Epitaxial YbN thin films grown by nitrogen plasma-assisted molecular beam epitaxy

SrO films were grown on LaAlO3 substrates by molecular beam epitaxy and characterized using reflection high-energy electron diffraction (RHEED) and x-ray diffraction (XRD). The evolution of the RHEED pattern is discussed as a function of film thickness. 500Å thick SrO films were relaxed and exhibited RHEED patterns indicative of an atomically smooth surface having uniform terrace heights. Films had the epitaxial relationship (001)SrO‖(001)LaAlO3; [010]SrO‖[110]LaAlO3. This 45° in-plane rotation minimizes mismatch and leads to films of high crystalline quality, as verified by Kikuchi lines in the RHEED patterns and narrow rocking curves of the (002) XRD peak.

Growth and characterization of highly nitrogen doped ZnTe films on GaAs (001) by molecular beam epitaxy

Study of epitaxial SrTiO 3 (STO) thin films grown on Si(0 0 1)–2 × 1 substrates by molecular beam epitaxy

Bi2Sr2CuOx(2201) thin films with (011) vicinal surfaces have been prepared by molecular beam epitaxy (MBE) on vicinal LaSrGaO4(110) substrates with tilt angles of 4° and 6° toward [001]. Reflection high-energy electron diffraction (RHEED) and X-ray diffraction (XRD) patterns have indicated that the films have two kinds of domains. The epitaxial relationship between these domains and LaSrGaO4 substrates has been investigated and found that the b-axis of each domain was misoriented approximately ±12° from [110] LaSrGaO4 and the a-axis aligned along [11̄0] LaSrGaO4. The growth of the +12°-misoriented domains was achieved on 6°-tilted LaSrGaO4(110) at 690°C.

MBE growth and RHEED characterization of MnSe/ZnSe superlattices on GaAs (1 0 0) substrates

NiO is a typical material for new p-type oxide semiconductors. Conductivity of NiO can be raised with Li+ doping. In case of Li-heavy doping, we can obtain LixNiO2(0.5< × <1.0). Recently the importance of LiNiO2 has been increased as an electrode material for rechargeable lithium cells.In this work, we tried to fabricate a novel NiO material with Li+-heavily doped by applying the pulsed laser-induced room temperature (R.T.) film process. Previously, we have succeeded in the epitaxial growth of various oxide thin films at R.T. such as Sn-doped In2O3 transparent electrodes [1]. Although the many studies have been made on the deposition of NiO epitaxial thin film at low temperatures [2], there are few reports on fabrication and the conductive characteristic for Li-heavily doped NiO epitaxial films. The film deposition at R.T., which is the unequilibrium vapor phase process, is expected to result in different crystal structure and characteristics from the films grown at high-temperatures.A composition-adjusted thin film of LixNi1-xO(0.10< × <0.40) was deposited on a sapphire (α-Al2O3)(0001) or MgO(100) substrates by pulsed laser deposition (PLD) technique in 10−6 Torr of oxygen at R.T. and the high temperatures of 350 and 515°C. Crystalline properties of thin films deposited at R.T. or high temperatures were examined using reflection high energy electron diffraction (RHEED) and X-ray diffraction. For the Li-heavily doped NiO films(x>0.30) grown at R.T., a clear streak RHEED pattern showing epitaxial growth was observed. But the Li-heavily doped NiO films grown at high temperatures, exhibited the ring RHEED pattern, which indicates the policrystal growth of films. Electric conductivity of various Li-doped NiO thin films deposited at R.T. or high temperatures on sapphire (0001) substrates were measured by two-probe method. The interesting results were obtained that conductivity of the film was increased remarkably with an increase of Li-doping for R.T. deposition, but was not changed so much regardless of Li-doping for high-temperature depositions.

