RHEED Intensity Research Articles

An effective method to calculate RHEED rocking curves from nanoheteroepitaxial systems

An effective method to calculate RHEED rocking curves from nanoheteroepitaxial systems

Ni(111)表面水素位置によるRHEED強度変化

Ni(111)表面水素位置によるRHEED強度変化

RHEED intensities from two-dimensional heteroepitaxial nanoscale systems of GaN on AlN(0 0 0 1) and AlN(0 0 0 [formula omitted]) surfaces

This paper presents a version of simulation program, which facilitates the calculation of changes to the intensity of RHEED oscillations in the function of the glancing angle of incidence of the electron beam, employing various models of scattering crystal potential for heteroepitaxial structure of hexagonal GaN film nucleated on AlN(0 0 0 1) and AlN(0 0 0 1¯) surfaces, including the possible existence of various diffuse scattering models through the layer parallel to the surface. Program summaryTitle of program: RHEED_DIFF_WWProgram Files doi:http://dx.doi.org/10.17632/hn3pt6ytky.2Licensing provisions: GNU General Public License 3Programming language used: C++Journal reference of previous version: Computer Physics Communications 207 (2016) 536–538Does the new version supersede the previous version?: No. It is a supplement to the previous version.Reasons for the new version: Responding to users’ feedback we present a practical procedure of construction of simulation program, which facilitates the calculation of changes the intensity of RHEED rocking curves, employing various models of scattering crystal potential for heteroepitaxial structure of wurtzite-type GaN on AlN. The work demonstrates that the polarity of GaN/AlN heterojunctions can be investigated in real time by RHEED rocking curves measurements.Nature of problem: Aluminum nitride is a subject of intense research as a substrate material in heterojunctions for short-wavelength optoelectronics, high-power and high-frequency electronics. The lattice constants and thermal expansion coefficients of AlN and GaN are close enough to provide a low defect density in epitaxial GaN grown on the AlN substrates. Both GaN and AlN possess a wurtzite crystal structure (non-centrosymmetric), which makes it either metal or N polar along the c-axis with [0 0 0 1] or [0 0 0 1¯] direction, respectively, and which strongly influences their physical properties [1]. From the practical point of view, the distinction between these two polarities is very important for the many applications of the GaN/AlN heterostructures [2-4].Method of solution: RHEED intensities are calculated within the general framework described in Refs. [5] and [6].Summary of revisions: The presented version of the program implements an original algorithm for calculations of scattering potentials for regular all-metal-polar GaN(0001)/AlN(0001) and all-N-polar GaN(0 0 0 1¯)/AlN(0 0 0 1¯) heterostructures, and solving a time-independent Schrödinger equation for high-energy electrons.During the numerical calculations of the changes in the intensity of the specular beam in the function of the glancing angle, it was assumed that the azimuth of the incident beam direction corresponds to the one-beam condition, the electron energy equals 10 keV, the temperature of the crystal equals 300 K, glancing angle was increased from 0.5∘ to 5.0∘, and the value of αparameter = 0.1 and β= 0.5 for the MODEL3 of the scattering potential [6] (See Figs. 1 and 3).ReferencesE. S. Hellman, MRS Internet J. Nitride Semicond. Res. 3, 11 (1998).A. Onen, D. Kecik, E. Durgun, and S. Ciraci, Phys. Rev. B 95 (2017) 155435.P. Sohi, D. Martin and N. Grandjean, Semicond. Sci. Technol. 32 (2017) 075010.M. Agrawal, K. Radhakrishnan, N. Dharmarasu1, and S. S. Pramana, Jpn. J. Appl. Phys. 54 (2015) 065701-6.A. Daniluk, Comput. Phys. Commun. 207 (2016) 536-538.A. Daniluk, Comput. Phys. Commun. 185 (2014) 3001-3009.

