel spin-coating SnO 2 thin films were deposited and processed through positive photolithography (liftoff), avoiding surface interaction with gaseous oxygen species and leading to samples with higher stability and data reproducibility, when submitted to electrical characterization. Processing includes: (1) a narrow conduction channel, (2) the assembly of electric contacts by ultrasound soldering, (3) deposition of an insulating layer, preventing the surface contact with atmospheric oxygen, which contributes for reliable measurements and the possibility of measuring SnO 2 matrix properties without influence of adsorbed oxygen. Lightly Er-doped SnO 2 sample (0.05 at.%), processed by this manner, has allowed the observation of a maximum about 50 K, in the temperaturedependent resistivity curve, which has not been found previously. This result is probably related to the combination of free electron concentration, which grows with temperature, and the grain boundary scattering, which decreases with temperature, and is the dominant mechanism for sol-gel SnO 2 . The processing also assures a remarkable reproducibility in the decay of photo-induced conductivity, yielding reliability to apply a modeling for the determination of important decay parameters, such as capture energy and grain boundary potential barrier.

Effects of Solution History on Sol‐Gel Processed Tin‐Oxide Thin‐Film Transistors

“…Figure compares the XRD patterns from SbTO layers obtained from fresh and aged solutions. In both cases, the SbTO thin films appear to be polycrystalline, with diffraction peaks that can be assigned to a SnO 2 rutile tetragonal phase . The XRD patterns also present contributions from the underlying amorphous SiO 2 layer, due to the grazing angle at which they are recorded.…”

“…Sb situated at a grain boundary does not necessarily function as an electron donor. It may contribute to the formation of high concentration of defects, for instance, oxygen vacancies at the grain boundaries . Such defects may act as charge carrier traps that promote electron confinement, and limiting the doping effectiveness, as well as the carrier concentration and mobility.…”

“…Doped transparent oxides, including tin oxide and zinc oxide, are being extensively explored as candidate materials for active layers in TFTs for flat panel displays. Tin oxide (SnO 2 ) is an n‐type semiconductor material with large band gap (3.6 eV), high optical transparency, low resistivity, and high thermal stability, widely used in solar cells, catalysis, transparent electronics, and sensing . In an earlier study, Presley et al demonstrated the fabrication of transparent TFTs utilizing ultrathin channel layers of SnO 2 , with field‐effect mobility of the order of 0.8 and 2.0 cm 2 /V/s in enhancement and depletion mode, respectively, with active layers grown by radio‐frequency magnetron sputtering under ultrahigh vacuum.…”

Emission Properties Related to Distinct Phases of Sol-Gel Dip-Coating Titanium Dioxide, and Carrier Photo-Excitation in Different Energy Ranges

“…It has been carried out for SnO 2 thin films with several sort of doping such as Er-doped and Eu-doped 26,36 or Sb-doped SnO 2 37 . However the scope here is not to model it but only to report the effect of monochromatic light excitation and current decay, and besides, to show the much faster effect of carrier capture compared to SnO 2 .…”

“…Current decay measurements were performed in a Janis closed-He cryostat coupled to a He compressor (HC-2 model, Intermagnetic General Corp. -ODA) 26 , and a temperature controller (model 330, Lake Shore Cryotronics). Optical excitation of samples were provided with distinct light sources: deuterium lamp coupled to an interference filter with peak at 270 nm (above TiO 2 bandgap energy), and also InGaN LED with wavelength in the range 440-460nm, and central peak of 450 nm (energy below bandgap of TiO 2 anatase phase).…”