Molecular beam epitaxy growth of [CrGe/MnGe/FeGe] superlattices: Toward artificial B20 skyrmion materials with tunable interactions

SnS2 and SnSe2 thin films were deposited by molecular beam epitaxy (MBE) methods on a variety of layered semiconductor substrates (freshly cleaved SnS2, SnSe2, WSe2, MoS2, MoTe2, GaSe, InSe) and cleaved mica, for investigation of the interfaces formed as a result of MBE growth. These ultrathin films were characterized in situ by x-ray photoelectron spectroscopy and surface reflection high energy and low energy electron diffraction techniques. The growth modes were verified ex situ by scanning tunneling microscopy and/or atomic force microscopy [scanning probe microscopies (SPM)]. Despite the chemical and structural similarities between SnS2 and SnSe2, SPM measurements show that the two materials as ultrathin films have different growth morphologies in the first few monolayers. Photoelectron spectroscopy (PES) measurements lead to the conclusion that both materials grow on the basal planes of most layered substrates in an epitaxial, layer-by-layer mode. Small deviations from ideal Frank–van der Merwe growth for these thin films could be determined from PES intensity ratios versus coverage. Deposition of both materials on freshly cleaved mica, where the lattice mismatch between the substrate and the overlayer surface unit cell dimension exceeds 40%, yields exclusively 500–1000 Å diameter epitaxial islands with threefold symmetry.

Thin film perovskite-type oxide SrTiO3 has been grown epitaxially on Si(001) substrate by molecular beam epitaxy. Reflection high energy electron diffraction and x-ray diffraction analysis indicate high quality SrTiO3 heteroepitaxy on Si substrate with SrTiO3(001)//Si(001) and SrTiO3[010]//Si[110]. The SrTiO3 surface is atomically as smooth as the starting substrate surface, with a root mean square roughness of 1.2 Å observed by atomic force microscopy. The thickness of the amorphous interfacial layer between SrTiO3 and Si has been engineered to minimize the device short channel effect. An effective oxide thickness <10 Å has been obtained for a 110 Å thick dielectric film. The interface state density between SrTiO3 and Si is 6.4×1010 cm−2 eV−1, and the inversion layer carrier mobilities are 221 and 62 cm2 V−1 s−1 for n- and p-channel metal–oxide–semiconductor devices with 1.2 μm effective channel length, respectively. The gate leakage in these devices is two orders of magnitude smaller than a comparable SiO2 gate dielectric metal–oxide–semiconductor field effect transistors.

The exploration initiated by the discovery of the topological insulator (BixSb1-x)2Te3 has extended to unlock the potential of quantum anomalous Hall effects (QAHEs), marking a revolutionary era for topological quantum devices, low-power electronics, and spintronic applications. In this study, we present the epitaxial growth of Cr-doped (Bi0.4Sb0.6)2Te3 (Cr:BST) thin films via molecular beam epitaxy, incorporating various Cr doping concentrations with varying Cr/Sb ratios (0.025, 0.05, 0.075, and 0.1). High-quality crystalline of the Cr:BST thin films deposited on a c-plane sapphire substrate has been rigorously confirmed through reflection high-energy electron diffraction (RHEED), X-ray diffraction (XRD), and high-resolution transmission electron microscopy (HRTEM) analyses. The existence of a Cr dopant has been identified with a reduction in the lattice parameter of BST from 30.53 ± 0.05 to 30.06 ± 0.04 Å confirmed by X-ray diffraction, and the valence state of Cr verified by X-ray photoemission (XPS) at binding energies of ~573.1 and ~583.5 eV. Additionally, the influence of Cr doping on lattice vibration was qualitatively examined by Raman spectroscopy, revealing a blue shift in peaks with increased Cr concentration. Surface characteristics, crucial for the functionality of topological insulators, were explored via Atomic Force Microscopy (AFM), illustrating a sevenfold reduction in surface roughness as the Cr concentration increased from 0 to 0.1. The ferromagnetic properties of Cr:BST were examined by a superconducting quantum interference device (SQUID) with a magnetic field applied in out-of-plane and in-plane directions. The Cr:BST samples exhibited a Curie temperature (Tc) above 50 K, accompanied by increased magnetization and coercivity with increasing Cr doping levels. The introduction of the Cr dopant induces a transition from n-type ((Bi0.4Sb0.6)2Te3) to p-type (Cr:(Bi0.4Sb0.6)2Te3) carriers, demonstrating a remarkable suppression of carrier density up to one order of magnitude, concurrently enhancing carrier mobility up to a factor of 5. This pivotal outcome is poised to significantly influence the development of QAHE studies and spintronic applications.

