We report the field-effect transistors using quasi-two-dimensional electron gas generated at an ultrathin (∼10 nm) AlO/TiO heterostructure interface grown via atomic layer deposition (ALD) on a SiO/Si substrate without using a single crystal substrate. The 2DEG at the AlO/TiO interface originates from oxygen vacancies generated at the surface of the TiO bottom layer during ALD of the AlO overlayer. High-density electrons (∼10 cm) are confined within a ∼2.2 nm distance from the AlO/TiO interface, resulting in a high on-current of ∼12 μA/μm. The ultrathin TiO bottom layer is easy to fully deplete, allowing an extremely low off-current, a high on/off current ratio over 10, and a low subthreshold swing of ∼100 mV/decade. Via the implementation of ALD, a mature thin-film process can facilitate mass production as well as three-dimensional integration of the devices.

Area‐selective atomic layer deposition (AS‐ALD) offers tremendous advantages in comparison with conventional top‐down patterning processes that atomic‐level selective deposition can achieve in a bottom‐up fashion on pre‐defined areas in multi‐dimensional structures. In this work, a method for exploiting substrate‐dependent selectivity of aminosilane precursors for oxides versus nitrides through chemo‐selective adsorption is reported. For this purpose, AS‐ALD of SiO2 thin films on SiO2 substrates rather than on SiN substrates are investigated. Theoretical screening using density functional theory (DFT) calculations are performed to identify Si precursors that maximize adsorption selectivity; results indicate that di(isopropylamino)silane (DIPAS) has the potential to function as a highly chemo‐selective precursor. Application of this precursor to SiN and SiO2 substrates result in inherent deposition selectivity of ≈4 nm without the aid of surface inhibitors. Furthermore, deposition selectivity is enhanced using an ALD‐etch supercycle in which an etching step inserts periodically after a certain number of ALD SiO2 cycles. Thereby, enlarged deposition selectivity greater than ≈10 nm is successfully achieved on both blanket‐ and SiO2/SiN‐patterned substrates. Finally, area‐selective SiO2 thin films over 4–5 nm are demonstrated inside 3D nanostructure. This approach for performing inherent AS‐ALD expands the potential utility of bottom‐up nanofabrication techniques for next‐generation nanoelectronic applications.

A two-dimensional electron gas (2DEG) was formed at the interface of an ultrathin Al 2 O 3 /TiO 2 heterostructure that was fabricated using atomic layer deposition (ALD) at a low temperature (<300 °C) on a thermally oxidized SiO 2 /Si substrate. A high electron density (∼10 14 cm −2 ) and mobility (∼4 cm 2 V −1 s −1 ) were achieved, which are comparable to those of the epitaxial LaAlO 3 /SrTiO 3 heterostructure. An in situ resistance measurement directly demonstrated that the resistance of the heterostructure interface dropped significantly with the injection of trimethylaluminum (TMA), indicating that oxygen vacancies were formed on the TiO 2 surface during the TMA pulse in the ALD of Al 2 O 3 films, such that they provide electron donor states to generate free electrons at the interface of the ultrathin Al 2 O 3 /TiO 2 heterostructure. The activation energy of the electron donor states to move to the Ti 3d conduction band plays an essential role in the electrical characteristics of the 2DEG. Interestingly, the donor state level can be tailored by the control of TiO 2 crystallinity, which eventually adjusts the electron density. The activation energy was decreased to less than 20 meV to generate ultrashallow donor states while improving the TiO 2 crystallinity, such that the 2D electrons become readily delocalized, even at room temperature, to create a 2DEG.

Development at the nanoscale has established diverse and complex structures with the help of a growing selection of materials to choose from. Among the major developments that has led to these creations is the atomic layer deposition (ALD) technique that allows precise linear stepwise synthesis of various nanomaterials, which is the defining feature of ALD. Recent research activities have recorded an upsurge in the synthesis and applications of metal sulfides created via this technique. This rise in research on ALD of metal sulfides has established varying methods to deposit each metal sulfide, which necessitates a review that can analyze the major and minor advancements that have been made in the field. Hence, this comprehensive review encompasses the various ALD techniques with which metal sulfides have been synthesized, followed by a thorough account of reported chemistry and parameters by which various kinds of metal and sulfide precursors react, and finally the existing, emerging, and potential applications that incorporate metal sulfide ALD.