Real-time monitoring and control of nitride growth rates by Metal Modulated Epitaxy

The standard method for growth rate determination in semiconductor thin films, by Molecular Beam Epitaxy (MBE), is through RHEED intensity oscillations prior to device layer epitaxy. High quality III-Nitride epitaxy occurs with metal-rich surfaces and under step-flow growth conditions, which do not produce RHEED oscillations. This article demonstrates the capability to monitor the growth rate of gallium nitride (GaN), at any point during film growth with high fidelity, under step-flow growth conditions. RHEED intensity vs. time measurements determine the growth rate by Metal Modulated Epitaxy (MME). Utilizing differential analysis, a factor of 2x improvement in accuracy is demonstrated, with a Standard Error less than 4%. Complementary analysis with X-Ray Diffraction and RHEED identify the Ga bilayer thickness as 2.34 ML ± 0.08 ML, representing the first time RHEED analysis has been used to characterize the thickness of the Ga bilayer on GaN.

Step flow growth of Mn5Ge3 films on Ge(111) at room temperature

The very first stages of the non-diffusive growth of Mn5Ge3 thin films on Ge(111) substrates are characterized by several techniques. Mn5Ge3 films are grown by molecular beam epitaxy using the co-deposition of Mn and Ge atoms at room temperature. XRD measurements demonstrate that the thin films are monocrystalline. The evolution of the RHEED intensity during the deposition and the AFM images show a step-flow growth mode. RHEED patterns, combined with TEM images, prove that the lattice mismatch of 3.7% is accommodated by the formation of an array of interfacial dislocations and by the presence of a residual strain in the thin films. These observations are supported by the numerical calculations of the critical nucleation volumes exhibiting very similar values, in the case of a pseudomorphic growth or in the case of an accommodation of the lattice mismatch by interfacial dislocations. Furthermore, the effect Ge/Mn stoichiometric and Mn-rich fluxes on the surface morphology is examined.

RHEED intensities from two-dimensional heteroepitaxial nanoscale systems of GaN on a 3C-SiC(111) surface

This paper presents a version of simulation program, which facilitates the calculation of changes to the intensity of RHEED oscillations in the function of the glancing angle of incidence of the electron beam, employing various models of scattering crystal potential for heteroepitaxial structure of hexagonal (0001) GaN film nucleated on a 3C-SiC surface, including the possible existence of various diffuse scattering models through the layer parallel to the surface. New version program summaryTitle of program: RHEED_DIFF_ZProgram Files doi:http://dx.doi.org/10.17632/52nxmwzkxx.1Licensing provisions: GNU General Public License 3Programming language used: C++Journal reference of previous version: Computer Physics Communications 207 (2016) 536–538Does the new version supersede the previous version?: No. It is a supplement to the previous version.Reasons for new version:Responding to users’ feedback we present a practical procedure of construction of simulation program, which facilitates the calculation of changes to the intensity of RHEED rocking curves, employing various models of scattering crystal potential for heteroepitaxial structure of hexagonal (0001) GaN film nucleated on a 3C-SiC(111) surface.Nature of problem:Growth of GaN layers on SiC is of importance for potential electronic device applications.Silicon carbide crystallizes in numerous different modifications, so-called polytypes [1]. Among them, only hexagonal structure 4H-SiC and 6H-SiC have been thoroughly investigated while the cubic 3C-SiC polytype is lagging behind in technological developments. The 3C-SiC has a Zincblende crystal structure and is characterized by an identical orientation of all bilayers in the crystal, where the atomic geometry is repeated every three bilayers along the c-axis this crystal structure (Fig. 1). For this reason, 3C-SiC has the high electron mobility and saturation velocity by reducing phonon scattering resulting from the high symmetry. The lattice mismatch between GaN(0001) and 3C-SiC(111) is about 3.3%, and is smaller than the mismatch between GaN(0001) and Si(111) [2]. Therefore progress in investigations on crystal growth of GaN on 3C-SiC is a key issue for device developments related to this heterostructure. Researchers and technologists manufacturing two-dimensional heterostructures frequently use RHEED rocking curves to control growth of samples at the atomistic level of accuracy. The fundamental scientific problem in such research is to specify both interface type and growth mechanism for subsequent layers.Method of solution:RHEED intensities are calculated within the general framework described in Refs. [2] and [3].Summary of revisions:The presented version of the program implements an original algorithm of self-consistent calculations for scattering potentials GaN(0001)/3C-SiC(111) and solving a time-independent Schrödinger equation for high-energy electrons.During the numerical calculations of the changes in the intensity of the specular beam in the function of the glancing angle, it was assumed that the azimuth of the incident beam direction corresponds to the one-beam condition, the electron energy equals 10 keV, the glancing angle was increased from 0.5∘ to 6.5∘, and the value of αparameter=0.1 and β=0.5 for the MODEL3 of the scattering potential [3] with the model of ideal SiC/GaN interface [4].

