Contact Resistance of Symmetrical Contacts of Anisotropic Semiconductor Sample Cut at an Angle to Crystallographic Planes

ALCHEMI (Atom Location by CHanneling Enhanced Microanalysis) enables the site occupancy of atoms in single crystals to be determined. In this article the fundamentals of the method for both EDS and EELS will be discussed. Unlike HRTEM, ALCHEMI does not place stringent resolution requirements on the microscope and, because EDS clearly distinguishes between elements of similar atomic number, it can offer some advantages over HRTEM. It does however, place certain constraints on the crystal. These constraints are: a) the sites of interest must lie on alternate crystallographic planes, b) the projected charge density on the alternate planes must be significantly different, and c) there must be at least one atomic species that lies solely on one of the planes.An electron beam incident on a crystal undergoes elastic scattering; in reciprocal space this is seen as a diffraction pattern and in real space this is a modulation of the electron current across the unit cell. When diffraction is strong (i.e., when the crystal is oriented near to the Bragg angle of a low-order reflection) the electron current at one point in the unit cell will differ significantly from that at another point.

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Zone-axis ALCHEMI for the rapid assessment of site occupancies in garnets

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100144905 ◽

1986 ◽

Vol 44 ◽

pp. 706-707

Author(s):

M.T. Otten ◽

P.R. Buseck

Keyword(s):

Single Crystals ◽

Rapid Assessment ◽

Site Occupancy ◽

Zone Axis ◽

Synthetic Compounds ◽

X Ray ◽

Large Group ◽

Crystallographic Planes

ALCHEMI (Atom Location by CHannelling-Enhanced Microanalysis) is a TEM technique for determining site occupancies in single crystals. The method uses the channelling of incident electrons along specific crystallographic planes. This channelling results in enhanced x-ray emission from the atoms on those planes, thereby providing the required site-occupancy information. ALCHEMI has been applied with success to spinel, olivine and feldspar. For the garnets, which form a large group of important minerals and synthetic compounds, the channelling effect is weaker, and significant results are more difficult to obtain. It was found, however, that the channelling effect is pronounced for low-index zone-axis orientations, yielding a method for assessing site occupancies that is rapid and easy to perform.

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Microstructural Characterization of Au-Ge-Ni based ohmic contacts to GaAs/AlGaAs modfet device

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100126433 ◽

1987 ◽

Vol 45 ◽

pp. 326-327

Author(s):

A.K. Rai ◽

A.K. Petford-Long ◽

A. Ezis ◽

D.W. Langer

Keyword(s):

Contact Resistance ◽

Ohmic Contact ◽

Ohmic Contacts ◽

Microstructural Characterization ◽

Almost Everywhere ◽

Spacer Layer ◽

Good Contact ◽

The Relationship ◽

Lower Contact

Considerable amount of work has been done in studying the relationship between the contact resistance and the microstructure of the Au-Ge-Ni based ohmic contacts to n-GaAs. It has been found that the lower contact resistivity is due to the presence of Ge rich and Au free regions (good contact area) in contact with GaAs. Thus in order to obtain an ohmic contact with lower contact resistance one should obtain a uniformly alloyed region of good contact areas almost everywhere. This can possibly be accomplished by utilizing various alloying schemes. In this work microstructural characterization, employing TEM techniques, of the sequentially deposited Au-Ge-Ni based ohmic contact to the MODFET device is presented.The substrate used in the present work consists of 1 μm thick buffer layer of GaAs grown on a semi-insulating GaAs substrate followed by a 25 Å spacer layer of undoped AlGaAs.

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On the Faceting of Polar Ceramic Surfaces: Microscopy and Holography Studies of MGO(111) Surfaces

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100164295 ◽

1996 ◽

Vol 54 ◽

pp. 366-367

Author(s):

M. Gajdardziska-Josifovska ◽

B. G. Frost ◽

E. Völkl ◽

L. F. Allard

Keyword(s):

Electron Microscopy ◽

High Vacuum ◽

Ultra High Vacuum ◽

Electron Holography ◽

Flat Surfaces ◽

Transmission Electron ◽

Excess Surface ◽

Polar Surfaces ◽

Salt Structure ◽

Crystallographic Planes

Polar surfaces are those crystallographic faces of ionically bonded solids which, when bulk terminated, have excess surface charge and a non-zero dipole moment perpendicular to the surface. In the case of crystals with a rock salt structure, {111} faces are the exemplary polar surfaces. It is commonly believed that such polar surfaces facet into neutral crystallographic planes to minimize their surface energy. This assumption is based on the seminal work of Henrich which has shown faceting of the MgO(111) surface into {100} planes giving rise to three sided pyramids that have been observed by scanning electron microscopy. These surfaces had been prepared by mechanical polishing and phosphoric acid etching, followed by Ar+ sputtering and 1400 K annealing in ultra-high vacuum (UHV). More recent reflection electron microscopy studies of MgO(111) surfaces, annealed in the presence of oxygen at higher temperatures, have revealed relatively flat surfaces stabilized by an oxygen rich reconstruction. In this work we employ a combination of optical microscopy, transmission electron microscopy, and electron holography to further study the issue of surface faceting.

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Degradation Phenomenon of Electrical Contacts by using a Micro-Sliding Mechanism -Modeling about Fluctuation of Contact Resistance-

IEICE Proceeding Series ◽

10.15248/proc.2.6 ◽

2014 ◽

Vol 2 ◽

pp. 6-9

Author(s):

Shin-ichi Wada ◽

Koichiro Sawa

Keyword(s):

Contact Resistance ◽

Electrical Contacts ◽

Sliding Mechanism ◽

Mechanism Modeling

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TEM Studies and Contact Resistance of Au/Ni/Ti/Ta/n-GaN Ohmic Contacts

MRS Proceedings ◽

10.1557/proc-764-c3.17 ◽

2003 ◽

Vol 764 ◽

Cited By ~ 3

Author(s):

D.N. Zakharov ◽

Z. Liliental-Weber ◽

A. Motayed ◽

S.N. Mohammad

Keyword(s):

Contact Resistance ◽

Ohmic Contacts ◽

High Resolution Electron Microscopy ◽

X Ray ◽

Electron Energy Loss Spectrometry ◽

Resolution Electron ◽

Order Of Magnitude ◽

Contact Surfaces ◽

Electron Energy Loss ◽

Magnitude Difference

AbstractOhmic Ta/Ti/Ni/Au contacts to n-GaN have been studied using high resolution electron microscopy (HREM), energy dispersive X-ray spectrometry (EDX) and electron energy loss spectrometry (EELS). Two different samples were used: A - annealed at 7500C withcontact resistance 5×10-6 Ω cm2 and B-annealed at 7750C with contact resistance 6×10-5 Ω cm2. Both samples revealed extensive in- and out-diffusion between deposited layers with some consumption ofGaNlayerand formation of TixTa1-xN50 (0<x<25) at the GaN interface. Almost an order of magnitude difference in contact resistances can be attributed to structure and chemical bonding of Ti-O layers formed on the contact surfaces.

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