Atomic Ordering of III-V Alloy Semiconductors Grown on (110)InP and its Influence on Electron Mobility

1995 ◽  
Vol 417 ◽  
Author(s):  
O. Ueda
Keyword(s):  
Electron Diffraction ◽  
Growth Surface ◽  
Ordered Structure ◽  
Atomic Ordering ◽  
Ordered Structures ◽  
Limited Mobility ◽  
Alloy Scattering ◽  
Channel Layer ◽  
Diffraction Patterns ◽  
Dimensional Electron Gas

AbstractAtomic ordering in InGaAs, InAlAs, and GaAsSb crystals grown on (110) InP substrates by molecular beam epitaxy, has been studied by transmission electron microscopy. In the electron diffraction pattern from these crystals, superstructure spots associated with CuAu-I type ordered structure are found. When the tilting angle of the substrates increases, the ordering becomes stronger. The ordering is also stronger in crystals grown on substrates tilted toward the <001> or the <001> direction than those on substrates tilted toward the <110> direction. From these results, one can conclude that atomic steps on the growth surface play an important role in the formation of ordered structures. The ordering becomes stronger when the growth temperature increases. In high resolution images of the crystal, doubling in periodicity of 220 and 200 lattice fringes is found, which is associated with CuAu-I type ordered structure. Moreover, anti-phase boundaries are very often observed in the ordered regions. It is also found that ordering is not perfect, and that ordered regions are plate-like microdomains lying on planes slightly tilted from the (110) plane. On the basis of these results together with considerations of the atomic arrangement of the ordered structure and surface reconstruction on the (110) plane, we propose four possible models for the ordering. Through precise evaluation of these models, two models are selected as the most probable ones: these involve formation of the ordered structures on surfaces dominated by two monolayer steps. These models have been experimentally proven by the analyses of electron diffraction patterns from different InGaAs crystals grown on different growth surfaces. We have fabricated InGaAs/N-InAlAs heterostructures with a strongly ordered InGaAs channel layer. The measured two-dimensional electron gas mobilities from these structures are found to be 100,000 cm2/Vs in the <110> direction and 161,000 cm2/Vs in the <110> direction with a sheet electron concentration (Ns) of 9.5 × 1011 cm−2 at 6 K. The latter mobility is much higher than both calculated alloy scattering limited mobility and the best experimental results for lattice-matched InGaAs/N-InA]As systems. The mobility enhancement in the <110> direction is considered to be achieved by the suppression of alloy scattering due to the occurrence of ordering in the InGaAs channel layer.

Planar defects in ordered (Ga,In)P

1988 ◽  
Vol 46 ◽  
pp. 902-903
Author(s):  
S. McKernan ◽  
C. B. Carter ◽  
D. Bour ◽  
J. R. Shealy
Keyword(s):  
Electron Diffraction ◽  
Vapor Phase ◽  
Growth Direction ◽  
High Density ◽  
Ordered Structure ◽  
Planar Defects ◽  
Diffraction Patterns ◽  
Ternary Semiconductors ◽  
Anion Species ◽  
Metallic Vapor

The growth of ternary III-V semiconductors by organo-metallic vapor phase epitaxy (OMVPE) is widely practiced. It has been generally assumed that the resulting structure is the same as that of the corresponding binary semiconductors, but with the two different cation or anion species randomly distributed on their appropriate sublattice sites. Recently several different ternary semiconductors including AlxGa1-xAs, Gaxln-1-xAs and Gaxln1-xP1-6 have been observed in ordered states. A common feature of these ordered compounds is that they contain a relatively high density of defects. This is evident in electron diffraction patterns from these materials where streaks, which are typically parallel to the growth direction, are associated with the extra reflections arising from the ordering. However, where the (Ga,ln)P epilayer is reasonably well ordered the streaking is extremely faint, and the intensity of the ordered spot at 1/2(111) is much greater than that at 1/2(111). In these cases it is possible to image relatively clearly many of the defects found in the ordered structure.