25aB10 GaAsのMBE成長におけるリエントラントなRHEED振動の機構(半導体エピ(1),第34回結晶成長国内会議)

25aB10 GaAsのMBE成長におけるリエントラントなRHEED振動の機構(半導体エピ(1),第34回結晶成長国内会議)

RHEED intensities from two-dimensional heteroepitaxial nanoscale systems of GaN on a Si surface

This paper presents a computer program, which facilitates the calculation of changes to the intensity of RHEED oscillations from the heteroepitaxial structures of (0001)GaN films nucleated on a Si surface. The calculations are based on the use of a dynamical diffraction theory and different models of scattering crystal potential. New version program summaryTitle of program: RHEED_DIFF_WProgram Files doi:10.17632/hn3pt6ytky.1Licensing provisions: GNU General Public License 3Programming language used: C++Journal reference of previous version: Computer Physics Communications 185 (2014) 3001–3009Does the new version supersede the previous version?: No. It does supersede version AETW_v1_0.Reasons for the new version: Responding to the users’ feedback we presented a practical procedure of construction of simulation program, which facilitates the calculation of changes to the intensity of RHEED oscillations in the function of the glancing angle of incidence of the electron beam, employing various models of scattering crystal potential for heteroepitaxial structures of hexagonal (0001)GaN films nucleated on a Si surface. GaN has a wurtzite crystal structure with alternating planes of Ga and N atoms and lattice constants a=3.189Å and c=5.185Å [1]. Choosing the top surface to be z=0, the N atoms are located at z=nd where d=5.185/2Å and n is an integer, and Ga atoms are at z=nd−u, where u=3c/8 (as shown in Fig. 1).The nature of physical problem: Since the discovery of molecular beam epitaxy, which allows formation of layers (crystals) with a controlled composition of subsequent monolayers, the research attempts of many laboratories have been focused on studying the dynamics of formation of both monolayers and specific heterojunction structures, that is the structures with monocrystalline interfaces created by materials of various chemical compositions (different physical and chemical properties). The fundamental scientific problem in such research is to specify both interface type and growth mechanism for subsequent layers. Researchers and technologists manufacturing two-dimensional nanoscale systems frequently use RHEED rocking curves (the specular beam intensities versus the glancing angle) to control growth of films at the atomistic level of accuracy. The structural properties of the GaN/Si interface have been meticulously studied by many [3–5], and crucial problem of the direct growth of GaN on Si is the formation of amorphous silicon nitride (SiN) at the GaN/Si interface.Typical running time: The typical running time is machine and user-parameters dependent, i.e. the number of layers for both the substrate and the growing layers included in the calculations.The method of solution: RHEED intensities are calculated within the general framework described in Ref. [2] with the model of the scattering potential for heterostructures: (1)UCombined(z)=∑nUsubstrate(z)+∑n(Ulayer(z)+Uaddlayer(z)), where the Uaddlayer represents the diffuse scattering on the topmost layer.Summary of revisions: The presented version of computer program implements original algorithms of self-consistent calculations for scattering potentials GaN(0001)/Si(111) and solving a time-independent Schrödinger equation for high-energy electrons (Fig. 2). [Display omitted] [Display omitted] [Display omitted] [Display omitted] During the numerical calculations of the changes in the intensity of the specular beam in the function of the glancing angle, it was assumed that the electron energy equals 10 keV, the glancing angle was increased from 0.5° to 7°, and the value of α parameter =0.1 and β=0.5 for the MODEL3 of the scattering potential [2]. Figs. 3–4 present the situation where on the crystalline Si(111) substrate a single GaN layer was placed, where the GaN growth on Si is having a thin amorphous layer. It can be observed that for a very thin layer of GaN, a clear minimal amplitude of RHEED oscillation occurs with the coverage of the GaN layer equal to about 0.5.

