Wani aikin PN Junction Diode?

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Misa yana da shi a cikin PN Junction Diode?

PN Junction Diode

PN junction diode shine mafi girma a cikin electronics. A wannan fayilin diode, kowacewa daya na semiconductor ya ci gaba da impurities mai karfi (P-type) kuma kowacewarsu na impurities mai baka (N-type). Ana iya kategorize wannan diode a matsayin 'step graded' ko 'linearly graded' junction.

A cikin PN junction diode na step graded, samun impurities ta zama uniform a duk kofin kofin har zuwa junction. A cikin linearly graded junction, samun impurities ta zama lissafi da kadan a kan kofin junction. Idan babu voltage a faɗa, electrons mai kyau sun zo zuwa P-side kuma holes sun zo zuwa N-side, inda suka haɗa.

Atoms mai karfin da ke P-side a kan junction sun zama negative ions, kuma atoms mai bakar da ke N-side a kan junction sun zama positive ions. Wannan tana taimakawa electric field wanda ya kawo hankali da lafiya ga lafiya ga diffusion daga electrons da holes. Wannan ƙasa da ions mai kyau shine depletion region.

Idan mu faɗa forward bias voltage zuwa p-n junction diode. Yana nufin idan kofin battery mai kyau an sanya zuwa P-side, kafin zaɓe depletion region ya zama ƙarin kuma carriers (holes da free electrons) sun hada tun zuwa junction. Idan mu faɗa reverse bias voltage zuwa diode, zaɓe depletion width ya zama ƙarin kuma ba za a iya hada tun zuwa junction ba.

P-N Junction Diode Characteristics

Babu da tabbacin pn junction da samun donor ND da acceptor NA. Babu da tabbacin cewa duka donor atoms sun taka electrons mai kyau kuma sun zama positive donor ions da duka acceptor atoms sun haɗa electrons kuma sun zama negative acceptor ions. Saboda haka, za a iya cewa samun free electrons (n) da donor ions ND sun fi samun ɗaya kuma samun holes (p) da acceptor ions (NA) sun fi samun ɗaya. A nan, muna yi nasara a kan holes da free electrons da aka haɗa a cikin semiconductors saboda impurities da defects mai kyau.

Tun zuwa pn junction, free electrons da donor atoms suka haɗa a n-type side sun hada zuwa p-typer side kuma suka haɗa da holes. Duk da haka, holes da acceptor atoms suka haɗa a p-type side sun hada zuwa n-type side kuma suka haɗa da free electrons. Ba a nan, ana iya cewa akwai lack of or depletion of charge carriers (free electrons and holes) across the junction. The region across the junction where the free charge carriers get depleted is called depletion region.

Saboda abin da free charge carriers (free electrons and holes), donor ions of n-type side and acceptor ions of p-type side across the junction become uncovered. These positive uncovered donor ions towards n-type side adjacent to the junction and negative uncovered acceptors ions towards p-type side adjacent to the junction cause a space charge across the pn junction. The potential developed across the junction due to this space charge is called the diffusion voltage. The diffusion voltage across a pn junction diode can be expressed as The diffusion potential creates a potential barrier for further migration of free electrons from n-type side to p-type side and holes from p-type side to n-type side. That means diffusion potential prevents charge carriers to cross the junction.

This region is highly resistive because of depletion of free charge carriers in this region. The width of the depletion region depends on the applied bias voltage. The relation between the width of the depletion region and bias voltage can be represented by an equation called Poisson Equation. Here, ε is the permittivity of the semiconductor and V is the biasing voltage. So, on an application of a forward bias voltage the width of the depletion region i.e. pn junction barrier decreases and ultimately disappears.

Hence, in absence of potential barrier across the junction in the forward bias condition free electrons enter into the p-type region and holes enter into the n-type region, where they recombine and release a photon at each recombination. As a result, there will be a forward current flowing through the diode. The current through the PN junction is expressed as Here, voltage V is applied across the pn junction and total current I, flows through the pn junction.

I s is reverse saturation current, e = charge of electron, k is Boltzmann constant and T is temperature in Kelvin scale.

The graph below shows the current-voltage characteristic of a PN junction diode.When, V is positive the junction is forward biased, and when V is negative, the junction is reverse biased. When V is negative and less than VTH, the current is minimal. But when V exceeds VTH, the current suddenly becomes very high. The voltage VTH is known as the threshold or cut in voltage. For Silicon diode VTH = 0.6 V. At a reverse voltage corresponding to the point P, there is abrupt increment in reverse current. This portion of the characteristics is known as breakdown region.