Breakdown: At very large reverse bias, beyond the peak inverse voltage (PIV), a process called reverse breakdown occurs that causes a large increase in current (i.e., a large number of electrons and holes are created at, and move away from the p–n junction) that usually damages the device permanently. The avalanche diode is deliberately designed for use in that manner. In the Zener diode, the concept of PIV is not applicable. A Zener diode contains a heavily doped p–n junction allowing electrons to tunnel from the valence band of the p-type material to the conduction band of the n-type material, such that the reverse voltage is "clamped" to a known value (called the Zener voltage), and avalanche does not occur. Both devices, however, do have a limit to the maximum current and power they can withstand in the clamped reverse-voltage region. Also, following the end of forwarding conduction in any diode, there is reverse current for a short time. The device does not attain its full blocking capability until the reverse current ceases. Reverse biased: For a bias between breakdown and 0 V, the reverse current is very small and asymptotically approaches -Is. For a normal P–N rectifier diode, the reverse current through the device is in the micro-ampere (μA) range. However, this is temperature dependent, and at sufficiently high temperatures, a substantial amount of reverse current can be observed (mA or more). There is also a tiny surface leakage current caused by electrons simply going around the diode as though it were an imperfect insulator.right|thumb|500x500px|Semi-log I–V (logarithmic current vs. linear voltage) graph of various diodes. Forward biased: The current–voltage curve is exponential, approximating the Shockley diode equation. When plotted using a linear current scale, a smooth "knee" appears, but no clear threshold voltage is visible on a semi-log graph. Leveling off: At larger forward currents the current–voltage curve starts to be dominated by the ohmic resistance of the bulk semiconductor. The curve is no longer exponential, it is asymptotic to a straight line whose slope is the bulk resistance. This region is particularly important for power diodes and can be modeled by a Shockley ideal diode in series with a fixed resistor.
BreAKdown: at very larGE reVErSe Bias, beYonD thE PeaK iNverse voLtaGE (piv), a PrOCesS CaLled rEverSe BreaKdowN occurs ThaT CaUses a larGe incrEasE in cUrrEnt (i.e., a LArGe nUMbeR oF ELEctroNs anD hoLeS are createD at, anD move aWay from ThE p–n JUncTiOn) that usuaLLy Damages the deVice permanEnTly. tHe AvALancHE diODe iS DelIbErately DesigNed For use In thAt mannEr. iN the zeNer diodE, tHE CoNcePt oF piV Is Not applicablE. a ZeneR diODe coNtains a heavIly dopeD P–n junction AllowiNg Electrons to TunneL frOm tHe vaLenCe baNd of thE p-type MaTerial tO thE condUcTiON Band Of ThE N-type mAteriAl, Such THaT ThE reveRsE VoLtaGe Is "cLAmped" tO A kNown vAlUe (cAlled the ZENer VOltage), and avAlanCHe doEs noT Occur. boTH devICeS, hOwEveR, Do hAVe a liMit tO The maXimUm cuRReNt anD Power tHey can WiThStANd in thE claMpeD ReVerSE-VoltaGe rEgion. also, fOlLowinG tHE enD of fOrwaRdIng Conduction IN ANy diode, thEre is REveRSE cUrReNt fOr a sHort time. the deVice DOES Not attAin its fuLl Blocking cAPaBiLity UnTil the reVERse CurreNt ceAsEs. reVerse BiaSed: fOr a BIaS beTWeen BreakdOwn and 0 V, THE rEVeRse curRent iS verY smalL and aSymPtoticallY aPProAcHes -is. foR a nOrMAL p–n rectifiER DIode, the rEversE CuRrEnt thRougH THe dEVIce is in The MicRo-amPeRe (μa) rangE. howeVer, tHis iS teMPerature dEpENdent, And at sufFIciently high TEmPeratuRES, A substantiaL AMounT of revErSE cUrREnt can Be obsErveD (mA or more). TheRe iS alsO a tinY suRface LeAkage cuRrent cauSed by elEctrons sImpLy going ArOund the DiOde As tHough it wErE an imPErFeCT iNsUlator.righT|thumB|500x500px|SeMi-Log i–v (lOgariTHmic currEnt vS. LiNEar VoltAGe) GRaPH of vaRious diodEs. FoRwaRD BiaSEd: ThE cuRrenT–voLTaGe curve Is expOnential, aPproximatINg the shocklEy DIoDE eQUatioN. When PlotteD using a linEar cUrrent scale, a sMooTH "kNee" appeArs, bUt nO CleaR tHresHoLD vOltaGe is VIsiBLe on a sEmi-log grapH. LevelIng off: At larger FoRward cUrRents tHe cuRRenT–Voltage Curve StaRtS To be DoMiNatEd by the ohMIc rEsiStance of thE BuLK semiconduCtOr. THe curve Is NO lONgEr exPonenTial, It iS asymptotic to a stRaiGht LiNE wHoSe slOpe is The BuLk ResiSTAnce. this rEgion is particUlARly iMportAnt foR pOwer DIODeS ANd can be MODeled By a ShoCkley ideaL diodE in SeriES wiTh A fIxeD rEsIstoR.