High-mobility transparent conductive thin films of cerium-doped hydrogenated indium oxide

Abstract

We have developed 100-nm-thick cerium-doped hydrogenated indium oxide (ICO:H) films with a superior Hall mobility of 130-145 cm 2 V %1 s %1 . The ICO:H films deposited at 150°C by dc arc-discharge ion plating were post-annealed at 200°C. The relationship between the Hall mobility and carrier density of the polycrystalline ICO:H films shows that the carrier transport is limited by an ionized impurity scattering mechanism inside the grains. The surfaces of the ICO:H films were found to be very smooth and clear grain-boundary areas were not observed.

In2O3‐Based Transparent Conducting Oxide Films with High Electron Mobility Fabricated at Low Process Temperatures

“…Experimentally determined N and μ data have been evaluated on the basis of theoretical carrier scattering models and used to determine the doping mechanisms. The Hall mobility values agreed well with the calculated values dominated by singly charged impurities, which suggests that the free carriers were generated by singly charged donors (e.g., Me In • , H i • , H O • ) rather than by doubly charged donors (e.g., V O •• ) in In 2 O 3 :Me, In 2 O 3 :H, and In 2 O 3 :Ce,H . However, the degenerately doped TCO films exhibited higher electron mobility with constant N at lower temperatures than at higher temperatures, indicating that the μ values measured at room temperature were limited not only by the ionized impurity scattering but also by phonon scattering .…”

“…Second, solid‐phase crystallized ( spc ‐) H‐doped In 2 O 3 (In 2 O 3 :H) films exhibit μ values greater than 100 cm 2 V −1 s −1 with N values from 1 × 10 20 to 2 × 10 20 cm −3 at low process temperatures from 150 to 200 °C . The films are fabricated using a two‐step growth process, specifically, the deposition of amorphous or amorphous‐rich In 2 O 3 :H films grown at low temperatures via magnetron sputtering, RPD, or atomic layer deposition and subsequently thermally annealed at a temperature greater than 150 °C. During annealing, solid‐phase crystallization occurs and high electron mobility is achieved.…”

“…Furthermore, the effects of dopant species (Me and H) on the grain‐barrier height and resulting transport properties in polycrystalline films have also been discussed . With respect to intragrain properties, suppressed scattering from oxygen interstitials originating from the formation of the singly charged donor (e.g., Mo In ••• O i ″, W In ••• O i ″) and suppressed scattering from defects related to oxygen deficiencies originating from the introduction of metals with higher bond strength with O than In and Sn in the In 2 O 3 host material have been discussed. In In 2 O 3 :H films, ab initio calculations revealed that interstitial H (H i • ) and substitutional H (H O • ) function as singly charged donors, being energetically more favorable than an oxygen vacancy (V O •• ) .…”

“…These films are normally deposited onto heated substrates using various growth methods (e.g., magnetron sputtering, pulsed laser deposition, and ion plating with DC arc discharge, known as high-density plasma-enhanced evaporation or reactive plasma deposition (RPD)). Second, solid-phase crystallized (spc-) H-doped In 2 O 3 (In 2 O 3 :H) films exhibit μ values greater than 100 cm 2 V À1 s À1 with N values from 1 Â 10 20 to 2 Â 10 20 cm À3 at low process temperatures from 150 to 200 C. [41] The films are fabricated using a two-step growth process, specifically, the deposition of amorphous or amorphous-rich In 2 O 3 :H films grown at low temperatures via magnetron sputtering, [41] RPD, [42] or atomic layer deposition [43] and subsequently thermally annealed at a temperature greater than 150 C. During annealing, solid-phase crystallization occurs and high electron mobility is achieved. Similar properties have also been reported for CeO 2 and hydrogen co-doped In 2 O 3 films.…”

“…Similar properties have also been reported for CeO 2 and hydrogen co-doped In 2 O 3 films. [42] Notably, spc-In 2 O 3 :H films on glass substrates fabricated at low process temperatures ( 200 C) exhibited higher μ values than Medoped epitaxial films grown at high temperatures (!600 C) on single-crystalline oxide substrates. [15,44,45] The mechanisms responsible for this high electron mobility have been investigated.…”