Hong-Liang Lu

Characterization of atomic-layer-deposited Al2O3∕GaAs interface improved by NH3 plasma pretreatment

Al2O3 thin films were deposited by atomic layer deposition on HF-cleaned and NH3 plasma-treated GaAs surfaces, respectively. The precursors used for Al2O3 films are trimethylaluminum and water. Effects of NH3 plasma pretreatment on the electrical and structural properties of Al2O3∕GaAs interface were investigated by C-V measurements, high-resolution transmission electron microscopy, and x-ray photoelectron spectroscopy measurements. The C-V measurements showed that the electrical property is improved after NH3 plasma pretreatment. X-ray photo electron spectroscopy analyses confirmed that GaAs oxides and elemental As are greatly decreased and the GaAs surface can be efficiently protected during NH3 plasma pretreatment and atomic layer deposition of Al2O3.

The mechanism of the asymmetric SET and RESET speed of graphene oxide based flexible resistive switching memories

Oxygen migration is reported as key factors of resistive switching in graphene oxide (GO) based memories by different groups. A flexible nonvolatile resistive switching memory based on GO was fabricated through a spin-coating process. The speed of the SET and RESET operations of the GO memories was found to be significant asymmetric. The RESET speed is in the order of 100 ns under a −5 V voltage while the SET speed is three orders of magnitude slower (100 μs) under a 5 V bias. The behavior of resistive switching speed difference is elucidated by voltage modulated oxygen diffusion barrier change.

Spectroscopic ellipsometry study of thin NiO films grown on Si (100) by atomic layer deposition

Thin NiO films are grown at 300 ° C on Si (100) using atomic layer deposition. The dependence of annealing temperature on the optical properties of NiO films has been investigated using spectroscopic ellipsometry in the spectral region of 1.24 – 5.05 eV . It is found that the refractive index and thickness of NiO films are affected by high temperature annealing. The optical band gap of the as-deposited thin NiO film is determined to be 3.8 eV , which is almost independent of the annealing temperature. The indirect band gap of NiO film shifts toward lower photon energy with an increase in annealing temperature.

Band alignment and interfacial structure of ZnO/Si heterojunction with Al2O3 and HfO2 as interlayers

Energy band alignment of ZnO/Si heterojunction with thin interlayers Al2O3 and HfO2 grown by atomic layer deposition has been studied using x-ray photoelectron spectroscopy. The valence band offsets of ZnO/Al2O3 and ZnO/HfO2 heterojunctions have been determined to be 0.43 and 0.22 eV, respectively. Accordingly, the band alignment ZnO/Si heterojunction is then modified to be 0.34 and 0.50 eV through inserting a thin Al2O3 and HfO2 layer, respectively. The feasibility to tune the band structure of ZnO/Si heterojunction by selecting a proper interlayer shows great advantage in improving the performance of the ZnO-based optoelectronic devices.

Enhancement of Resistive Switching Characteristics in

Resistive switching behaviors of Al2O3-based memory devices with and without ruthenium nanocrystals (RuNCs) fabricated by atomic layer deposition are investigated for nonvolatile-memory applications. Large resistance ratios (>; 105) of high- to low-resistance states were observed with nanocrystals contribution. Moreover, improvements of stability device yield and retention performance were also achieved by embedding RuNCs. Therefore, the Al2O3-based resistive memory device composed of embedded nanocrystals is a possible solution for future integrated standalone storage class memory processes.

\hbox{Al}_{2}\hbox{O}_{3}

NiO films were grown on Si(100) by atomic layer deposition using Ni(Cp) 2 (Cp = cyclopentadienyl, C 5 H 5 ) or Ni(EtCp) 2 [EtCp = ethylcyclopentadienyl, (C 2 H 5 ) C 5 H 4 )] and ozone in the 150-300°C temperature range. The growth temperature dependence of structure, electronic density, and impurity levels for the prepared NiO films was studied using X-ray reflectivity, X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, time of flight-secondary ion mass spectroscopy (ToF-SIMS), and transmission electron microscopy. The behavior of films deposited using Ni(Cp) 2 and Ni(EtCp) 2 is compared and discussed. NiO films with good stoichiometry and low amounts of contaminants are obtained at a growth temperature (T g ) of 250°C or above. At a fixed T g , the growth rate for NiO films deposited using Ni(Cp) 2 is higher than the one of films deposited using Ni(EtCp) 2 . Furthermore, the growth rate for NiO deposited using Ni(Cp) 2 at T g = 150°C is 0.32 nm/cycle and decreases substantially in films deposited at higher temperatures. The electronic density of NiO films deposited at 300°C is close to the one of bulk NiO (1.83 e - /A 3 ). According to XRD and FTIR results, films deposited at T g ≥ 200°C have a simple cubic polycrystalline structure. Impurities in NiO films decrease with increasing T g , as detected by ToF-SIMS.

