Determination of as Sticking Coefficients Using Reflection high Energy Electron Diffraction Intensity Oscillations on GaAs

1989 ◽  
Vol 145 ◽  
Author(s):  
Robert Chow ◽  
Rouel Fernandez
Keyword(s):  
Substrate Temperature ◽  
High Energy ◽  
Incorporation Rate ◽  
Sticking Coefficient ◽  
Diffraction Intensity ◽  
Arrhenius Dependence ◽  
As Species ◽  
Substrate Temperatures ◽  
Sticking Coefficients

AbstractRHEED intensity oscillations were used to investigate As-controlled incorporation rates. The measurements were made under Ga accumulation at the surface of the substrate, and at fluxes and substrate temperatures common for 1.0 micron/hr GaAs growth. The results between the dimer and tetramer As species were compared. The transition between Ga and As controlled incorporation rates was constant within 2.5°C for a constant As flux and was independent of the substrate temperature. Also, the As-controlled incorporation rate curves shows two regions as the substrate temperature increases. At low substrate temperatures, the As incorporation rate is substrate temperature independent. Then at higher substrate temperatures, the As incorporation rate has an arrhenius dependence with a positive activation energy. An interpretation of these results is possible by assigning the maximum sticking coefficient of the tetramer to the region where the As incorporation rate is independent of substrate temperature. This assignment allows one to derive the As (dimers and tetramers) sticking coefficient dependence with substrate temperature. The dimer sticking coefficients are greater that the tetramer sticking coefficients for a given substrate temperature and As flux, and the maximum sticking coefficient of the As dimer was determined to be 0.8 in these experiments.

Sticking and Desorption Coefficients of As4 and As2 During Group V and Group III Controlled MBE Growth

1992 ◽  
Vol 263 ◽  
Author(s):  
Rouel Fernandez
Keyword(s):  
Activation Energy ◽  
Flux Ratio ◽  
Growth Conditions ◽  
High Energy ◽  
Controlled Growth ◽  
Sticking Coefficient ◽  
Group V ◽  
Mbe Growth ◽  
Group Iii ◽  
Sticking Coefficients

ABSTRACTReflection High Energy Electron Diffraction (RHEED) oscillations under arsenic and gallium-controlled Molecular Beam Epitaxy (MBE) growth conditions have been used to measure the sticking and desorption coefficients of As2 and As4. The coefficients are obtained from measurements of the arsenic incorporation rates. Comparisons are made with measurements obtained from desorption rates using modulated beam mass spectroscopy. The transition from gallium to arsenic-controlled growth is observed to occur after excess gallium atoms accumulate on the surface. The maximum intrinsic arsenic sticking coefficients occur when the maximum number of gallium atoms can be incorporated for a given arsenic flux. The intrinsic maximum arsenic sticking coefficients are found to be 0.75 and 0.50 for As2 and As4, respectively. During galliumcontrolled growth, the arsenic sticking coefficients are independent of substrate temperature as long as the sticking coefficient of gallium is equal to one. However, a temperature dependent maximum gallium-controlled arsenic sticking coefficient exists. It can be measured by the maximum Ga to As4 flux ratio that produces specular film surfaces. During gallium-controlled growth, the Ga to As flux ratios are shown to be equal to the gallium-controlled arsenic sticking coefficients. The activation energy for arsenic desorption during arsenic-controlled growth conditions was measured as -0.50 eV for independent As4 and As2 incident fluxes. During gallium-controlled growth with incident As4 fluxes, an activation energy for arsenic desorption of -0.70 eV was measured for the maximum gallium-controlled arsenic sticking coefficients.

Microstructural characterization of InGaAs/GaAs quantum wells grown at low substrate temperatures

1991 ◽  
Vol 49 ◽  
pp. 846-847
Author(s):  
C.M. Sung ◽  
B. Elman ◽  
K.J. Ostreicher ◽  
J. Hefter ◽  
Emil S. Koteles
Keyword(s):  
Quantum Wells ◽  
Microstructural Characterization ◽  
High Energy ◽  
Ion Milling ◽  
Cross Sectional ◽  
Usual Manner ◽  
Optical And Electronic Properties ◽  
Pseudomorphic Growth ◽  
Substrate Temperatures

