Low-dislocation-density Nonpolar AlN Grown on 4H-SiC (11-20) Substrates

ABSTRACTGrowth of AlN on 4H-SiC (11-20) substrates by plasma-assisted molecular-beam epitaxy is presented. Very high-quality AlN can be grown under a slightly Al-rich condition. Transmission electron microscopy revealed that the AlN layer has 4H crystalline structure with high-phase purity (stacking-fault density is 5×106cm−1) and the density of threading dislocations is as small as 8×107cm−2.

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Epitaxial Growth of Ordered In-Plane Si and Ge Nanowires on Si (001)

Nanomaterials ◽

10.3390/nano11030788 ◽

2021 ◽

Vol 11 (3) ◽

pp. 788

Author(s):

Jian-Huan Wang ◽

Ting Wang ◽

Jian-Jun Zhang

Keyword(s):

Electron Microscopy ◽

Epitaxial Growth ◽

Molecular Beam ◽

Core Shell ◽

High Quality ◽

Quantum Devices ◽

Wafer Scale ◽

Transmission Electron ◽

Controllable Growth

Controllable growth of wafer-scale in-plane nanowires (NWs) is a prerequisite for achieving addressable and scalable NW-based quantum devices. Here, by introducing molecular beam epitaxy on patterned Si structures, we demonstrate the wafer-scale epitaxial growth of site-controlled in-plane Si, SiGe, and Ge/Si core/shell NW arrays on Si (001) substrate. The epitaxially grown Si, SiGe, and Ge/Si core/shell NW are highly homogeneous with well-defined facets. Suspended Si NWs with four {111} facets and a side width of about 25 nm are observed. Characterizations including high resolution transmission electron microscopy (HRTEM) confirm the high quality of these epitaxial NWs.

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Microstructral Investigations on GaN Films Grown by Laser Induced Molecular Beam Epitaxy

MRS Proceedings ◽

10.1557/proc-595-f99w3.58 ◽

1999 ◽

Vol 595 ◽

Cited By ~ 1

Author(s):

H. Zhou ◽

F. Phillipp ◽

M. Gross ◽

H. Schröder

Keyword(s):

Molecular Beam Epitaxy ◽

Molecular Beam ◽

Threading Dislocations ◽

Planar Defects ◽

Sapphire Substrates ◽

Inversion Domain ◽

Transmission Electron ◽

Domain Boundaries ◽

Line Defects ◽

Inversion Domain Boundaries

AbstractMicrostructural investigations on GaN films grown on SiC and sapphire substrates by laser induced molecular beam epitaxy have been performed. Threading dislocations with Burgers vectors of 1/3<1120>, 1/3<1123> and [0001] are typical line defects, predominantly the first type of dislocations. Their densities are typically 1.5×1010 cm−2 and 4×109 cm−2 on SiC and sapphire, respectively. Additionally, planar defects characterized as inversion domain boundaries lying on {1100} planes have been observed in GaN/sapphire samples with an inversion domain density of 4×109 cm−2. The inversion domains are of Ga-polarity with respect to the N-polarity of the adjacent matrix. However, GaN layers grown on SiC show Ga-polarity. Possible reasons for the different morphologies and structures of the films grown on different substrates are discussed. Based on an analysis of displacement fringes of inversion domains, an atomic model of the IDB-II with Ga-N bonds across the boundary was deduced. High resolution transmission electron microscopy (HRTEM) observations and the corresponding simulations confirmed the IDB-II structure determined by the analysis of displacement fringes.

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TEM Study of MOCVD Grown InSb/GaAs Heterostructures with and without TMIn Predeposited Layers

MRS Proceedings ◽

10.1557/proc-340-405 ◽

1994 ◽

Vol 340 ◽

Cited By ~ 1

Author(s):

L. H. Kuo ◽

Susan Z. Hua ◽

L. Salamanca-Riba ◽

D. L. Partin ◽

L. Green ◽

...