-Based RRAM With Embedded Ruthenium Nanocrystals

Pt nanodots have been grown on Al2O3 film via atomic layer deposition (ALD) using (MeCp)Pt(Me)3 and O2 precursors. Influence of the substrate temperature, pulse time of (MeCp)Pt(Me)3, and deposition cycles on ALD Pt has been studied comprehensively by scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. Therefore, Pt nanodots with a high density of approximately 2 × 1012 cm-2 have been achieved under optimized conditions: 300°C substrate temperature, 1 s pulse time of (MeCp)Pt(Me)3, and 70 deposition cycles. Further, metal-oxide-semiconductor capacitors with Pt nanodots embedded in ALD Al2O3 dielectric have been fabricated and characterized electrically, indicating noticeable electron trapping capacity, efficient programmable and erasable characteristics, and good charge retention.

Atomic Layer Deposition of NiO Films on Si(100) Using Cyclopentadienyl-Type Compounds and Ozone as Precursors

Interfacial layer (IL) suppression is a big concern in atomic layer deposition (ALD) of high-k gate dielectrics. We have studied two kinds of surface pretreatments for ALD Al2O3 deposition: surface Al(CH3)3 (TMA) pretreatment (ST) and surface nitridation (SN). High resolution transmission electron microscopy images show that the IL has been effectively suppressed after performing surface pretreatments. X-ray photoelectron spectroscopy results indicate that both surface pretreatments are beneficial for compact Al2O3 deposition, however, the sample with SN shows much better interface thermal stability. And electrical characterizations demonstrate that the capacitor with SN exhibits better interface property, lower leakage current, and smaller capacitance-voltage (C-V) hysteresis. Based on transient capacitance measurement (C-t) and C-V measurement with different gate bias sweep ranges, a “shallow level trap” model is proposed to explain well the difference of C-V hysteresis between ST and SN.

Atomic layer deposition of high-density Pt nanodots on Al2O3 film using (MeCp)Pt(Me)3 and O2 precursors for nonvolatile memory applications

ABSTRACT A new 2D material, borophene, has been grown successfully recently on single crystal Ag substrates. Three main structures have been proposed (, and striped borophene). However, the stability of three structures is still in debate. Using first principles calculations, we examine the dynamical, thermodynamical and mechanical stability of , and striped borophene. Free-standing and borophene is dynamically, thermodynamically and mechanically stable, while striped borophene is dynamically and thermodynamically unstable due to high stiffness along a direction. The origin of high stiffness and high instability in striped borophene along a direction can both be attributed to strong directional bonding. Our work shows a deep connection between stability and strength, and helps researchers to estimate accurately the mechanical performance of 2D materials. GRAPHICAL ABSTRACT IMPACT STATEMENT A benchmark for examining the relative stability of different structures of borophene is provided. Strong directional bonding in striped borophene leads to high stiffness and high brittleness.

Spectroscopic and electrical properties of atomic layer deposition Al2O3 gate dielectric on surface pretreated Si substrate

ZnO/TiO2 nanolaminates were grown on Si (100) and quartz substrates by atomic layer deposition at 200°C using diethylzinc, titanium isopropoxide, and deionized water as precursors. All prepared multilayers are nominally 50 nm thick with a varying number of alternating TiO2 and ZnO layers. Sample thickness and ellipsometric spectra were measured using a spectroscopic ellipsometer, and the parameters determined by computer simulation matched with the experimental results well. The effect of nanolaminate structure on the optical transmittance is investigated using an ultraviolet–visible-near-infrared spectrometer. The data from X-ray diffraction spectra suggest that layer growth appears to be substrate sensitive and film thickness also has an influence on the crystallization of films. High-resolution transmission electron microscopy images show clear lattice spacing of ZnO in nanolaminates, indicating that ZnO layers are polycrystalline with preferred (002) orientation while TiO2 layers are amorphous.