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Amorphous oxide semiconductors (AOSs) with low off-currents and processing temperatures offer promising alternative materials for next-generation high-density memory devices. The complex vertical stacking process of memory devices significantly increases the probability of encountering internal contact issues. Conventional surface treatment methods developed for planar devices necessitate efficient approaches to eliminate contact issues at deep internal interfaces in the nanoscale complex structures of AOS devices. In this work, we report the pioneering use of palladium thin film as a high-efficiency active hydrogen transfer pathway from the outside to the internal contact interface via low-temperature postannealing in the H 2 atmosphere, and the formation of highly conductive metallic interlayer effectively solves the contact issues at the deeply buried interfaces in devices. The application of this method reduced the contact resistance of Pd electrodes/amorphous indium-gallium-zinc oxide (a-IGZO) thin-film by 2 orders of magnitude, and thereby the mobility of thin-film transistor was increased from 3.2 cm 2 V -1 s -1 to nearly 20 cm 2 V -1 s -1 , preserving an excellent bias stress stability. This technology has wide applicability for the solution of contact resistance issues in oxide semiconductor devices with complex architectures.

Blue-emitting Cs 3 Cu 2 I 5 has attracted attention owing to its near-unity PL quantum yield and applications in DUV photodetectors and scintillators. Its PL properties originate from the unique local structure around the luminescent center, the [Cu 2 I 5 ] 3- polyhedron iodocuprate anion consisting of the edge-shared CuI 3 triangle and the CuI 4 tetrahedron dimer, which is isolated by Cs + ions. We found that solid-state reactions between CsI and CuI occur near room temperature (RT) to form Cs 3 Cu 2 I 5 and/or CsCu 2 I 3 phases. High-quality thin films of these phases were obtained by the sequential deposition of CuI and CsI by thermal evaporation. We elucidated that the formation of interstitial Cu + and the antisite of I - at the Cs + site in the CsI crystal through Cu + and I - diffusion results in the RT synthesis of Cs 3 Cu 2 I 5 . The unique structure formation of the luminescent center was revealed using a model based on the low packing density of the CsCl-type crystal structure, similar sizes of Cs + and I - ions, and the high diffusivity of Cu + . The self-aligned patterning of the luminous regions on thin films was demonstrated.

Copper iodide (CuI) is a promising p-type transparent semiconductor with excellent carrier mobility. However, the high hole concentration in conventionally fabricated CuI including the single crystal hinders its applicability to the channel layer of thin-film transistors. We found that Zn substitution into Cu + sites can effectively reduce the hole concentration. Experimental and computational examinations showed that the dominant mechanism involved the formation of a defect pair, the Zn-substituted Cu site (Zn Cu ) and Cu vacancy (V Cu ), and the simultaneous suppression of V Cu arising from the stabilization of Cu + in the Zn-substituted CuI lattice, rather than hole compensation by the electrons generated from Zn 2+ substitution into Cu + sites. Our results show that the hole concentration of Zn-substituted CuI is tunable in the range of 10 14 -10 18 cm -3 , making it suitable for thin-film transistors and hole transport layers in OLEDs.

Metal halide perovskites (MHPs) are plausible candidates for practical p-type semiconductors. However, in thin film transistor (TFT) applications, both 2D PEA 2 SnI 4 and 3D FASnI 3 MHPs have different drawbacks. In 2D MHP, the TFT mobility is seriously reduced by grain-boundary issues, whereas 3D MHP has an uncontrollably high hole density, which results in quite a large threshold voltage (V th ). To overcome these problems, a new concept based on a 2D-3D core-shell structure is herein proposed. In the proposed structure, a 3D MHP core is fully isolated by a 2D MHP, providing two desirable effects as follows. (i) V th can be independently controlled by the 2D component, and (ii) the grain-boundary resistance is significantly improved by the 2D/3D interface. Moreover, SnF 2 additives are used, and they facilitate the formation of the 2D/3D core-shell structure. Consequently, a high-performance p-type Sn-based MHP TFT with a field-effect mobility of ≈25 cm 2 V -1 s -1 is obtained. The voltage gain of a complementary metal oxide semiconductor (CMOS) inverter comprising an n-channel InGaZnO x TFT and a p-channel Sn-MHP TFT is ≈200 V/V at V DD = 20 V. Overall, the proposed 2D/3D core-shell structure is expected to provide a new route for obtaining high-performance MHP TFTs., (© 2021 The Authors. Advanced Science published by Wiley-VCH GmbH.)

The ternary nitride CaZn 2 N 2 , composed only of earth-abundant elements, is a novel semiconductor with a band gap of ∼1.8 eV. First-principles calculations predict that continuous Mg substitution at the Zn site will change the optical band gap in a wide range from ∼3.3-1.9 eV for Ca(Mg 1- x Zn x ) 2 N 2 ( x = 0-1). In this study, we demonstrate that a solid-state reaction at ambient pressure and a high-pressure synthesis at 5 GPa produce x = 0 and 0.12 and 0.12 < x ≤ 1 polycrystalline samples, respectively. It is experimentally confirmed that the optical band gap can be continuously tuned from ∼3.2 to ∼1.8 eV, a range very close to that predicted by theory. Band to band photoluminescence is observed at room temperature in the ultraviolet-red region depending on x . A 2% Na doping at the Ca site of Ca(Mg 1- x Zn x ) 2 N 2 converts its highly resistive state to a p-type conducting state. Particularly, the x = 0.50 sample exhibits intense green emission with a peak at 2.45 eV (506 nm) without any other emission from deep-level defects. These features meet the demands of III-V group nitride and arsenide/phosphide light-emitting semiconductors.