ZnGeN2 films were grown on GaN-on-sapphire templates via metalorganic chemical vapor deposition. Energy dispersive x-ray spectroscopy was used to estimate the Zn/(Zn + Ge) composition ratio in the films. This ratio decreased with an increase in growth temperature but increased with an increase in total reactor pressure or the Zn/Ge precursor flow rate ratio. Systematic mapping of these key growth parameters has allowed us to identify the growth window to achieve ZnGeN2 with stoichiometric cation composition. Compositional and statistical analyses performed on data acquired from atom probe tomography provided insight into the local compositional homogeneity. The cations Zn and Ge did not demonstrate segregation or clustering at the sub-nanometer level. Based on x-ray diffraction 2θ–ω scan profiles and transmission electron microscope nano-diffraction patterns, the films with near-stoichiometric cation ratios were single crystalline with planar surfaces, whereas zinc-rich or zinc-poor films were polycrystalline with nonplanar surfaces. The growth direction of the single crystalline ZnGeN2 films on GaN templates was along the c-axis. Room temperature Raman spectra showed features associated with the phonon density of states, indicating the presence of cation disorder in the lattice. A cathodoluminescence peak associated with transitions involving deep level defects was observed around 640 nm. The intensity of this peak increased by almost 2.5 times as the temperature was reduced to 77 K from room temperature. A similar peak was observed in the photoluminescence spectra collected at 80 K.

Fe 2 O 3 , VO 2 ) and perovskite oxides (e.g., SrTiO 3 , BaTiO 3 , SrZrO 3 ) have been widely explored for RS and related applications. [5][6][7][8] Significant improvements have been made in memristor technology by realizing large on/off ratio, fast switching, excellent retention, low read/ write voltage, and integration with complementary metal-oxide semiconductor technology. [5,[9][10][11] In general, there are two types of memristive switching devices: filamenttype (FT) and interface-type (IT). Most of nanoionic memristors can be categorized as FT memristors and they use the migration of defects such as oxygen vacancy) and active metal electrode ions, such as Ag + . The operation of FT memristors relies on the formation of random filaments, which induces large cycle-tocycle, cell-to-cell, and device-to-device variations. [12][13][14] The underlying switching mechanisms in FT memristors have been well studied. In addition to the roles of ionic migration on the switching, [15,16] environmental effects such as role of ambient gases have also been extensively studied. [17] It was reported that ambient oxygen or water vapor partial pressure has a profound influence on the RS behavior in different FT memristors using SiO 2 , [18] Ta 2 O 5 , [19] TiO 2 , [20] HfO 2 , [19] and SrTiO 3 [21] as a switching Interface-type (IT) resistive switching (RS) memories are promising for next generation memory and computing technologies owing to the filament-free switching, high on/off ratio, low power consumption, and low spatial variability. Although the switching mechanisms of memristors have been widely studied in filament-type devices, they are largely unknown in IT memristors. In this work, using the simple Au/Nb:SrTiO 3 (Nb:STO) as a model Schottky system, it is identified that protons from moisture are key element in determining the RS characteristics in IT memristors. The Au/Nb:STO devices show typical Schottky interface controlled current-voltage (I-V) curves with a large on/off ratio under ambient conditions. Surprisingly, in a controlled environment without protons/moisture, the large I-V hysteresis collapses with the disappearance of a high resistance state (HRS) and the Schottky barrier. Once the devices are re-exposed to a humid environment, the typical large I-V hysteresis can be recovered within hours as the HRS and Schottky interface are restored. The RS mechanism in Au/Nb:STO is attributed to the Schottky barrier modulation by a proton assisted electron trapping and detrapping process. This work highlights the important role of protons/moisture in the RS properties of IT memristors and provides fundamental insight for switching mechanisms in metal oxides-based memory devices.

An alloy of ZnGeN 2 and GaN in equal proportions can form the octet-rule-preserving quaternary heterovalent nitride semiconductor ZnGeGa 2 N 4 . Singlecrystal films of the alloy targeting this composition were deposited on (11̅ 02) Al 2 O 3 (r-plane sapphire), (0001) Al 2 O 3 (c-plane sapphire), and (0001) GaN/Al 2 O 3 by metal−organic chemical vapor deposition using the precursors diethylzinc, germane, trimethylgallium, and ammonia. The growth directions were along the c-axis for films grown on the cplane sapphire and GaN templates, as well as along the orthorhombic [010] axis for films grown on r-plane sapphire. The effects of varying the growth temperature from 550 to 700 °C, choice of substrate, and trimethylgallium and germane flow rates on film composition and morphology were examined by Xray diffraction, field-emission scanning electron microscopy, and atomic force microscopy. The Zn/Ge atomic ratios were observed to decrease with growth temperature but increase with trimethylgallium flow rate. Growth rates, which varied with growth temperature from approximately 1 to 3.5 μm/h, were observed to increase with growth temperature up to 670 °C, then decrease abruptly with further increase in temperature. The growth rates were similar for growth on r-and c-plane sapphire substrates at the lower growth temperatures. However, above 650 °C the growth rates on c-and r-plane sapphire differed by as much as 70%. A broad photoluminescence double peak was observed only for samples grown on r-plane sapphire at the highest growth temperature. Hall measurements show n-type carrier concentrations in the mid-10 18 /cm −3 range and mobilities of a few cm 2 /V-s for material grown on r-sapphire substrates at 670 °C and above.

In article number 2200816, Sundar Kunwar, Aiping Chen, and co‐workers demonstrate how protons/moisture‐mediated charge trapping/detrapping controls resistive switching in interface‐type memristors, which are promising for next generation memory and computing technologies owing to the filamentfree switching, high on/off ratio, low power consumption, and spatial variability.