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PN Junction Diode ya ku çi ye?

PN Junction Diode

PN junction diode electronics da ku tay componentê sazî ye. Li ser rûna ya wan diodan, yek ji anjîyar hatin bêtirî yên qebûl (P-type) û yek ji an din bêtirî yên daran (N-type). Dioda wek "step graded" an "linearly graded" deket biguheztin.

Li ser PN junction diodeyê step graded, konsantreya bêtirî li heman du taraf derbasdar e hatiye. Li ser linearly graded junction, konsantreya bêtirî bi rêzikên ji hêman hatiye ve dike dibe. Li navend ku vê tey voltage nehat bikar anîn, elektronên azad hatin berdewam kirin tu P-side û hole'kan hatin berdewam kirin tu N-side, ji hehê reyên dikarin.

Atoma qebûlên li vir hatiye tu P-side negatif ionan dehetin û atoma daran li vir hatiye tu N-side pozitif ionan dehetin. Ev electric field ek dike da ku difuziyonê yekem û hole'kan piştrene. Herêmê bi ionên paqij in dike navnîsik da ku depletion region.

Ger forward bias voltage bi bikar anîn p-n junction diode. Ji bo êma ku partî pozitif bataryaya bi P-side hatiye girîng kirin, herêmê depletion width diket gêrder û carrier (hole û elektronên azad) diket girîngkirin ji hêman hatiye. Ger reverse bias voltage bi bikar anîn diode, herêmê depletion width diket mezher û tune charge diket girîngkirin ji hêman hatiye.

P-N Junction Diode Characteristics

Bilînin pn junction ku donor concentration ND û acceptor concentration NA hene. Bilînin da ku hemu atomên donor hatin şandin elektronên azad û pozitif donor ionan dehetin û hemu atomên acceptor hatin qebûl kirin elektron û hole'kan diket veşin û negative acceptor ionan dehetin. Dema ku n û ND û p û NA biyê veşin diket dema ku niha hatin îtal kirin hole û elektronên azad ku ji xwe bi impurities û defects ve şandin.

Ji bo pn junction, elektronên azad ku ji donor atomên hatin şandin tu n-type side hatin difuziyon kirin tu P-type side û recombination bi hole'kan. Bi sîretî, hole'kan ku ji acceptor atomên hatin şandin tu P-type side hatin difuziyon kirin tu N-type side û recombination bi elektronên azad. Pas recombination process, herêmê depletion of charge carriers (elektronên azad û hole'kan) bi hêman hatiye diket. Herêmê ku li vir hatiye charge carriers hatin depletion diket navnîsik da ku depletion region.

Bi navend ku free charge carriers (elektronên azad û hole'kan) nehatin, donor ions tu n-type side û acceptor ions tu p-type side bi hêman hatiye uncovered diket. Ionên pozitif uncovered tu n-type side û ionên negatif uncovered tu p-type side bi hêman hatiye space charge diket. Potential developed bi hêman hatiye wê space charge diket navnîsik da ku diffusion voltage. Diffusion potential across a pn junction diode diket express bikin 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. Ji bo êma diffusion potential prevents charge carriers to cross the junction.

Ev herêm highly resistive diket bi navend ku free charge carriers hatin depletion. Width of the depletion region depends on the applied bias voltage. 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.