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In semiconductor production, doping intentionally introduces impurities into an extremely pure (also referred to as intrinsic) semiconductor for the purpose of modulating its electrical properties. The impurities are dependent upon the type of semiconductor. Lightly and moderately doped semiconductors are referred to as extrinsic. A semiconductor doped to such high levels that it acts more like a conductor than a semiconductor is referred to as degenerate.
In the context of phosphors and scintillators, doping is better known as activation.
Photon Energy: A photon is the quantum of electromagnetic radiation. The term quantum is the smallest elemental unit of a quantity, or the smallest discrete amount of something. Thus, one quantum of electromagnetic energy is called a photon. The plural of quantum is quanta.
The concept of photons and quanta comes from quantum mechanics and quantum theory. Quantum mechanics is a mathematical model that describes the behavior of particles on an atomic and subatomic scale. It demonstrates that matter and energy are quantized, or come in small discrete bundles, on the smallest scales imaginable. A photon propagates at the speed of light.
The idea of quantum mechanics and photons originated from scientists’ observations of the photoelectric effect. The photoelectric effect is where light striking a metal surface causes electrons to be ejected from the metal. Scientists were unable to explain this phenomenon, but eventually the explanation came from quantum theory.
What they found was that the energy in each quantum of light depends on the frequency of the light. In particular, the energy of a photon equals Planck’s constant times the frequency of the radiation. Mathematically, this is given by the equation E = hf. Planck’s constant is the fundamental constant of quantum theory that determines the scale of the small-scale world. Planck’s constant = 6.63 * 10^-34 joule-second (J-s). The total energy in an electromagnetic wave is the sum of the energies of each photon in the wave.
The energy of a photon is so small that we usually measure it in electronvolts (eV). One eV is the potential energy of each electron in a 1-volt battery. One eV is equal to 1.6 * 10^-19 joules (J). Therefore, we need to convert Planck’s constant to appropriate units, which are electronvolts/hertz (eV/Hz). In eV/Hz, Planck’s constant is 4.136 * 10^15 eV/Hz.
Fermi Level: “Fermi level” is the term used to describe the top of the collection of electron energy levels at absolute zero temperature. This concept comes from Fermi-Dirac statistics. Electrons are fermions and by the Pauli exclusion principle cannot exist in identical energy states.
Photovoltaic Effect: The “photovoltaic effect” is the basic physical process through which a solar cell converts sunlight into electricity. In 1839, nineteen-year-old Edmund Becquerel, a French experimental physicist, discovered the photovoltaic effect while experimenting with an electrolytic cell made up of two metal electrodes.
