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level: Semiconductors and p-n junctions

Questions and Answers List

level questions: Semiconductors and p-n junctions

QuestionAnswer
what are most semi conductors made out ofelements with four outer electrons eg. silicon
what is the structure of bonded atoms with 4 outer electronsthey form a crystal lattice structure where each electron is bonded to another (no free electrons)
what happens if you introduce an atom with 5 outer electrons into a semi conductorthere will still be a lattice structure but one atom will have an additional electron
what is a semi conductor called when it has one extra electronn-type
what can the extra electron in n type semi conductors dodisplace electrons from silicon atoms these electrons can in turn displace other electrons
what happens when an atom of valency three is added to a semi conductorthere is a missing electron in the lattice so this leaves a hole
what is the name of semi conductors where a valence 3 atom has been introducedp-type semi conductor
why do p-type semi conductors conductthe hole appears to move due to electrons moving in the opposite direction, causing the material to conduct
what is dopingthe adding of impurities to pure silicon to produce n-type or p-type silicon
what effect does doping have on the elctrical properties of semi conductorsit increases their conductivity, hence reducing their resistance
what is the charge of n type semiconductorsneutral
what is the overall charge of p type semi conductorsneutral
what is a p-n junctionwhen n type and p type semi conductors are combined one half of the semi conductor is made of p type material, and the other half n-type material
what is a depletion layera region where excess holes from the p type material combine with excess electrons from the n type material (the charges combine)
are there any free charge carriers in the depletion layerno
at a p-n junction what is the charge of the n-type sidethere is a region of positive charge on the n type side
at a p-n junction what is the charge of the p type sidethere is a region of negative charge on the p type side
what is reverse biaswhen a positive voltage is applied to the n type side and a negative voltage is applied to the p type side of the material
what is the effect of reverse bias on the size of the depletion layersize of depletion layer increases
when a p-n junction is reverse biased can any current flow across the junction?no
what is forward biaswhen a negative voltage is applied to the n type side of the material and a positive voltage is applied to the p type side of the material
what is the effect of forward bias on size of the depletion layerdepletion layer shrinks
when a p-n junction is forward bias, can current flow across junction?yes current flows across and junction can conduct
how do leds work?when a p-n junction is forward biased, holes combine with electrons at the junction and release energy. in leds this energy is released as light.
what does the colour of led light depend onthe amount of energy released when electrons and holes combine at a forward biased p-n junction
what is a diodea component which only allows current to flow when connected the right way to a power supply
what is a solar cella semi conductor device that produces a voltage when photons enter the semi conductor junction
what happens when a photon of light enters a solar cell?an electron in the valence band gains enough energy to jump across the energy gap to the conduction band, leaving a hole and creating an e.m.f across the p-n junction
how is an e.m.f created across a pn junctionwhen a photon of light is incident on a photodiode, an electron gains enough energy to move from the valence band to the conduction band electrons then move towards the n type semi conductor, this creates a potential difference this is called the photovoltaic effect
explain in terms of band theory how an led emits lightwhen a voltage is applied to the diode, the electrons move from the conduction band of the n-type semi conductor towards the conduction band of the p-type semi conductor electrons fall from the conduction band to the valence band on either side of the junction photons are emitted