Dislocations are characterized by their Burgers vector and its angle to the dislocation line, and their mobility is provided by glide and climb processes. Most important are edge and screw dislocations, which affect crystal growth and accommodate strain in semiconductors. The mobility of defects is provided by various diffusion mechanisms and affected by their charge. Their creation is interrelated – among each other and also to the presence of extrinsic (impurity) defects – and governed by the conservation of particles and quasi-neutrality. Native point defects and associates of these defects are formed at elevated temperature and may be frozen-in with decreasing temperature. Other defects promote nonradiative carrier recombination, carrier trapping, or excessive carrier scattering and are detrimental to device performance. These defects determine the desired electronic and optical properties of the semiconductor. Some defects are beneficial, such as donors, acceptors, or luminescence centers. They are classified into point, line, and planar defects. Q v = Energy required to produce single vacancy in that solid (J/mole).Semiconducting properties of most interest are predominantly caused by crystal defects. N = Total number of lattice sites per unit volume of solid (lattice sites/m 3). N v = Total number of vacancies per unit volume of solid at a particular temperature (vacancies/m 3). The number of vacancies present within a particular volume of solid at a particular temperature can be mathematically expressed by the following expression: Vacancy defects are temperature sensitive. can also vary due to presence of vacancies.Ĭalculation of number of vacancies in solid: Common physical properties, like melting point, color, etc.It can alter the thermal and electrical resistivity of the solid.Large vacancy concentration can reduce the ductility of the crystalline solid however, can increase the hardness.Although depends on material and its crystal structure, in general, vacancies can decrease the bulk modulus and can increase the Young’s modulus.Due to presence of residual tensile stress within the solid.Due to irradiation or sputtering effect.Number of vacancies in a specific amount of solid increases exponentially as indicated by the expression provided below. Due to increase in temperature of the solid for various processing like heat treatment, coating, etc.For not allowing directional solidification, usually during casting.Vacancy, a point defect, may occur due to various reasons, as enlisted below: With increase in temperature, number of vacancy defects increases exponentially. Any material whose temperature is above absolute zero temperature (0K), can contain vacancies. Vacancy defect can occur in any crystalline solid, in fact, it is inherent. Vacancy defect is caused by loss of one atom from its lattice site. This figure illustrates the difference between a perfect crystal and crystal structure with a vacancy defect. However, hardness of the solid may increase. Due to the reduction in number of atoms in the crystalline solid, vacancy defect results in the reduction of density. Vacancy defect puts the neighboring atoms under tension. Like other point defects, vacancy is also a zero-dimensional defect. So vacancy creates an empty lattice site as depicted below. What is vacancy defect in crystalline solids?Ī vacancy is produced when an atom is missing from its original lattice site. Diamond and Salt are common example of crystalline solid whereas, Wax, Glass, etc. In between there exist Polycrystalline solids, where few different crystal lattices are observed within same solid. If the arrangement of atoms or molecules or ions is highly irregular, then the solid is termed as Amorphous. So crystal lattice is a highly ordered three-dimensional structure of atoms or molecules or ions. Concept of crystalline solid:Ĭrystalline solids are those where atoms or molecules or ions are arranged in a regular pattern (known as crystal lattice) that extends in all directions. Classification of defects in crystalline solid. There are several types of point defects and vacancy is one of them. Point defect is considered as the zero dimensional (0-D) defect, as by mathematical definition, a point is unit-less dimensionless quantity! A point defect occurs when one or more atoms of a crystalline solid leave their original lattice site and/or foreign atoms occupy the interstitial position / lattice site of the crystal. Imperfections or defects in crystalline solid can be broadly classified into four groups, namely, point defect, line defect, surface defect and volume defect.
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