An ideal crystalline solid has a periodic structure that is based on the chemical properties of its constituent atoms (see Chapter 1). However, real crystals are not perfect. They always have imperfections such as extra/missing atoms or impurities, which are called defects. The periodicity characterizes the crystals as we learned in previous Chapters. For example, the periodic potential of the lattice modulates the wavefunction, and we can establish relationships between the energy and wavevector using the Bloch theorem as shown by the Kronig-Penney model (Chapter 4). The existence of defects perturbs the potential of the lattice and this modifies the band diagram in the crystals. While many properties of crystalline systems depend upon the periodic lattice arrangement, many additional properties can be manipulated by adding defects or dopants to the crystal. These properties enable us to fabricate various devices in the modern world of semiconductor technology. On the other hand, unintentionally introduced defects can also have a profound impact on the properties of materials or on the performance of these devices. Therefore it is a challenging goal to have precise control of defects in crystals.
KeywordsPoint Defect Twin Boundary Lattice Mismatch Edge Dislocation Interphase Boundary
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