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In general, the electronic and optical properties of oxide films can significantly benefit from highly textured crystallinity. However, oxide films grown by atomic layer deposition (ALD), a powerful technique for the synthesis of high-quality, nanoscale thin films, usually exhibit amorphous or randomly oriented polycrystalline phases. Here, we demonstrate the growth of highly textured rutile phase ALD TiO 2 films through rational substrate design. Both a - and c -axis preferentially oriented TiO 2 films are obtained by varying the lattice parameters of the initial ALD growth surface. Under optimized conditions, we find that it is possible to deposit high-quality, c -axis preferentially aligned TiO 2 films with a bulk dielectric constant approaching 185, rivaling the single crystal limit. These films display a remarkably high dielectric constant of 117 despite thin thickness of 5.2 nm. Moreover, the addition of a single doping sequence of Al 2 O 3 successfully suppresses leakage currents to levels compatible with modern dynamic random access memory cells, all the while maintaining the high bulk dielectric constant of 137. These results clearly highlight the prospect of utilizing crystal orientation engineering in ALD thin films for emerging semiconductor devices.

Ultraviolet to infrared broadband spectral detection capability is a technological challenge for sensing materials being developed for high-performance photodetection. In this work, we stacked 9 nm-thick tellurium oxide (TeO x ) and 8 nm-thick InGaSnO (IGTO) into a heterostructure at a low temperature of 150 °C. The superior photoelectric characteristics we achieved benefit from the intrinsic optical absorption range (300-1500 nm) of the hexagonal tellurium (Te) phase in the TeO x film, and photoinduced electrons are driven effectively by band alignment at the TeO x /IGTO interface under illumination. A photosensor based on our optimized heterostructure exhibited a remarkable detectivity of 1.6 × 10 13 Jones, a responsivity of 84 A/W, and a photosensitivity of 1 × 10 5 , along with an external quantum efficiency of 222% upon illumination by blue light (450 nm). Simultaneously, modest detection properties (responsivity: ∼31 A/W, detectivity: ∼6 × 10 11 Jones) for infrared irradiation at 970 nm demonstrate that this heterostructure can be employed as a broadband phototransistor. Furthermore, its low-temperature processability suggests that our proposed concept might be used to design array optoelectronic devices for wide band detection with high sensitivity, flexibility, and stability.

In this work, high-performance amorphous In 0.75 Ga 0.23 Sn 0.02 O ( a -IGTO) transistors with an atomic layer-deposited Al 2 O 3 dielectric layer were fabricated at a maximum processing temperature of 150 °C. Hydrogen (H) and excess oxygen (O i ) in the Al 2 O 3 film, which was controlled by adjusting the oxygen radical density (P O2 : flow rate of O 2 /[Ar+O 2 ]) in the radio-frequency (rf) plasma during ALD growth of Al 2 O 3 , significantly affected the performance and stability of the resulting IGTO transistors. The concentrations of H and O i in Al 2 O 3 /IGTO stacks according to P O2 were characterized by secondary ion mass spectroscopy, X-ray photoelectron spectroscopy, hard X-ray photoemission spectroscopy, and thermal desorption spectroscopy. The high concentration of H at a low P O2 of 2.5% caused heavy electron doping in the underlying IGTO during thermal annealing at 150 °C, leading to a conductive behavior in the resulting transistor without modulation capability. In contrast, a high P O2 condition of 20% introduced O 2 molecules (or O i ) into the Al 2 O 3 film, which negatively impacted the carrier mobility and caused anomalous photo-bias instability in the IGTO transistor. Through in-depth understanding of how to manipulate H and O i in Al 2 O 3 by controlling the P O2 , we fabricated high-performance IGTO transistors with a high field-effect mobility (μ FE ) of 58.8 cm 2 /Vs, subthreshold gate swing ( SS ) of 0.12 V/decade, threshold voltage ( V TH ) of 0.5 V, and I ON/OFF ratio of ∼10 9 even at the maximum processing temperature of 150 °C. Simultaneously, the optimized devices were resistant to exposure to external positive gate bias stress (PBS) and negative bias stress (NBS) for 3600 s, where the V TH shifts for exposure to PBS and NBS for this duration were 0.1 V and -0.15 V, respectively.