Keyword(s):

Vapor Deposition ◽

Chemical Vapor ◽

Organic Chemical ◽

Threading Dislocations ◽

High Quality ◽

Gaas Substrates ◽

Transmission Electron ◽

Metal Organic ◽

Step Growth ◽

Organic Chemical Vapor Deposition

ABSTRACTHigh quality InSb epilayers were grown on GaAs substrates by metal organic chemical vapor deposition using a two-step growth procedure involving trimethal indium (TMIn) predeposition. From transmission electron microscopy studies, we found that an interdiffusion layer of thickness of 10 Å forms at the interface when the substrate is exposed to TMIn for approximately 6 secs prior to the growth of the InSb filns. Hall mobilities up to σ 52,000 cm2/V-s were obtained at 300 K on a 2.1-μm-thick InSb heteroepitaxial film. In contrast, samples without TMIn predeposition showed polycrystallinity of the InSb films grown on single crystalline GaAs substrates. The effect. of TMNIn predeposition is to minimize the misorientation of the grains, suppress the polycrystallinity, decrease the density of threading dislocations, and increase the electron mobilities in the films. However, we found that too much TMIn predeposition gives rise t.o an intermixing layer at the InSb/GaAs interface which deteriorates the film quality. Details of the effect of the TMIn predeposition on the microstructure of InSb/GaAs with different predeposition times (zero, 6, and 12 secs) are discussed.

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The heterogeneous nucleation of threading dislocations on partial dislocations in III-nitride epilayers

Scientific Reports ◽

10.1038/s41598-020-74030-y ◽

2020 ◽

Vol 10 (1) ◽

Author(s):

J. Smalc-Koziorοwska ◽

J. Moneta ◽

P. Chatzopoulou ◽

I. G. Vasileiadis ◽

C. Bazioti ◽

...

Keyword(s):

Heterogeneous Nucleation ◽

Physical Mechanism ◽

Dislocation Nucleation ◽

Threading Dislocation ◽

Threading Dislocations ◽

Physical Mechanisms ◽

Partial Dislocations ◽

Transmission Electron ◽

Device Applications ◽

Very High

Abstract III-nitride compound semiconductors are breakthrough materials regarding device applications. However, their heterostructures suffer from very high threading dislocation (TD) densities that impair several aspects of their performance. The physical mechanisms leading to TD nucleation in these materials are still not fully elucidated. An overlooked but apparently important mechanism is their heterogeneous nucleation on domains of basal stacking faults (BSFs). Based on experimental observations by transmission electron microscopy, we present a concise model of this phenomenon occurring in III-nitride alloy heterostructures. Such domains comprise overlapping intrinsic I1 BSFs with parallel translation vectors. Overlapping of two BSFs annihilates most of the local elastic strain of their delimiting partial dislocations. What remains combines to yield partial dislocations that are always of screw character. As a result, TD nucleation becomes geometrically necessary, as well as energetically favorable, due to the coexistence of crystallographically equivalent prismatic facets surrounding the BSF domain. The presented model explains all observed BSF domain morphologies, and constitutes a physical mechanism that provides insight regarding dislocation nucleation in wurtzite-structured alloy epilayers.

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Low-Temperature Si (111) Homoepitaxy and Doping Mediated by a Monolayer of Pb

MRS Proceedings ◽

10.1557/proc-570-45 ◽

1999 ◽

Vol 570 ◽

Cited By ~ 3

Author(s):

O.D. Dubon ◽

P.G. Evans ◽

J.F. Chervinsky ◽

F. Spaepen ◽

M.J. Aziz ◽

...

Keyword(s):