Determination of hydrogen ordering within the β-RH2+xphase (R= Ho, Y) using electron diffraction techniques

2000 ◽  
Vol 33 (5) ◽  
pp. 1246-1252 ◽  
Author(s):  
Elizabeth J. Grier ◽  
Amanda K. Petford-Long ◽  
Roger C. C. Ward
Keyword(s):  
Electron Diffraction ◽  
Neutron Scattering ◽  
Diffraction Pattern ◽  
Computer Simulations ◽  
Fluorite Structure ◽  
Long Range Order ◽  
Hydrogen Atoms ◽  
Ordered Structures ◽  
Diffraction Patterns

Computer simulations of the electron diffraction patterns along the [\bar{1}10] zone axes of four ordered structures within the β-RH2+xphase, withR= Ho or Y, and 0 ≤x≤ 0.25, have been performed to establish whether or not the hydrogen ordering could be detected using electron diffraction techniques. Ordered structures within otherRH2+x(R= Ce, Tb) systems have been characterized with neutron scattering experiments; however, for HoH(D)2+x, neutron scattering failed to characterize the superstructure, possibly because of the lowxconcentration or lack of long-range order within the crystal. This paper aims to show that electron diffraction could overcome both of these problems. The structures considered were the stoichiometric face-centred cubic (f.c.c.) fluorite structure (x= 0), theD1 structure (x= 0.125), theD1astructure (x= 0.2) and theD022structure (x= 0.25). In the stoichiometric structure, with all hydrogen atoms located on the tetrahedral (t) sites, only the diffraction pattern from the f.c.c. metal lattice was seen; however, for the superstoichiometric structures, with the excess hydrogen atoms ordered on the octahedral (o) sites, extra reflections were visible. All the superstoichiometric structures showed extra reflections at the (001)f.c.c.and (110)f.c.c.type positions, with structureD1 also showing extra peaks at (½ ½ ½)f.c.c.. These reflections are not seen in the simulations at similar hydrogen concentrations with the hydrogen atoms randomly occupying theovacancies.

Ordered Structures of Zn1−xFexSe Epilayers Grown on InP and GaAs Substrates

1993 ◽  
Vol 312 ◽  
Author(s):  
K. Park ◽  
H.- Y. Wei ◽  
L. Salamanca-Riba ◽  
B. T. Jonker
Keyword(s):  
Lattice Mismatch ◽  
Misfit Strain ◽  
Growth Direction ◽  
Ordered Structure ◽  
Cross Sectional ◽  
Ordered Structures ◽  
Gaas Substrates ◽  
Lattice Images ◽  
Diffraction Patterns ◽  
Inp Substrates

AbstractWe present evidence for two types of ordered structures, CuAu-I and CuPt, in Zn1−xFexSe (x≈ 0.4) epilayers grown by molecular beam epitaxy. These ordered structures are observed in both electron diffraction patterns and cross-sectional high-resolution lattice images. The CuAu-I ordered structure occurs in Zn1−xFexSe epilayers grown on (001) InP substrates, while the CuPt-type occurs in epilayers grown on (001) GaAs substrates. The ordered structure of Zn1−xFexSe grown on InP substrates consists of alternating ZnSe and FeSe layers along the [001] growth direction and the [110] direction. In contrast, the ordered structure of Zn1−xFexSe grown on GaAs substrates consists of alternating ZnSe and FeSe layers along the < 111 > directions. We have also investigated the role of the misfit strain associated with the lattice mismatch between the epilayers and the substrates on the type of ordered structure.

