scholarly journals Study of Edge and Screw Dislocation Density in GaN/Al2O3 Heterostructure

Materials ◽  
2019 ◽  
Vol 12 (24) ◽  
pp. 4205 ◽  
Author(s):  
Vladimir Lucian Ene ◽  
Doru Dinescu ◽  
Iulia Zai ◽  
Nikolay Djourelov ◽  
Bogdan Stefan Vasile ◽  
...  
Keyword(s):  
High Resolution ◽  
Dislocation Density ◽  
Screw Dislocation ◽  
Diffusion Length ◽  
Correlation Lengths ◽  
Transmission Electron ◽  
Aln Buffer ◽  
Gan Film ◽  
Defect Densities ◽  
Screw Dislocation Density

This study assesses the characteristics (edge and screw dislocation density) of a commercially available GaN/AlN/Al2O3 wafer. The heterostructure was evaluated by means of high-resolution X-ray diffraction (HR-XRD), high-resolution transmission electron microscopy (HR-TEM), and Doppler-Broadening Spectroscopy (DBS). The results were mathematically modeled to extract defect densities and defect correlation lengths in the GaN film. The structure of the GaN film, AlN buffer, Al2O3 substrate and their growth relationships were determined through HR-TEM. DBS studies were used to determine the effective positron diffusion length of the GaN film. Within the epitaxial layers, defined by a [GaN P 63 m c (0 0 0 2) || P 63 m c AlN (0 0 0 2) || (0 0 0 2) R 3 ¯ c Al2O3] relationship, regarding the GaN film, a strong correlation between defect densities, defect correlation lengths, and positron diffusion length was assessed. The defect densities ρ d e = 6.13 × 1010 cm−2, ρ d s = 1.36 × 1010 cm−2, along with the defect correlation lengths Le = 155 nm and Ls = 229 nm found in the 289 nm layer of GaN, account for the effective positron diffusion length Leff~60 nm.

scholarly journals Defect Structure Determination of GaN Films in GaN/AlN/Si Heterostructures by HR-TEM, XRD, and Slow Positrons Experiments

Nanomaterials ◽  
2020 ◽  
Vol 10 (2) ◽  
pp. 197 ◽  
Author(s):  
Vladimir Lucian Ene ◽  
Doru Dinescu ◽  
Nikolay Djourelov ◽  
Iulia Zai ◽  
Bogdan Stefan Vasile ◽  
...  
Keyword(s):  
High Resolution ◽  
Diffusion Length ◽  
Depth Profiling ◽  
X Ray Diffraction ◽  
Correlation Lengths ◽  
Transmission Electron ◽  
Dislocation Densities ◽  
Elemental Diffusion ◽  
Aln Buffer ◽  
Gan Film

The present article evaluates, in qualitative and quantitative manners, the characteristics (i.e., thickness of layers, crystal structures, growth orientation, elemental diffusion depths, edge, and screw dislocation densities), within two GaN/AlN/Si heterostructures, that alter their efficiencies as positron moderators. The structure of the GaN film, AlN buffer layer, substrate, and their growth relationships were determined through high-resolution transmission electron microscopy (HR-TEM). Data resulting from high-resolution X-ray diffraction (HR-XRD) was mathematically modeled to extract dislocation densities and correlation lengths in the GaN film. Positron depth profiling was evaluated through an experimental Doppler broadening spectroscopy (DBS) study, in order to quantify the effective positron diffusion length. The differences in values for both edge ( ρ d e ) and screw ( ρ d s ) dislocation densities, and correlation lengths (Le, Ls) found in the 690 nm GaN film, were associated with the better effective positron diffusion length (Leff) of L eff GaN 2 = 43 ± 6 nm.

