Current Status of the Quality of 4H-SiC Substrates and Epilayers for Power Device Applications

MRS Advances ◽  
2016 ◽  
Vol 1 (2) ◽  
pp. 91-102 ◽  
Author(s):  
M. Dudley ◽  
H. Wang ◽  
Jianqiu Guo ◽  
Yu Yang ◽  
Balaji Raghothamachar ◽  
...  
Keyword(s):  
Relaxation Process ◽  
Epitaxial Growth ◽  
Driving Force ◽  
Lattice Parameter ◽  
Current Status ◽  
Concentration Difference ◽  
Before And After ◽  
Half Loop ◽  
Device Applications ◽  
Edge Dislocations

ABSTRACTInterfacial dislocations (IDs) and half-loop arrays (HLAs) present in the epilayers of 4H-SiC crystal are known to have a deleterious effect on device performance. Synchrotron X-ray Topography studies carried out on n-type 4H-SiC offcut wafers before and after epitaxial growth show that in many cases BPD segments in the substrate are responsible for creating IDs and HLAs during CVD growth. This paper reviews the behaviors of BPDs in the substrate during the epitaxial growth in different cases: (1) screw-oriented BPD segments intersecting the surface replicate directly through the interface during the epitaxial growth and take part in stress relaxation process by creating IDs and HLAs (Matthews-Blakeslee model [1] ); (2) non-screw oriented BPD half loop intersecting the surface glides towards and replicates through the interface, while the intersection points convert to threading edge dislocations (TEDs) and pin the half loop, leaving straight screw segments in the epilayer and then create IDs and HLAs; (3) edge oriented short BPD segments well below the surface get dragged towards the interface during epitaxial growth, leaving two long screw segments in their wake, some of which replicate through the interface and create IDs and HLAs. The driving force for the BPDs to glide toward the interface is thermal stress and driving force for the relaxation process to occur is the lattice parameter difference at growth temperature which results from the doping concentration difference between the substrate and epilayer.

Evolution of Basal Plane Dislocations during 4H-SiC Epitaxial Growth

2008 ◽  
Vol 600-603 ◽  
pp. 317-320 ◽  
Author(s):  
Robert E. Stahlbush ◽  
Brenda L. VanMil ◽  
Kendrick X. Liu ◽  
Kok Keong Lew ◽  
Rachael L. Myers-Ward ◽  
...  
Keyword(s):  
Epitaxial Growth ◽  
Basal Plane ◽  
Gas Flow ◽  
Epitaxial Layers ◽  
Half Loop ◽  
Edge Dislocations

The evolution of basal plane dislocations (BPDs) in 4H-SiC epitaxy during its growth is investigated by using two types of interrupted growth in conjunction with ultraviolet photoluminescence (UVPL) imaging of the dislocations. For the first, each epitaxial growth was stopped after 10-20 μm and a UVPL map was collected. For the second, changing the gas flow interrupted the growth and the BPDs were imaged at the end. The first sequence made it possible to track the formation of half-loop arrays and show that they arise from BPDs that glide perpendicular to the offcut direction. For both types, each interruption causes between 30 – 50% of the BPDs to be converted to threading edge dislocations (TEDs). This result suggests that using interrupted growth may be an alternate method to producing epitaxial layers with low BPD concentration.

X-ray Topography Studies of Relaxation during the Homo-Epitaxy of 4H-SiC

2015 ◽  
Vol 1741 ◽  
Author(s):  
H. Wang ◽  
M. Dudley ◽  
J. Zhang ◽  
B. Thomas ◽  
G. Chung ◽  
...  
Keyword(s):  
Substrate Surface ◽  
Strain Relaxation ◽  
Lattice Parameter ◽  
Relaxation Processes ◽  
Radial Temperature ◽  
X Ray ◽  
Before And After ◽  
Half Loop ◽  
Mismatch Stress ◽  
Epilayer Surface

ABSTRACTA review is presented of Synchrotron X-ray Topography and KOH etching studies carried out on n type 4H-SiC offcut substrates before and after homo-epitaxial growth to study defect replication and strain relaxation processes and identify the nucleation sources of both interfacial dislocations (IDs) and half-loop arrays (HLAs) which are known to have a deleterious effect on device performance. We show that these types of defects can nucleate during epilayer growth from: (1) short segments of edge oriented basal plane dislocations (BPDs) in the substrate which are drawn by glide into the epilayer; and (2) segments of half loops of BPD that are attached to the substrate surface prior to growth which also glide into the epilayer. It is shown that the initial motion of the short edge oriented BPD segments that are drawn from the substrate into the epilayer is caused by thermal stress resulting from radial temperature gradients experienced by the wafer whilst in the epi-chamber. This same stress also causes the initial glide of the surface half-loop into the epilayer and through the advancing epilayer surface. These mobile BPD segments provide screw oriented segments that pierce the advancing epilayer surface that initially replicate as the crystal grows. Once critical thickness is reached, according to the Mathews-Blakeslee model [1], these screw segments glide sideways under the action of the mismatch stress leaving IDs and HLAs in their wake. The origin of the mismatch stress is shown to be associated with lattice parameter differences at the growth temperature, arising from the differences in doping concentration between substrate and epilayer.