Origin of RHEED intensity oscillation during homoepitaxial growth on Si(001)

The origin of RHEED intensity oscillations or variations during growth is analysed by using RHEED intensity distributions calculated from wave functions inside and outside the crystal surface. When the growth proceeds in a layer by layer fashion and the observed intensity is near a diffraction peak, there are only two possible origins of the intensity variations. One is the interference between waves diffracted by the top and the subsequent underlying layers, and the other is the disturbance of the RHEED electron waves by step edges. RHEED rocking curves are computed and the intensities of peaks in the curves are found to vary systematically when material is deposited on the surface. The mechanism of these variations is identified by computing RHEED intensity distributions. An approximate measure of the disturbance of the wave function by step edges is also introduced.

Calculations of parameters of RHEED oscillations using different models of the scattering potential

RHEED intensities for flat and rough surfaces of Ge are computed for off-symmetry azimuths within the framework of dynamical diffraction theory. Two substantially different models of the scattering potential are used. Calculations employing the realistic model are compared with calculations for the simple potential model. The realistic potential is defined with the help of sum of Gaussian functions determined for each atomic layer. On the other hand, in the simple model only two, volume-averaged constants are taken into account to describe the potential (one value is set for the bulk, the other for the growing layer).It is discussed that simplified approaches may be indeed helpful for describing basic features of RHEED oscillations. However, obtaining precise information on growing samples requires the use of realistic approaches.

RHEED Intensity from Vicinal Si(100) Surfaces

RHEED Intensity from Vicinal Si(100) Surfaces

Si(001)表面に対するRHEED入射電子波動場

Auger electron intensity of Si-LVV from Si(001) 2×1 surface has been measured at room temperature (RT) for while changing the glancing angle of incident electron beam of RHEED. Such beam-rocking Auger electron spectroscopy (BRAES) profile shows intensity anomalies at surface wave resonance (SWR) conditions. Surface structure of Si(001) 2×1 has been analyzed by rocking curves of diffraction spots within the 0-th Laue zone. Because, RHEED intensities limited to the 0-th Laue zone can be determined by the projected potential of the Si atomic rows along the incident azimuth and then the phase of asymmetric dimers with flip-flop motion can be neglected. According to the Si(001) 2×1 surface structure model confirmed by the rocking curve analysis, it has been found that the calculated wave-field intensity profile on Si atoms reveals the similar intensity anomalies to those of experimental BRAES profile.

Persistent layer‐by‐layer growth for pulsed‐laser homoepitaxy of $(000\bar 1)$ ZnO

AbstractPersistent layer‐by‐layer growth is demonstrated for pulsed‐laser homoepitaxy of ZnO thin films on $(000\bar 1)$ ZnO single crystals. Employing interval pulsed‐laser deposition (PLD), RHEED oscillations are stabilized over a film thickness of about 90 nm. For interval pulsed laser deposited films a considerably decreased root‐mean‐square surface roughness of 0.26 nm was found, in comparison to 0.74 nm for conventional PLD. A small asymmetry in the X‐ray diffraction (XRD) 2θ –ω scan reveals compressive strain in the thin film being slightly larger for interval PLD as compared to conventional PLD. The FWHM of the photoluminescence (PL) I6 line is higher with about 500 µeV as compared to 350 µeV for the conventional PLD. Consequently, both XRD as well as PL indicate a slightly higher amount of charged defects for the interval PLD.magnified imageEvolution of RHEED intensity as function of time for interval PLD. The green and red line marks the start and the end of the ablation interval, respectively.(© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Physical origin of in-plane lattice spacing oscillations measured by reflection high-energy electron diffraction during epitaxial growth

Intensity oscillations of the specular $(0,0)$ RHEED spot during layer-by-layer growth are well known, whereas the associated oscillation of the position of the RHEED streaks remains more controversial. We revisit the problem of the origin of the peak-to-peak oscillations observed in RHEED spectra during layer-by-layer epitaxial growth. For this purpose we perform solid-on-solid KMC simulations to describe the growth, and we use the kinematical approximation to simulate RHEED intensity profiles. We show that the peak-to-peak oscillations result from the angular dispersion of the incident beam and the periodic oscillation of the size of the growing islands, without the need of invoking the strain relaxation in the islands.