The Use of AlN Interlayers to Improve GaN Growth on A-Plane Sapphire

1999 ◽  
Vol 587 ◽  
Author(s):  
D.D. Koleske ◽  
M.E. Twigg ◽  
A.E. Wickenden ◽  
R.L. Henry ◽  
R.J. Gorman ◽  
...  
Keyword(s):  
Dislocation Density ◽  
Screw Dislocation ◽  
Film Growth ◽  
Fold Increase ◽  
Large Area ◽  
Cross Sectional ◽  
Acceptor Concentration ◽  
Si Doped ◽  
Gan Film ◽  
Screw Dislocation Density

AbstractThe lack of a suitable, lattice matched substrate for the growth of the group III nitrides typically restricts GaN film growth to substrates such as sapphire or SiC, despite the large lattice and thermal mismatch. With the use of AlN or GaN nucleation layers (NL), GaN films of sufficient quality have been produced for blue LEDs. However, for laser and large-area microwave device applications, the large number of dislocations (> 108 cm−2) limit device performance, and techniques are desired to reduce dislocation density during the growth process. Here, we demonstrate how low temperature AlN interlayers (IL) sandwiched between high temperature (HT) GaN layers can be used to improve the electrical, optical, and structural properties of Si doped GaN films. A nearly two-fold increase in mobility is observed in Si doped GaN grown using 5 AlN IL compared to GaN grown on a single AlN NL. For GaN films grown on multiple AlN IL, cross-sectional transmission electron microscopy images reveal a significant reduction in the screw dislocation density and photoluminescence spectra reveal a reduction in yellow band intensity. An analysis of the electrical data based on a single donor/single acceptor model suggests that the improved electron mobility is the result of a reduced acceptor concentration in the top GaN film. The reduction in the calculated acceptor concentration may be associated with the reduction of the screw dislocation density.

scholarly journals Studies of Defect Structure in Epitaxial AlN/GaN Films Grown on (111) 3C-SiC

Nanomaterials ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 1299
Author(s):  
Andreea Bianca Serban ◽  
Vladimir Lucian Ene ◽  
Doru Dinescu ◽  
Iulia Zai ◽  
Nikolay Djourelov ◽  
...  
Keyword(s):  
High Resolution ◽  
Diffusion Length ◽  
X Ray Diffraction ◽  
Correlation Lengths ◽  
Transmission Electron ◽  
Dislocation Densities ◽  
Elemental Diffusion ◽  
20 Nm ◽  
The Relationship

Several aspects such as the growth relation between the layers of the GaN/AlN/SiC heterostructure, the consistency of the interfaces, and elemental diffusion are achieved by High Resolution Transmission Electron Microscopy (HR-TEM). In addition, the dislocation densities together with the defect correlation lengths are investigated via High-Resolution X-ray Diffraction (HR-XRD) and the characteristic positron diffusion length is achieved by Doppler Broadening Spectroscopy (DBS). Moreover, a comparative analysis with our previous work (i.e., GaN/AlN/Si and GaN/AlN/Al2O3) has been carried out. Within the epitaxial GaN layer defined by the relationship (111) 3C-SiC || (0002) AlN || (0002) GaN, the total dislocation density has been assessed as being 1.47 × 1010 cm−2. Compared with previously investigated heterostructures (on Si and Al2O3 substrates), the obtained dislocation correlation lengths (Le = 171 nm and Ls =288 nm) and the mean distance between two dislocations (rd = 82 nm) are higher. This reveals an improved crystal quality of the GaN with SiC as a growth template. In addition, the DBS measurements upheld the aforementioned results with a higher effective positron diffusion length = 75 ± 20 nm for the GaN layer.

Microstructure of Oxidized Ge0.78SiO.12 annealed in a Reducing Ambient

1995 ◽  
Vol 379 ◽  
Author(s):  
N.D. Theodore ◽  
W.S. Liu ◽  
D.Y.C. Lie ◽  
T.K. Cams ◽  
K.L. Wang
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
High Resolution ◽  
Solid Phase ◽  
Solid Phase Epitaxy ◽  
Seeding Layer ◽  
Transmission Electron ◽  
Microstructural Behavior ◽  
Defect Densities

ABSTRACTTransmission electron microscopy, conventional and high-resolution, is used to characterize the microstructural behavior of oxidized Ge0.78Si0.12 layers annealed in a reducing 95% N2+ 5% H2 ambient. An epitaxial Ge layer grows by solid-phase epitaxy on an underlying Ge0.78Si0.12 seeding layer with a Ge-Sio2 matrix positioned between them. Defect densities in the epitaxial Ge are significantly lower than in the underlying Ge0.78Si0.12. Microstructural details of this behavior are investigated.