SiO2 is one of the most important dielectric materials that is widely used in the microelectronics industry, but its growth or deposition requires high thermal budgets. Herein, we report a low-temperature thermal atomic layer deposition (ALD) process to fabricate SiO2 thin films using a novel aminodisilane precursor with a Si–Si bond, 1,2-bis­(diisopropylamino)­disilane (BDIPADS), together with ozone. To compare the film quality, ALD SiO2 films grown at various temperatures from 250 down to 50 °C were systematically investigated. Our data suggest that even without the aid of plasma-enhanced or catalyzed surface reactions, high-quality SiO2 films with relatively high growth rates, high film densities, and low impurity contents compared to conventional Si precursors can be attained through our process at a low growth temperature (∼50 °C). Chemical analyses via Auger electron spectroscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy confirm the formation of stoichiometric SiO2 films without noticeable impurity contents of nitrogen and carbon, regardless of the growth temperature. However, low-temperature growth of the SiO2 film (≤80 °C) results in a slight ingress of SiH-related moieties during the ALD processes that is not observed at temperatures over 80 °C. Density functional theory calculations show that the Si–Si bond present in the BDIPADS precursor is easier to be oxidized compared to the Si–H bonds. Through electrical characterization of the SiO2 films grown at different temperatures, we confirm only slight degradation in the dielectric constants, leakage currents, and breakdown fields with decreasing growth temperature, which may be due to the slightly decreased film density and the increased defect density of SiH-related bonds.

Metal and transition-metal dichalcogenide (TMD) hybrid systems have been attracting growing research attention because exciton–plasmon coupling is a desirable means of tuning the physical properties of TMD materials. Competing effects of metal nanostructures, such as the local electromagnetic field enhancement and luminescence quenching, affect the photoluminescence (PL) characteristics of metal/TMD nanostructures. In this study, we prepared TMD MoS2 monolayers on hexagonal arrays of Au nanodots and investigated their physical properties by micro-PL and surface photovoltage (SPV) measurements. MoS2 monolayers on bare Au nanodots exhibited higher PL intensities than those of MoS2 monolayers on 5-nm-thick Al2O3-coated Au nanodots. The Al2O3 spacer layer blocked charge transfer at the Au/MoS2 interface but allowed the transfer of mechanical strain to the MoS2 monolayers on the nanodots. The SPV mapping results revealed not only the electron-transfer behavior at the Au/MoS2 contacts but also the lateral drift of charge carriers at the MoS2 surface under light illumination, which corresponds to nonradiative relaxation processes of the photogenerated excitons.

The ultrathin and continuous ruthenium (Ru) film was deposited through an improved atomic layer deposition (ALD) process with a discrete feeding method (DFM), called DF-ALD, employing a cut-in purge step during the precursor feeding. The excess precursor molecules can be physically adsorbed onto the chemisorbed precursors on the substrate during precursor feeding, which screens the reactive sites on the surface. Using DF-ALD, surface coverage of precursors was enhanced because the cut-in purge removes the physisorbed precursors securing the reactive sites beneath them; thus, nucleation density was greatly increased. Therefore, the grain size decreased, which changed the microstructure and increased oxygen impurity concentration. However, a more metallic Ru thin film was formed due to thermodynamic stability and improved physical density. Consequently, DF-ALD enables the deposition of the ultrathin (3 nm) and continuous Ru film with a low resistivity of ∼60 μΩ cm and a high effective work function of ∼4.8 eV.

Electrocatalyst/insulator/semiconductor configurations have been considered as promising designs for efficient photoelectrochemical (PEC) water-splitting reactions. However, the roles and effects of the insulator on the PEC reactions have not been clearly understood, in particular, for the nanoelectrocatalyst integrated semiconductor. In this study, we investigated the effects and ability of insulator material and thickness in terms of the stability and performance for PEC alkaline water reduction reaction by integrating nanocrystalline NiO x electrocatalyst/insulator/p-Si photocathodes. This was clearly understood by comparing the stability and performance of amorphous TiO x and SiO2. We demonstrated that the a-TiO x with low barrier height for electron transfer relative to that for hole transfer shows the ability for selective collection of photogenerated minority charge (electron) carriers. This enables a high open circuit potential while minimizing the kinetic overpotential required for electron transfer. The a-TiO x also renders excellent passivation ability for the Si surface defects, minimizing the recombination loss. In addition to these PEC performance improvements, the ability to protect completely the Si surface against corrosive electrolyte permeating through the nanocrystalline NiO x ensures long-term stability. All these abilities were maximized by optimizing the thickness of the a-TiO x (10 nm), thereby enabling the sustainable generation of a photocurrent of 10 mA/cm2 at a high potential level of 0.3 V (vs reversible hydrogen electrode). These results present design guidelines for the insulator along with methods to determine the effects of the insulator on PEC responses.