Dislocation Nucleation and Growth in MOCVD GaN/AlN Films on Stepped and Step-free 4H-SiC Mesa Substrates

2008 ◽  
Vol 1090 ◽  
Author(s):  
Mark E. Twigg ◽  
Yoosuf N. Picard ◽  
Nabil D. Bassim ◽  
Joshua D. Caldwell ◽  
Michael A. Mastro ◽  
...  
Keyword(s):  
Dominant Role ◽  
High Stress ◽  
Chemical Vapor ◽  
Misfit Strain ◽  
Nucleation And Growth ◽  
Dislocation Nucleation ◽  
Threading Dislocations ◽  
Surface Steps ◽  
Half Loop ◽  
Edge Dislocations

AbstractUsing transmission electron microscopy, we have analyzed dislocations in AlN nucleation layers and GaN films grown by metallorganic chemical vapor deposition (MOCVD) on the (0001) surface of epitaxially-grown 4H-SiC mesas with and without steps. For 4H-SiC substrates free of SiC surface steps, half-loop nucleation and glide parallel to the AlN/SiC interfacial plane play the dominant role in strain relief, with no mechanism for generating threading dislocations. In contrast, 4H-SiC mesa surfaces with steps give rise to regions of high stress at the heteroepitaxial interface, thereby providing an environment conducive to the nucleation and growth of threading dislocations, which act to accommodate misfit strain by the tilting of threading edge dislocations.

A Pictorial Tracking of Basal Plane Dislocations in SiC Epitaxy

2010 ◽  
Vol 645-648 ◽  
pp. 271-276 ◽  
Author(s):  
Robert E. Stahlbush ◽  
Rachael L. Myers-Ward ◽  
Brenda L. VanMil ◽  
D. Kurt Gaskill ◽  
Charles R. Eddy
Keyword(s):  
Epitaxial Growth ◽  
Basal Plane ◽  
Reduction Process ◽  
Epitaxial Layers ◽  
In Situ Growth ◽  
Half Loop ◽  
Insight Into

The recently developed technique of UVPL imaging has been used to track the path of basal plane dislocations (BPDs) in SiC epitaxial layers. The glide of BPDs during epitaxial growth has been observed and the role of this glide in forming half-loop arrays has been examined. The ability to track the path of BPDs through the epitaxy has made it possible to develop a BPD reduction process for epitaxy grown on 8° offcut wafers, which uses an in situ growth interrupt and has achieved a BPD reduction of > 98%. The images also provide insight into the strong BPD reduction that typically occurs in epitaxy grown on 4° offcut wafers.

Epitaxial growth of the topological insulator Bi2Se3 on Si(111): Growth mode, lattice parameter, and strain state

2013 ◽  
Vol 103 (11) ◽  
pp. 111909 ◽  
Author(s):  
M. Vyshnepolsky ◽  
C. Klein ◽  
F. Klasing ◽  
A. Hanisch-Blicharski ◽  
M. Horn-von Hoegen
Keyword(s):  
Epitaxial Growth ◽  
Topological Insulator ◽  
Strain State ◽  
Lattice Parameter ◽  
Growth Mode

Epitaxial Growth of Ferroelectric Thin Films on GaAs with MgO Buffer Layers by Pulsed Laser Deposition

1991 ◽  
Vol 243 ◽  
Author(s):  
K. Nashimoto ◽  
D. K. Fork ◽  
F. A. Ponce ◽  
T. H. Geballe
Keyword(s):  
Thin Films ◽  
Pulsed Laser Deposition ◽  
Epitaxial Growth ◽  
Pulsed Laser ◽  
Ferroelectric Thin Films ◽  
Buffer Layers ◽  
Laser Deposition ◽  
Hrtem Observation ◽  
Device Applications ◽  
Ferroelectric Hysteresis

AbstractEpitaxial growth of ferroelectric thin films on GaAs (100) by pulsed laser deposition was examined for integrated electro-optic device applications. To promote epitaxy of ferroelectrics and prevent interdiffusion, we have deposited several types of buffer layers. CeO2 reacted strongly with GaAs. Although Y203 9% stabilized-ZrO2 films showed epitaxial growth, YSZ reacted with GaAs at 780°C. MgO grew epitaxially and was stable even at 780°C. HRTEM observation showed a sharp interface between MgO and GaAs. BaTiO3 and SrTiO3 deposited on MgO/GaAs structures showed epitaxial growth. In-plane orientation was BaTiO3 [100 // MgO [100] // GaAs [100]. Epitaxial BaTiO3 films were c-axis oriented tetragonal phase and showed ferroelectric hysteresis.