Microstructural Characterization of an Al-Mg-Si Aluminum Alloy Processed by Equal Channel Angular Pressing

2013 ◽  
Vol 745-746 ◽  
pp. 303-308
Author(s):  
Zhen Zhang ◽  
Man Ping Liu ◽  
Ying Da Yu ◽  
Pål C. Skaret ◽  
Hans Jørgen Roven
Keyword(s):  
Aluminum Alloy ◽  
Electron Microscope ◽  
High Resolution ◽  
Dislocation Density ◽  
Equal Channel Angular Pressing ◽  
Transmission Electron Microscope ◽  
Microstructural Characterization ◽  
Dark Field ◽  
Angular Pressing ◽  
Transmission Electron

In the present work, a peak-aged 6061 Al-Mg-Si aluminum alloy was subjected to equal channel angular pressing (ECAP) at 110 °C. The microstructure of the sample was characterized by high-resolution transmission electron microscope and weak-beam dark-field method. It was shown that the dislocation density in some local areas is much lower than the average dislocation density expected in the usual alloys processed by severe plastic deformation. High-resolution transmission electron microscope observations indicated that many full dislocations were dissociated into partial dislocations connected by stacking faults. In addition, a Z-shaped defect (i.e., a type of dislocation locks) probably formed by the reactions of the partials in different {111} planes was first observed in the ECAPed alloy. Furthermore, the precipitation behavior and sequence in the present ECAPed sample were identified by high-resolution transmission electron microscopy.

Characterization of Porous SiC Substrates and of the Epilayer Structures Grown on Them

2002 ◽  
Vol 742 ◽  
Author(s):  
Balaji Raghothamachar ◽  
Jie Bai ◽  
William M. Vetter ◽  
Perena Gouma ◽  
Michael Dudley ◽  
...  
Keyword(s):  
Dislocation Density ◽  
Optical Microscopy ◽  
Epitaxial Growth ◽  
Screw Dislocation ◽  
Pore Morphology ◽  
Porous Substrate ◽  
X Ray ◽  
Porous Sic ◽  
Screw Dislocation Density

ABSTRACTPorous 6H-SiC and 4H-SiC wafers formed by anodization have been characterized in this study prior to and following the CVD deposition of SiC epitaxial layers, using a combination of synchrotron white beam x-ray topography (SWBXT), SEM, TEM and optical microscopy. Under the high temperatures employed during epitaxial growth, a significant change in pore morphology occurs. While no evidence of reduced screw dislocation density in the epilayers is obtained, a small tilt of the epilayers with respect to the porous substrate observed on x-ray topographs could play a role in limiting penetration of defects from the substrate.

Correlation of threading screw dislocation density to GaN 2‐DEG mobility

2014 ◽  
Vol 50 (23) ◽  
pp. 1722-1724 ◽  
Author(s):  
J.K. Hite ◽  
P. Gaddipati ◽  
D.J. Meyer ◽  
M.A. Mastro ◽  
C.R. Eddy
Keyword(s):  
Dislocation Density ◽  
Screw Dislocation ◽  
Screw Dislocation Density

Study of Dislocation Densities of Thick GaN Films

2014 ◽  
Vol 989-994 ◽  
pp. 387-390
Author(s):  
Yon Gan Li ◽  
Xiang Qian Xiu ◽  
Xue Mei Hua ◽  
Shi Ying Zhang ◽  
Shi Pu Gu ◽  
...  
Keyword(s):  
High Resolution ◽  
Dislocation Density ◽  
Screw Dislocation ◽  
Edge Dislocation ◽  
Thick Films ◽  
X Ray Diffraction ◽  
X Ray ◽  
Dislocation Densities ◽  
Edge Dislocations

The dislocation density of GaN thick films has been measured by high-resolution X-ray diffraction. The results show that both the edge dislocations and the screw dislocation reduce with increasing the GaN thickness. And the edge dislocations have a larger fraction of the total dislocation densities, and the densities for the edge dislocation with increasing thickness reduce less in contrast with those for the screw dislocation.

