Materials {semiconductor}| can have electrons that can move from atom to atom in atomic-orbital conducting bands. Silicon and germanium are semiconductors. Semiconductor compounds include indium gallium arsenide and indium antimonide.
impurities
Semiconductors can be silicon with added gallium {P-type semiconductor} or arsenic {N-type semiconductor}. P-type semiconductors transfer electron vacancies. N-type semiconductors transfer electrons. Holes and electrons must move in opposite directions to complete circuit.
electric charge
If charge touches semiconductor, no change happens, because semiconductor electrons are not free to move.
Impurities {doping}| added to silicon or germanium supply more negative or positive charges, to make more conduction.
donor
Adding material with five electrons in highest orbital {donor impurity} adds extra electron. Antimony, arsenic, and phosphorus are donors {n-type semiconductor}.
acceptor
Adding material that has three electrons in highest orbital {acceptor impurity} results in extra proton {electron deficiency}. Gallium, indium, aluminum, and boron are acceptors {p-type semiconductor}.
junction
If p-type semiconductor touches n-type semiconductor, electrons in n-type semiconductor flow into holes in p-type semiconductor until reaching balance, with voltage across junction. p-type semiconductor has become slightly negative. n-type semiconductor has become slightly positive. No more free charges exist. Junction width is 50 atoms.
diode
If voltage across np junction makes p side positive, current flows greatly, because p side attracts electrons. If voltage across np junction makes p side negative, no current flows, because p side repels electrons. np junctions allow current in only one direction and allow current to be ON or zero OFF, like diodes.
Semiconductors can emit light {electroluminescence}| across pn junctions when current flows. Phosphors can glow if AC current passes through. Machine sprays glass panel with thin transparent metal layer, adds a phosphor layer, and adds thin metal foil. Electroluminescence is efficient and cool but allows only low light levels.
One electron and one hole {exciton} can bind electrostatically for 4 to 40 microseconds, 1150 nanometers apart. Electric forces cause free electrons and holes to drift in opposite directions, at same velocity. Electric force causes average drift velocity per unit force {charge mobility, exciton}. When electron meets hole, they merge. At constant force, ejections and recombinations are in equilibrium.
A thin layer of electrons is between two semiconductors. Near 0 K in high magnetic field [1982], pairs {quasiparticle, pair} of excited superposition of electron states have fractional charges {fractional quantum Hall effect}, with edge effects {edge state}. Fractional quantum Hall effect can extend to four dimensions, as on five-dimensional-sphere surfaces, which have three-dimensional edge states that emerge with relativity. Excitations can carry magnetic-flux units.
Adding electron-deficient materials, with three electrons in highest orbital, results in extra protons, because of electron vacancies {hole}|.
Two semiconductors can have insulator between them {Josephson junction}. Microwaves can supply energy to electron pairs. Voltage V is n = 1/2, 1, 3/3, or 2 times Planck's constant h times frequency f divided by electron charge e: V = (n*h*f) / (2*e). Third semiconductor can supply control current. Control current sets voltage at zero or one, using quantum-mechanical tunneling.
Two semiconductors, or semiconductor and conductor, can meet in region {junction}| 50 molecules thick. Contact point between metal and semiconductor has resistance that does not follow Ohm's law, because current depends on surface properties.
Semiconductors {metal oxide semiconductor} (MOS) can be metal oxides, which can be unipolar, rather than just bipolar.
Solid-state semiconductor circuit elements {transistor, electronic}| amplify current.
types
N-type semiconductor, P-type semiconductor, and N-type semiconductor can join in sandwich {NPN transistor}. P-type semiconductor, N-type semiconductor, and P-type semiconductor can join in sandwich {PNP transistor}. NPN or PNP transistors are bipolar transistors {junction transistor}, with two junctions. Weak signals control current flow. Junction transistors are current operated.
parts
Transistors have cathode emitter, anode collector, and base controller. Collector is between emitter and base. In PNP transistors, electrons flow from emitter to middle collector and from base to middle. In NPN transistors, electrons flow from middle collector to emitter and from middle to base.
process
Holes and electron diffusion across semiconductor np junction continues until electric force equilibrium, preventing further diffusing. Voltage is across emitter and base and across collector and emitter. Applying small positive charge to base attracts electrons and amplifies current 10^5 times. Electron flow from emitter to collector multiplies directly with voltage from base to emitter.
surface barrier
A depletion layer {space charge, transistor} between metal and semiconductor can control conductivity {point contact semiconductor} {surface barrier transistor}.
field effect
Electric field at right angles to silicon surface causes lateral conductance {field-effect transistor}. Insulated field plate can have field that induces conducting surface channel between two surface pn junctions {gate}, as in field-effect transistors, such as metal oxide semiconductors. Field-effect transistors have slow response and high impedance. They are voltage operated, rather than current operated.
electron tubes
Transistors can replace all electron tube types.
In PNP transistors, electrons flow from emitter to collector, and from other sandwich side {base, transistor} to middle.
In PNP transistors, electrons flow from emitter to middle {collector, transistor}, and from base to middle.
In PNP transistors, electrons flow from one sandwich side {emitter, transistor} to collector, and from base to middle.
5-Physics-Electromagnetism-Conductivity
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Date Modified: 2022.0225