Effect of the FDA Safety and Innovation Act on racial and gender diversity in neurosurgical device trials

2021 ◽  
pp. 1-8
Author(s):  
Neha Siddiqui ◽  
Ryan G. Chiu ◽  
Ravi S. Nunna ◽  
Georgia Glastris ◽  
Ankit I. Mehta
Keyword(s):  
Clinical Trials ◽  
Native American ◽  
Gender Diversity ◽  
Chi Square ◽  
Clinical Patient ◽  
New Device ◽  
Before And After ◽  
Device Applications ◽  
Us Fda ◽  
And Gender

OBJECTIVE The US FDA uses evidence from clinical trials in its determination of safety and utility. However, these trials have often suffered from limited external validity and generalizability due to unrepresentative study populations with respect to clinical patient demographics. Section 907 of the FDA Safety and Innovation Act (FDASIA) of 2012 attempted to address this issue by mandating the reporting of certain study demographics in new device applications. However, no study has been performed on its effectiveness in the participant diversity of neurosurgical device trials. METHODS The FDA premarket approval (PMA) online database was queried for all original neurosurgical device submissions from January 1, 2006, to December 31, 2019. Endpoints of the study included racial and gender demographics of reported effectiveness trials, which were summated for each submission. Chi-square tests were performed on both endpoints for before and after years of FDASIA passage and implementation. RESULTS A total of 33 device approvals were analyzed, with 14 occurring before SIA implementation and 19 after. Most trials (96.97%) reported gender to the FDA, while 66.67% reported race and 63.64% reported ethnicity. Gender breakdown did not change significantly post-SIA (53.30% female, p = 0.884). Racial breakdown was significantly different from the 2010 US Census for all races (p < 0.001) both pre- and post-SIA. Only Native American race was significantly different in terms of representation post-SIA, increasing from 0% to 0.63% (p = 0.0187). There was no significant change in ethnicity. CONCLUSIONS The FDASIA, as currently written, does not appear to have had a significant impact on the racial or gender diversity of neurosurgical device clinical trial populations. This may be due to the noncompulsory nature of its guidance, or a lack of more stringent regulation on the composition of clinical trials themselves.

scholarly journals Durum Wheat Breeding in the Mediterranean Region: Current Status and Future Prospects

Agronomy ◽  
2020 ◽  
Vol 10 (3) ◽  
pp. 432 ◽  
Author(s):  
Ioannis N. Xynias ◽  
Ioannis Mylonas ◽  
Evangelos G. Korpetis ◽  
Elissavet Ninou ◽  
Aphrodite Tsaballa ◽  
...  
Keyword(s):  
Durum Wheat ◽  
Mediterranean Region ◽  
Seed Quality ◽  
Green Revolution ◽  
Historical Review ◽  
Wheat Breeding ◽  
Molecular Techniques ◽  
Current Status ◽  
Before And After ◽  
The Mediterranean

This brief historical review focuses on durum wheat domestication and breeding in the Mediterranean region. Important milestones in durum wheat breeding programs across the countries of the Mediterranean basin before and after the Green Revolution are discussed. Additionally, the main achievements of the classical breeding methodology are presented using a comparison of old and new cultivars. Furthermore, current breeding goals and challenges are analyzed. An overview of classical breeding methods in combination with current molecular techniques and tools for cultivar development is presented. Important issues of seed quality are outlined, focusing on protein and characteristics that affect human health and are connected with the consumption of wheat end-products.

Ouabain-sensitive liver and diaphragm respiration in cold-acclimated hamster

1977 ◽  
Vol 42 (2) ◽  
pp. 150-153 ◽  
Author(s):  
B. A. Horwitz ◽  
M. Eaton
Keyword(s):  
Transport System ◽  
Cold Exposure ◽  
Driving Force ◽  
Energy Demands ◽  
Before And After ◽  
Ouabain Inhibition ◽  
K Transport

The in vitro respiratory rates of liver and diaphragm from hamsters were compared before and after prolonged cold exposure (5 degrees C, 3–4 wk). In the presence or absence of glucose, respiratory rates were elevated in both tissues from the cold-acclimated hamsters, and these cold-induced increases were significantly reduced by ouabain. This ouabain inhibition is consistent with the hypothesis that cold exposure of these rodents stimulates the energy demands of the Na+/K+ transport system in liver and diaphragm, with these demands providing a driving force, at least in part, for respiration and accompanying cellular thermogenesis.

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