Dislocation Arrangement in a Thick LEO GaN Film on Sapphire

1999 ◽  
Vol 595 ◽  
Author(s):  
Kathleen A. Dunn ◽  
Susan E. Babcock ◽  
Donald S. Stone ◽  
Richard J. Matyi ◽  
Ling Zhang ◽  
...  
Keyword(s):  
High Resolution ◽  
Electron Diffraction ◽  
Dislocation Density ◽  
Threading Dislocations ◽  
X Ray Diffraction ◽  
Burgers Vector ◽  
X Ray ◽  
The Third ◽  
Dislocation Arrangement ◽  
Gan Film

AbstractDiffraction-contrast TEM, focused probe electron diffraction, and high-resolution X-ray diffraction were used to characterize the dislocation arrangements in a 16[.proportional]m thick coalesced GaN film grown by MOVPE LEO. As is commonly observed, the threading dislocations that are duplicated from the template above the window bend toward (0001). At the coalescence plane they bend back to lie along [0001] and thread to the surface. In addition, three other sets of dislocations were observed. The first set consists of a wall of parallel dislocations lying in the coalescence plane and nearly parallel to the substrate, with Burgers vector (b) in the (0001) plane. The second set is comprised of rectangular loops with b = 1/3 [11 20] (perpendicular to the coalescence boundary) which originate in the coalescence boundary and extend laterally into the film on the (1 100). The third set of dislocations threads laterally through the film along the [1 100] bar axis with 1/3<11 20>-type Burgers vectors These sets result in a dislocation density of ∼109 cm−2. High resolution X-ray reciprocal space maps indicate wing tilt of ∼0.5°.

scholarly journals Quantitative Analysis of the Recovery Process in Pure Iron Using X-ray Diffraction Line Profile Analysis

Materials ◽  
2021 ◽  
Vol 14 (4) ◽  
pp. 895
Author(s):  
Shota Sugiyama ◽  
Toshio Ogawa ◽  
Lei He ◽  
Zhilei Wang ◽  
Yoshitaka Adachi
Keyword(s):  
Quantitative Analysis ◽  
Dislocation Density ◽  
Screw Dislocation ◽  
Edge Dislocation ◽  
Pure Iron ◽  
Annealing Temperature ◽  
Dislocation Core ◽  
Recovery Process ◽  
Line Profile Analysis ◽  
Screw Dislocation Density

We conducted quantitative analysis of the recovery process during pure iron annealing using the modified Williamson-Hall and Warren-Averbach methods. We prepared four types of specimens with different dislocation substructures. By increasing the annealing temperature, we confirmed a decrease in dislocation density. In particular, screw-dislocation density substantially decreased in the early stage of the recovery process, while edge-dislocation density gradually decreased as annealing temperature increased. Moreover, changes in hardness during the recovery process mainly depended on edge-dislocation density. Increases in annealing temperature weakly affected the dislocation arrangement parameter and crystallite size. Recovery-process modeling demonstrated that the decrease in screw-dislocation density during the recovery process was mainly dominated by glide and/or cross-slip with dislocation core diffusion. In contrast, the decrease in edge-dislocation density during the recovery process was governed by a climbing motion with both dislocation core diffusion and lattice self-diffusion. From the above results, we succeeded in quantitatively distinguishing between edge- and screw-dislocation density during the recovery process, which are difficult to distinguish using transmission electron microscope and electron backscatter diffraction.

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