The composition and thickness of InxGa1-xAs/GaAs quantum wells play an important role in the determination of their optical and electronic properties. InxGa1-xAs/GaAs single quantum wells (SQWs) grown at low substrate temperatures with various In compositions (x) and well thicknesses were investigated by reflected high energy electron diffraction (RHEED) and photoluminescence (PL) techniques to determine when the critical thickness for pseudomorphic growth was exceeded. Cross-sectional TEM methods were employed to directly determine the critical layer thickness of InGaAs on GaAs and the presence of the dislocations generated in these layers.The samples were grown by MBE on semi-insulating (100) GaAs substrates at substrate temperatures of 410°C and 460°C. They consisted of undoped SQWs and barriers in which the well width was varied from 1 nm to 22 nm. The In composition in the well layers was varied from 0.3 to 0.5. The growth rates and In compositions were deduced from RHEED intensity oscillation measurements . Cross-sectional specimens for TEM studies were prepared in the usual manner, by mechanical thinning followed by Ar+ ion milling. A Philips EM400T operated at 120 keV was used to observe the specimens.

Initial Stages of Gaas Growth on Scl-XErxas Surfaces

1990 ◽  
Vol 202 ◽  
Author(s):  
Terje G Finstad ◽  
C. J. Palmstrøm ◽  
S. Mounier ◽  
V. G. Keramidas ◽  
J. G. Zhu ◽  
...  
Keyword(s):  
Electron Diffraction ◽  
Substrate Temperature ◽  
Lattice Mismatch ◽  
High Energy ◽  
Energy Electron ◽  
Interference Microscopy ◽  
Strong Tendency ◽  
Moderate Growth ◽  
Substrate Temperatures ◽  
Lattice Matched

ABSTRACTLattice matched ScxEr1-xAs (ScErAs) was grown on GaAs by MBE followed by a GaAs overlayer. The overgrowth of GaAs on ScErAs has been studied by Reflection High Energy Electron Diffraction (RHEED), Low Energy Electron Diffraction (LEED), Auger Electron Spectroscopy (AES), Nomarskii-interference microscopy and Transmission Electron Microscopy (TEM). In this study substrate temperature and crystal orientation have been varied. For GaAs growth on (100)ScErAs there is a strong tendency for island formation and three dimensional (3D) growth. For high substrate temperatures (>500 °C) and for moderate growth rates (10 ML/min) the growth can be described by the Volmer-Weber mode. For lower substrate temperatures we observe that one monolayer of GaAs on ScErAs is metastable. This monolayer shows a (3×1)/(1×3) surface reconstruction. The deposition of more than one monolayer, irrespective of substrate temperature, or the raising of the substrate temperature induces island growth. The metastable reconstructed surface layer of GaAs then partly dissolves into the islands. The strong tendency for 3D growth observed here is very similar to that seen in the growth on ErAs which is not lattice matched to GaAs. This observation demonstrates the significance of electronic bonding mismatch over lattice mismatch for heteroepitaxy between materials with ionic and covalent bonding character. Growth on {111}-polar surfaces yields smoother layers and a stronger tendency for 2D growth.

Analysis of electron-diffraction intensity profiles using a photodiode-array detection system

1983 ◽  
Vol 41 ◽  
pp. 322-323
Author(s):  
J. B. Warren
Keyword(s):  
Electron Diffraction ◽  
Diffraction Pattern ◽  
Detection System ◽  
High Energy ◽  
Photographic Emulsion ◽  
Diffraction Intensity ◽  
Silicon Photodiode ◽  
Photodiode Array Detection ◽  
Analog To Digital ◽  
Photodiode Array

Electron diffraction intensity profiles have been used extensively in studies of polycrystalline and amorphous thin films. In previous work, diffraction intensity profiles were quantitized either by mechanically scanning the photographic emulsion with a densitometer or by using deflection coils to scan the diffraction pattern over a stationary detector. Such methods tend to be slow, and the intensities must still be converted from analog to digital form for quantitative analysis. The Instrumentation Division at Brookhaven has designed and constructed a electron diffractometer, based on a silicon photodiode array, that overcomes these disadvantages. The instrument is compact (Fig. 1), can be used with any unmodified electron microscope, and acquires the data in a form immediately accessible by microcomputer.Major components include a RETICON 1024 element photodiode array for the de tector, an Analog Devices MAS-1202 analog digital converter and a Digital Equipment LSI 11/2 microcomputer. The photodiode array cannot detect high energy electrons without damage so an f/1.4 lens is used to focus the phosphor screen image of the diffraction pattern on to the photodiode array.