Molecular Beam ◽

Film Surface ◽

High Quality ◽

Ion Channeling ◽

Promising Strategy ◽

Transmission Electron ◽

Crystalline Films ◽

Si Epitaxy ◽

Deposited Films ◽

Film Interface

ABSTRACTThe codeposition of Pb during Si (111) molecular beam homoepitaxy leads to high-quality crystalline films at temperatures for which films deposited on bare Si (111) are amorphous. Like other growth mediating elements-- commonly called surfactants-- Pb segregates to the film surface. Ion channeling and transmission electron microscopy reveal nearly defect-free epitaxy for a Pb coverage of one monolayer and temperatures as low as 310 °C. We have deposited films up to 1000 Å in thickness with no indication that this is an upper limit for high-quality epitaxy. However, a decrease in the Pb coverage during growth by only one tenth of a monolayer leads to highly defective films at these temperatures. The codeposition of both As and Pb results in a striking enhancement of the film quality as well. In this case, while the Pb again segregates to the film surface, the As is incorporated into the film with no apparent segregation. Lead-mediated Si epitaxy on As-terminated Si (111) produces high-quality films in which the As remains buried at the substrate-film interface. These results show Pb-mediated Si (111) homoepitaxy to be a promising strategy for the synthesis of layered structures having abrupt nanoscale dopant profiles

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Structural Property Study for GeSn Thin Films

Materials ◽

10.3390/ma13163645 ◽

2020 ◽

Vol 13 (16) ◽

pp. 3645

Author(s):

Liyao Zhang ◽

Yuxin Song ◽

Nils von den Driesch ◽

Zhenpu Zhang ◽

Dan Buca ◽

...

Keyword(s):

Electron Microscopy ◽

Thin Films ◽

Transmission Electron Microscopy ◽

Molecular Beam ◽

Chemical Vapor ◽

Threading Dislocations ◽

X Ray Diffraction ◽

Cross Sectional ◽

X Ray ◽

Transmission Electron

The structural properties of GeSn thin films with different Sn concentrations and thicknesses grown on Ge (001) by molecular beam epitaxy (MBE) and on Ge-buffered Si (001) wafers by chemical vapor deposition (CVD) were analyzed through high resolution X-ray diffraction and cross-sectional transmission electron microscopy. Two-dimensional reciprocal space maps around the asymmetric (224) reflection were collected by X-ray diffraction for both the whole structures and the GeSn epilayers. The broadenings of the features of the GeSn epilayers with different relaxations in the ω direction, along the ω-2θ direction and parallel to the surface were investigated. The dislocations were identified by transmission electron microscopy. Threading dislocations were found in MBE grown GeSn layers, but not in the CVD grown ones. The point defects and dislocations were two possible reasons for the poor optical properties in the GeSn alloys grown by MBE.

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Annihilation of Threading Dislocations in Regrown GaN on Electrochemically Etched Nanoporous GaN Template with Optimization of Buffer Layer Growth

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.31.227 ◽

2007 ◽

Vol 31 ◽

pp. 227-229

Author(s):

C.B. Soh ◽

H. Hartono ◽

S.Y. Chow ◽

Soo Jin Chua

Keyword(s):

Electron Microscopy ◽

Buffer Layer ◽

Electrochemical Etching ◽

Layer Growth ◽

Device Fabrication ◽

Buffer Layers ◽

Threading Dislocations ◽

High Quality ◽

Transmission Electron ◽

Gan Buffer Layer

Nanoporous GaN template has been fabricated by electrochemical etching to give hexagonal pits with nano-scale pores of size 20-50 nm in the underlying grains. Electrochemical etching at The effect of GaN buffer layer grown at various temperatures from 650°C to 1015°C on these as-fabricated nano-pores templates are investigated by transmission electron microscopy. The buffer layer grown at the optimized temperature of 850°C partially fill up the pores and voids with annihilation of threading dislocations, serving as an excellent template for high-quality GaN growth. This phenomenon is, however not observed for the samples grown with other temperature buffer layers. The PL spectrum for the regrowth GaN on nanoporous GaN template also shows an enhancement of PL intensity for GaN peak compared to as-grown GaN template, which is indicative of its higher crystal quality. This makes it as a suitable template for subsequent device fabrication.

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Optical properties of GaN with Ga and N polarity

MRS Proceedings ◽

10.1557/proc-693-i10.3.1 ◽

2001 ◽

Vol 693 ◽

Author(s):

M. A. Reshchikov ◽

D. Huang ◽

F. Yun ◽

P. Visconti ◽

T. King ◽

...

