Fabrication and characterization of Schottky barrier diodes on rutile TiO 2

Journal of Applied Physics

et al. 2020

Self Cite

We have used a combination of optical absorption and electrical conductivity measurements to study the effect of the main donor on small polarons in rutile TiO 2 single crystals rendered n-type conductive by hydrogenation or doping with Nb. The electrical conductivity measured at 295 K for hydrogenated samples shows a clear correlation with the interstitial hydrogen (H i ) concentration, which is consistent with reports that H i is the main shallow donor in rutile TiO 2 . Conductive samples exhibit two distinct optical absorption bands in the IR spectral region, at ω 1 = 6500 cm −1 (∼0.8 eV) and ω 2 = 3100 cm −1 (∼0.4 eV), which are present in both hydrogen-rich and Nb-doped samples. The intensities of the absorption bands are proportional to the electrical conductivity, and they exhibit an Arrhenius-like temperature dependence for temperatures between 25-50 K and 50-100 K for H-doped and Nb-doped samples, respectively. The thermal activation energies (E A s) for the absorption bands depend strongly on the main donor: ω 2 exhibits E A (H) and E A (Nb) of ∼4 and ∼10 meV, respectively, whereas ω 1 shows E A (H) and E A (Nb) of ∼1 and ∼2 meV, respectively. The combination of temperature-dependent data for the optical absorption bands and interstitial deuterium (D i )-small polaron vibrational lines support a model where the thermal activation is associated with the reconfiguration of small polarons involving Ti sites far away from the donor. The thermal activation of the optical absorption bands gives us insight into the dynamics of donor-dependent small polaron reconfiguration in rutile TiO 2 .

Section: Experimental Methodssupporting

confidence: 79%

Donors and polaronic absorption in rutile TiO2 single crystals

Weiser

Journal of Applied Physics

et al. 2020

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“…A back side contact was made by depositing a stack of Ti/Al layers over the whole back side surface of the wafer: (1) a 10-nm Ti-layer on TiO 2 and (2) a 150-nm Al-layer on Ti. This resulted in Schottky diodes with a rectification of up to eight orders of magnitude 18 . After initial electrical measurements, the samples were implanted at room temperature with 200-keV H + ions to different doses in the range 6 × 10 12 —3 × 10 14 cm −2 .…”

Section: Methodsmentioning

confidence: 99%

On the permittivity of titanium dioxide

Weiser

et al. 2021

Sci Rep

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Conductive rutile TiO2 has received considerable attention recently due to multiple applications. However, the permittivity in conductive, reduced or doped TiO2 appears to cause controversy with reported values in the range 100–10,000. In this work, we propose a method for measurements of the permittivity in conductive, n-type TiO2 that involves: (i) hydrogen ion-implantation to form a donor concentration peak at a known depth, and (ii) capacitance–voltage measurements for donor profiling. We cannot confirm the claims stating an extremely high permittivity of single crystalline TiO2. On the contrary, the permittivity of conductive, reduced single crystalline TiO2 is similar to that of insulating TiO2 established previously, with a Curie–Weiss type temperature dependence and the values in the range 160–240 along with the c-axis.

“…Conductive n-type Pd contacts with a diameter of around 400 μm were deposited through a shadow mask, resulting in Schottky barrier diodes with a rectification of up to eight orders of magnitude [ 17 ]. After initial electrical measurements, the samples were implanted at room temperature with 200-keV H + ions to different doses in the range 6×10 12 -3×10 14 cm −2 .…”

Section: A Samplesmentioning

confidence: 99%

“…Conductive n-type TiO2 samples of bluish colour were obtained by heat treatments in forming gas (FG) flow (N2 + H2 with [H2]/[N2] ≈ 1/9) at 600 • C for 90 min (hydrogenating and reducing heat treatment) or in N2 flow at 1100 • C for 60 min (reducing heat treatment). After the heat treatments, circular 150-nm thick Pd contacts with a diameter of around 400 μm were deposited through a shadow mask, resulting in Schottky barrier diodes with a rectification of up to eight orders of magnitude [ 17 ]. After initial electrical measurements, the samples were implanted at room temperature with 200-keV H + ions to different doses in the range 6×10 12 -3×10 14 cm −2 .…”

Section: A Samplesmentioning

confidence: 99%

On the dielectric constant of titanium dioxide

et al. 2021

Preprint

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Conductive rutile TiO2 has received considerable attention recently due to a number of applications. However, the static dielectric constant in conductive, reduced or doped TiO2 appears to cause controversy with reported values in the range 100-10000. In this work, we propose a method for measurements of the dielectric constant in conductive, n-type TiO2 that involves: (i) hydrogen implantation to form a donor profile at a known depth, and (ii) capacitance-voltage measurements for donor profiling. We can not confirm the claims stating an extremely high dielectric constant. On the contrary, the dielectric constant of conductive, reduced rutile TiO2 is similar to that of insulating rutile TiO2 established previously, with a Curie-Weiss type temperature dependence and the values in the range 160-240 along the c-axis.