TEM Evaluation of CuAu-I Type Ordered Structures in MBE grown Ingaas Crystals on (110) Inp Substrates

1990 ◽  
Vol 209 ◽  
Author(s):  
O. Ueda ◽  
Y. Nakata ◽  
T. Nakamura ◽  
T. Fujii
Keyword(s):  
Electron Microscopy ◽  
Molecular Beam ◽  
Growth Surface ◽  
Ordered Structure ◽  
Phase Boundaries ◽  
Ordered Structures ◽  
Transmission Electron ◽  
Tilting Angle ◽  
High Resolution Images ◽  
Inp Substrates

ABSTRACTCuAu-I type ordered structures in InGaAs grown on (110) InP substrates by molecular beam epitaxy, have been studied by transmission electron microscopy. In the electron diffraction pattern from the InGaAs, superstructure spots associated withCuAu-I type ordered structure are found. When the tilting angle of the substrates increases, the ordering becomes stronger. The ordering is also stronger in crystals grown on substrates tilted toward the <001> or the <001> direction than those on substrates tilted toward the <110> direction. From these results, one can conclude that atomic steps on the growth surface play an important role in the formation of ordered structures. The ordering becomes stronger when the growth temperature increases in the range 360-485°C. In high resolution images of the crystal, doubling in periodicity of 220 and 200lattice fringes is found, which is associated with CuAu-I type ordered structure. Moreover, anti-phase boundaries are very often observed in the ordered regions. It is also found that ordering is not perfect, and that ordered regions are plate-like microdomains lying on planes slightly tilted from the (110) plane.

Ordered structure formation in the flux-grown Ba(Mg1/3Ta2/3)O3 single crystals

2001 ◽  
Vol 16 (6) ◽  
pp. 1593-1599 ◽  
Author(s):  
Yu-Chang Lee ◽  
Chen-Chia Chou ◽  
Dah-Shyang Tsai
Keyword(s):  
Electron Diffraction ◽  
Single Crystals ◽  
Annealing Time ◽  
High Resolution Electron Microscopy ◽  
Maximum Intensity ◽  
Ordered Structure ◽  
X Ray Diffraction ◽  
Resolution Electron ◽  
Higher Temperature ◽  
Diffraction Patterns

Formation of ordered structure in flux-grown Ba(Mg1/3Ta2/3)O3(BMT) single crystals was studied using x-ray diffraction, electron diffraction, and high-resolution electron microscopy. The low-temperature-grown crystals exhibited no sign of B-site ordering. Annealing at 1500 °C induced the 1:2 ordered phase, and its content increased with the annealing time. The superlattice diffraction peaks were broad initially; they sharpened rapidly with the annealing time. Diffuse superlattice reflections were found in electron diffraction patterns of 1500 °C annealed BMT; they turned into sharp reflections under long annealing time or higher temperature, 1600 °C. The intensity of diffuse reflections was sparsely distributed, but the maximum intensity location was determined in the digitized recording of image plate. The maximum intensity sites of two diffuse reflections in the 〈111〉 direction deviated from the presumed 1/3 and 2/3 positions and shifted towards the center. The diffuse reflection and the deviation from regular positions were interpreted as the composition modulation during B-site cation diffusion.

Computer Indexing of Electron Diffraction Patterns Including the Effects of Lattice Symmetry

1977 ◽  
Vol 35 ◽  
pp. 22-23
Author(s):  
J. S. Lally ◽  
R. J. Lee
Keyword(s):  
Electron Diffraction ◽  
Zone Axis ◽  
Crystal Thickness ◽  
Double Diffraction ◽  
Automated Method ◽  
Lattice Symmetry ◽  
Intensity Calculations ◽  
Unknown Structure ◽  
Diffraction Patterns ◽  
Orientation Parameters

In the 50 year period since the discovery of electron diffraction from crystals there has been much theoretical effort devoted to the calculation of diffracted intensities as a function of crystal thickness, orientation, and structure. However, in many applications of electron diffraction what is required is a simple identification of an unknown structure when some of the shape and orientation parameters required for intensity calculations are not known. In these circumstances an automated method is needed to solve diffraction patterns obtained near crystal zone axis directions that includes the effects of systematic absences of reflections due to lattice symmetry effects and additional reflections due to double diffraction processes.Two programs have been developed to enable relatively inexperienced microscopists to identify unknown crystals from diffraction patterns. Before indexing any given electron diffraction pattern, a set of possible crystal structures must be selected for comparison against the unknown.

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