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1、Generation and Recombination Currents（产生-复合电流）Reverse-biased generation current01Forward-biased recombination current 02The total forward-biased current03Reverse-biased generation current（反偏产生电流）According to SRH recombination theory,the recombination rates of excess electron and holen and p are elec
2、tron and hole concentrations,Cn and Cp are capture cross sections of electrons and holes,Nt is trap density.For reverse-biased pn junction,there are no mobilized electrons and holes in space charge region,and np0.The negative sign implies a negative recombination rate,called generation rate.uOnce el
3、ectron and hole are generated,they are swept out space charge region.uThe charge flow direction is reverse-biased current direction.The reverse-biased generation current is added to ideal reverse-biased saturation current.The generation process of reverse-biased pn junction.Reverse-biased generation
4、 currentAssuming recombination central energy level is in the position of the intrinsic Fermi energy level,nni and p=pi.According to the definition of lifetime.G is the generation rate in space charge region.p0，n0 are average lifetimes of carriersRecombination rate Reverse-bias generation currentGen
5、eration current density is Assuming generation rate in space charge region is constant.It isThe total reverse-biased current density is the sum of ideal reverse saturation current and reverse generation current.The Js is no relationship with reverse bias,but the Jgen is dependent on depletion layer
6、width,which is the function of reverse-biased voltage.Thus,reverse-biased current density is relating to reverse-biased voltage.Reverse-biased generation currentForward-Bias Recombination Current（正偏复合电流）When pn junction is applied forward bias,electrons and holes can pass across space charge region
7、as excess carriers.It is possible to recombine when electron and hole meet at the space charge region.The recombination rate equation of electron and hole isThe numerator and denominator can be divided with CnCpNt and using lifetime.The energy band diagram of pn junction under forward bias,the intri
8、nsic Ef and quasi-Ef are shown.Efn and Efp are quasi-Ef of electron and hole,respectively.Forward-Bias Recombination CurrentThe dependence of recombination rate on distance,there is a steep peak at the metallurgical junction(x0).Forward-Bias Recombination CurrentThe recombination current density can
9、 be calculated as Jr0：zero-bias recombination current densitySpace charge region in forward-biased pn junction has net carrier recombination.Forward-Bias Recombination CurrentTotal Forward-Bias Current（总正偏电流）Total forward-bias current density is the sum of recombination current density and ideal dif
10、fuse current density.The ideal diffuse current is generated by minority carrier distribution,and it is the function of applied voltage and diffusion length of minority hole.The hole injecting into n region produce above minority distribution.Minority carrier hole concentration in electric neutral n
11、regionTotal forward-biased current density Jr0 is much larger than JsRecombination current densityDiffuse current densityTotal Forward-Bias CurrentWhen current density is low,recombination current is dominating,while diffuse current is dominating for a large current.Total Forward-Bias CurrentThe current-voltage relationship of diode is written asn is ideal factor Under a large forward-bias voltage：n1 Under a small forward-bias voltage：n2 Otherwise：1n2IV curve of forward-biased pn junctionTotal Forward-Bias Current