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DEFECTS IN SEMICONDUCTOR CRYSTALS

Defects
Lattice imperfection is called defects. y g g py
Vacancy - is created when an atom moves from its regular site leaving behind an empty site
Substitutional - an impurity may be located at normal lattice sites.
Interstitial - when an atom moves into the interstitial voids in the crystal or impurities are located between normal sites
Frenkel - vacancies & interstitials in close proximity
Schottky - only vacancies are involved- normally created when an atom is removed from the interior to the surface of a crystal. Dislocation - a collection of point defects that results in a line defect/marks the boundary of the region that has slipped with respect to the rest of the crystal/center of distortion. Edge dislocation - a line defect due to a plane of missing atoms or an introduction of an extra plane around which a strain field is developed
Screw dislocation ‐ slipping or gliding of the adjacent planes which manifest as a step at the outer surface, while only a slight lattice deformation exists surrounding the dislocation within the crystal. slight lattice deformation exists surrounding the dislocation within the crystal.
Twins ‐ It is a gross defect that occurs when one part of the crystal forms the mirror image of the other, with the two parts remaining in intimate contact over the bounding surface. The bounding plane of the reflection is known as the twin plane.
Occurs during the crystal growth or mechanical shear of successive plane of atoms. A twinned material may contain high dislocation content.
Inclusions ‐ precipitates near the dislocations or vacancies when point defects are in super saturation. Si crystals may contain precipitation of C, SiO2 and many heavy metals.
Burgers Vector – An error of closure around a dislocation.

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Point Defects
Substitutional larger atom

Vacancy

Frenkel pair

Interstitial

Substitutional smaller atom

Edge dislocations‐Stacking Fault

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Screw Dislocation

Dislocations

Introduction to Semiconductor Materials & Devices by Tyagi p#39‐40 3

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Dislocations Contd.

Introduction to Dislocations by Hull and Bacon,
P#18

Spiral‐Growth
Atomic Force
Microscopic image of f MBE