Origin of Reflection High Energy Electron Diffraction Intensity Oscillation during Homoepitaxial Growth on GaAs(001)

The origin of RHEED intensity oscillation during homoepitaxial growth on GaAs(001) is studied on the basis of wave functions calculated with multiple scattering theory. At the most commonly used diffraction condition of glancing angle around 1° and incident electron energy of 15 keV, the origin is not unique and depends on the orientation of the step edges relative to the incident beam azimuth. When the step edges are perpendicular to the incident beam azimuth, the atomic density is the primary origin and the step density is a subsidiary one. When the step edges are parallel to the incident beam azimuth, the step density is the primary origin and the atomic density is a subsidiary one.

Epitaxial growth and electrical transport property of artificial LaNiO 3/LaAlO 3 superlattices

We successfully grew epitaxial LaNiO 3(1 u.c.)/LaAlO 3(1 u.c.) superlattices on single crystal LaAlO 3 (0 0 1) substrates using pulsed laser deposition method. Specular RHEED intensity oscillations were repeated continuously throughout the entire growth. Large angle θ–2 θ X-ray scans show only the peaks from the superlattices and substrates. These results verify the highly qualified crystal structure of the superlattices. The temperature dependence of the resistivity exhibits a semiconducting behavior in the entire temperature range studied. These observations indicate that the semiconducting characteristics of the superlattice are attributed to the radical alteration of the electronic structure of the NiO 2 layers.

Modeling of the hysteretic phenomena in RHEED intensity variation versus temperature for GaAs and InAs surfaces

This paper describes a study of the reflection high energy electron diffraction intensity change against temperature for GaAs and InAs surfaces. The reflection high energy electron diffraction intensity variation against temperature shows different hysteretic characters for the two materials. To date, the explanations for these phenomena were also different for the two substances. Here, we put forward an explanation for these hysteretic phenomena in general terms, applicable to both materials by using the hyperbolic model of hysteresis for coupled systems. Experimental results presented in the paper are in good agreement with the model predictions, supporting the proposed common explanation.

Microstructure of NiFe Epitaxial Thin Films Grown on MgO Single-Crystal Substrates

NiFe epitaxial thin films were prepared on MgO(100) and MgO(110) single-crystal substrates heated at 300° C by ultra-high vacuum molecular beam epitaxy. In the early stage of film growth on MgO(100) substrate, formation of NiFe (112?0) epitaxial thin film with hcp structure is observed by in-situ RHEED. With increasing the film thickness, fcc-NiFe(100) phase appears and the RHEED intensity from fcc-NiFe(100) crystal increases. X-ray diffraction and high-resolution transmission electron microscopy indicate that the resulting film structure is fcc-NiFe(100), suggesting that the metastable hcp-NiFe (112?0) phase is observable only during film growth process. On the contrary, NiFe(110) fcc single-crystal film grows epitaxially on MgO(110) substrate. Atomically sharp boundaries are recognized between NiFe thin films and MgO substrates, where misfit dislocations are periodically introduced in the films at the NiFe/MgO interfaces reducing the lattice mismatches. Out-of-plane and in-plane lattice spacings of these films agree with the values of bulk NiFe crystal with very small errors of less than 0.5%, suggesting that the strains in the NiFe films are very small.

Growth of atomically smooth cubic AlN by molecular beam epitaxy

AbstractIn this work we present the growth of atomically flat c‐AlN layers (surface roughness 0.3 nm RMS) by plasma assisted molecular beam epitaxy (PAMBE) on 3C‐SiC. We develop a model for Al surface kinetics that correlates with RHEED intensity vs. time measurements. We show RHEED patterns and atomic force microscopy (AFM) scans emphasizing the quality of the layers.Ellipsometry yields the dielectric function of c‐AlN around the adsorption edge. The direct gap is obtained with 5.93 eV at room temperature, while the indirect one is below 5.3 eV (onset of adsorption) (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Model-Driven Development for scientific computing. Computations of RHEED intensities for a disordered surface. Part I

Scientific computing is the field of study concerned with constructing mathematical models, numerical solution techniques and with using computers to analyse and solve scientific and engineering problems. Model-Driven Development (MDD) has been proposed as a means to support the software development process through the use of a model-centric approach. This paper surveys the core MDD technology that was used to develop an application that allows computation of the RHEED intensities dynamically for a disordered surface.