A combination of the surface diagnostic techniques Auger electron spectroscopy (AES), reflection high energy electron diffraction (RHEED), and secondary ion mass spectroscopy (SIMS) was used in order to get more detailed information on basic processes which lead to the formation of high quality monocrystalline GaAs and Al x Ga1−x As films by molecular beam epitaxy (MBE) under ultra-high vacuum conditions. The formation and changes of reconstructed surface structures on (100) GaAs as a function of growth parameters were observedduring growth by RHEED. AES was used to determine the relative ratio of Ga/As on the surface for different reconstructed structures, to investigate the impurity contamination on substrate surfaces and grown films, and to study the surface segregation of Sn in MBE GaAs during doping. Finally, intentional and unintentional impurities incorporated during the growth of GaAs and Al x Ga1−x As by MBE were detected by the SIMS technique immediately after growth within the reaction chamber.

A tri-buffer method was applied to achieve layer-by-layer growth of high-quality ZnO films on sapphire (0001) substrates by rf plasma-assisted molecular beam epitaxy (MBE). After sufficient nitridation of the substrate, MgO and ZnO buffer layers were subsequently deposited on the resulting AlN layer. An atomically smooth ZnO surface with a roughness less than 1 nm in a 10 μm × 10 μm scanned area was obtained with this method. The crystal quality was also improved, as characterized by reflection high-energy electron diffraction (RHEED), x-ray diffraction (XRD), Raman spectroscopy, and transmission electron microscopy (TEM). The results indicate that the tri-buffer process could reduce the large lattice mismatch between ZnO and nitrided sapphire and facilitate the two-dimensional (2-D) growth of the ZnO epilayer. A model is proposed to understand the observations.

Molecular beam epitaxy and field emission deposition for metal film growth on III–V compound semiconductors—A comparative study

The effect of Sr deposition on the chemically formed SiO2 layer of Si(001) substrates and consequently the growth of SrTiO3 thin films on the Si(001)-Sr(2×1) surface have been studied using reflection high-energy electron diffraction (RHEED), X-ray diffraction and atomic force microscopy. After Sr deposition on the chemically formed SiO2/Si surface, a stable and well ordered Si(001)-Sr(2×1) surface is formed. The SrTiO3 film grown on the reconstructed Si(001)-Sr(2×1) surface at 350°C is amorphous. The sharp, streaky RHEED patterns and the strong STO (002) diffraction peaks and the smooth surface with root mean square roughness of approximately 4 Å suggest that high-quality SrTiO3 films are fabricated at temperatures (400–500°C) using molecular oxygen in molecular beam epitaxy.

In-situ reflection high-energy electron diffraction (RHEED) observation and X-ray diffraction measurements were performed on heterojunction interfaces of CuGaSe2/CnInSe2/CuGaSe2 grown on GaAs (001) using migration-enhanced epitaxy. The streaky RHEED pattern and persistent RHEED intensity oscillations caused by the alternate deposition of migration-enhanced epitaxy sequence are observed and the growths of smooth surfaces are confirmed. RHEED observation results also confirmed constituent material interdiffusion at the heterointerface. Cross-sectional transmission electron microscopy showed a flat and abrupt heterointerface when the substrate temperature is as low as 400 °C. These have been confirmed even by X-ray diffraction and photoluminescence measurements.