Keyword(s):

Molecular Beam ◽

Threading Dislocations ◽

X Ray Diffraction ◽

Cross Sectional ◽

X Ray ◽

Radiative Efficiency ◽

Sapphire Substrates ◽

Transmission Electron ◽

And Inversion

AbstractWe compared photoluminescence (PL) and cross-sectional transmission electron microscopy (TEM) characteristics of GaN samples with Ga and N polarities grown by molecular beam epitaxy (MBE) on sapphire substrates. Ga-polar films grown at low temperature typically have very smooth surfaces, which are extremely difficult to etch with acids or bases. In contrast, the N-polar films have rougher surfaces and can be easily etched in hot H3PO4 or KOH. The quality of the X-ray diffraction spectra is also much better in case of Ga-polar films. Surprisingly, PL efficiency is always much higher in the N-polar GaN, yet the features and shape of the PL spectra are comparable for both polarities. We concluded that, despite the excellent quality of the surface, MBE-grown Ga-polar GaN layers contain higher concentration of nonradiative defects. From the analyses of cross-sectional TEM investigations, we have found that Ga-polar films have high density of threading dislocations (5x109 cm-2) and low density of inversion domains (1x107 cm-2). For N-polar GaN the situation is the reverse: the density of dislocations and inversion domains are 5x108 and ~1x1011 cm-2, respectively. One of the important conclusions derived from the combined PL and TEM study is that inversion domains do not seem to affect the radiative efficiency very adversly, whereas dislocations reduce it significantly.

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Nanorods as a precursor for high quality GaN layers

MRS Proceedings ◽

10.1557/proc-1144-ll18-15 ◽

2008 ◽

Vol 1144 ◽

Author(s):

David Cherns ◽

Ian Griffiths ◽

Somboon Khongphetsak ◽

Sergei Novikov ◽

Nicola Farley ◽

...

Keyword(s):

Molecular Beam Epitaxy ◽

Grain Boundaries ◽

Molecular Beam ◽

Threading Dislocations ◽

High Quality ◽

Threading Defects ◽

Nanorod Growth

ABSTRACTThe density of threading dislocations in GaN/(0001)sapphire films grown by molecular beam epitaxy can be reduced to about 108 cm−2 by growing an intermediate nanorod layer. This paper examines the growth of the nanorods and proposes that threading defects in the overlayer arise either through grain boundaries formed when nanorods coalesce, or through the propagation of dislocation dipoles seen during nanorod growth. Results showing that the latter often terminate or develop into voids during growth are discussed.

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A Method for Preparing Difficult Plant Tissues for Light and Electron Microscopy

Microscopy and Microanalysis ◽

10.1017/s1431927615013756 ◽

2015 ◽

Vol 21 (4) ◽

pp. 902-909 ◽

Cited By ~ 1

Author(s):

Peta L. Clode

Keyword(s):

Electron Microscopy ◽

Light And Electron Microscopy ◽

Plant Tissues ◽

Chemical Fixation ◽

High Quality ◽

Plant Materials ◽

Low Viscosity ◽

Transmission Electron ◽

Plant Sciences ◽

Very High

AbstractAlthough the advent of microwave technologies has both improved and accelerated tissue processing for microscopy, there still remain many limitations in conventional chemical fixation, dehydration, embedding, and sectioning, particularly with regard to plant materials. The Proteaceae, a family of plants widely distributed in the Southern Hemisphere and well adapted to harsh climates and nutrient-poor soils, is a perfect example; the complexity of Proteaceae leaves means that almost no ultrastructural data are available as these are notoriously difficult to both infiltrate and section. Here, a step-by-step protocol is described that allows for the successful preparation ofBanksia prionotes(Australian Proteaceae) leaves for both light and transmission electron microscopy. The method, which applies a novel combination of vibratome sectioning, microwave processing and vacuum steps, and the utilization of an ultra low viscosity resin, results in highly reproducible, well-preserved, sectionable material from which very high-quality light and electron micrographs can be obtained. With this, cellular ultrastructure from the level of a leaf through to organelle substructure can be studied. This approach will be widely applicable, both within and outside of the plant sciences, and can be readily adapted to meet specific sample requirements and imaging needs.

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