Kinematic Approximations in TED and RHEED Analysis of Reconstructed Surfaces

1990 ◽  
Vol 48 (2) ◽  
pp. 396-397
Author(s):  
L. -M. Peng ◽  
M. J. Whelan
Keyword(s):  
Electron Diffraction ◽  
Kinematic Analysis ◽  
Incident Beam ◽  
High Energy ◽  
Energy Electron ◽  
Great Success ◽  
High Energy Electron ◽  
Kinematic Approximation ◽  
Reconstructed Surfaces

In recent years there has been a trend in the structure determination of reconstructed surfaces to use high energy electron diffraction techniques, and to employ a kinematic approximation in analyzing the intensities of surface superlattice reflections. Experimentally this is motivated by the great success of the determination of the dimer adatom stacking fault (DAS) structure of the Si(111) 7 × 7 reconstructed surface.While in the case of transmission electron diffraction (TED) the validity of the kinematic approximation has been examined by using multislice calculations for Si and certain incident beam directions, far less has been done in the reflection high energy electron diffraction (RHEED) case. In this paper we aim to provide a thorough Bloch wave analysis of the various diffraction processes involved, and to set criteria on the validity for the kinematic analysis of the intensities of the surface superlattice reflections.The validity of the kinematic analysis, being common to both the TED and RHEED case, relies primarily on two underlying observations, namely (l)the surface superlattice scattering in the selvedge is kinematically dominating, and (2)the superlattice diffracted beams are uncoupled from the fundamental diffracted beams within the bulk.

Observations on the growth of barium bismuth oxide thin films

1992 ◽  
Vol 50 (1) ◽  
pp. 76-77
Author(s):  
M G. Norton ◽  
E.S. Hellman ◽  
E.H. Hartford ◽  
C.B. Carter
Keyword(s):  
Substrate Temperature ◽  
Deposition Process ◽  
Nucleation Layer ◽  
Second Stage ◽  
Device Applications ◽  
High Transition ◽  
Substrate Temperatures ◽  
Oriented Material ◽  
Barium Bismuth ◽  
Superconductor Device

The bismuthates (for example, Ba1-xKxBiO3) represent a class of high transition temperature superconductors. The lack of anisotropy and the long coherence length of the bismuthates makes them technologically interesting for superconductor device applications. To obtain (100) oriented Ba1-xKxBiO3 films on (100) oriented MgO, a two-stage deposition process is utilized. In the first stage the films are nucleated at higher substrate temperatures, without the potassium. This process appears to facilitate the formation of the perovskite (100) orientation on (100) MgO. This nucleation layer is typically between 10 and 50 nm thick. In the second stage, the substrate temperature is reduced and the Ba1-xKxBiO3 is grown. Continued growth of (100) oriented material is possible at the lower substrate temperature.

scholarly journals Thermal Dynamic Behavior in Bi-Zone Habitable Cell with and without Phase Change Materials

Proceedings ◽  
2020 ◽  
Vol 63 (1) ◽  
pp. 41
Author(s):  
Hanae El Fakiri ◽  
Lahoucine Ouhsaine ◽  
Abdelmajid El Bouardi
Keyword(s):  
Thermal Behavior ◽  
Thermal Comfort ◽  
Phase Change ◽  
Dynamic Behavior ◽  
Phase Change Materials ◽  
Energy Performance ◽  
High Energy ◽  
Water Heater ◽  
Simplified Modeling

The thermal dynamic behavior of buildings represents an important aspect of the energy efficiency and thermal comfort of the indoor environment. For this, phase change material (PCM) wallboards integrated into building envelopes play an important role in stabilizing the temperature of the human comfort condition. This article provides an assessment of the thermal behavior of a “bi-zone” building cell, which was built based on high-energy performance (HEP) standards and heated by a solar water heater system through a hydronic circuit. The current study is based on studying the dynamic thermal behavior, with and without implantation of PCMs on envelope structure, using a simplified modeling approach. The evolution of the average air temperature was first evaluated as a major indicator of thermal comfort. Then, an evaluation of the thermal behavior’s dynamic profile was carried out in this study, which allowed for the determination of the PCM rate anticipation in the thermal comfort of the building cell.

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