Quantum Field Theory (QFT)
QFT describe the subatomic constituents, the laws and principles applied, and fundamental interaction of nature in physical world (quarks, lepton, gauge bosons, Higgs scalar etc).
- Tan Yu Cao, Conceptual Foundations of QFT
Semiconductor
Semiconductors are materials that have physical properties which are intermediate between those of insulators and metals. This situation makes semiconductor extremely sensitive to imperfections and impurities in the atomic lattice of the crystals. Physicist learned to exploit the sensitivity of semiconductors to the content of foreign atoms in the host lattice. They dope materials with specific impurities which act as donors or acceptors of electron and thus opened the field for developing semiconductor diodes and transistors. Pure semiconductors also have interesting properties.
Ground state electrons in semiconductors are bound to the ions and cannot move freely while electrons in excited state can move freely and not bounded. The ground state and the lowest excited state are separated by an energy gap. When electrons absorb a light quantum (absorb energy), it can be excited across energy gap (become electrons in excited state). The spectral ranges around the energy gap pure semiconductors have been found to exhibit interesting linear and nonlinear optical properties.
- H Haug & Stephan W. Koch, Quantum Theory of the Optical and Electronic Properties of Semiconductors
