Carrier Injection UnderForward Bias在正向偏压下的载流子注入

1、1chapter 6-2. carrier injection under forward biaslast class, we established the excess minority carrier concentration profile under biased conditions.the excess minority carrier concentration at the edge of the depletion layer will increase under forward biased condition. the minimum carrier concen

2、tration decreases exponentially with distance from the depletion layer edge.pne)0()(e)0()(nnppl xl xp xpn xn2carrier injection under forward biasat equilibrium, # of holes diffusing to n-side equals # of holes drifting from n-side. when we apply external forward voltage, va, holes diffusing (injecti

3、on) to n-side from p-side increases exponentially. this increases the hole concentration at the edge of the depletion layer on n-side.ktqvpxpae)(n0nnn0nnnn)()(pxpxp) 1(ean0ktqvp) 1(e)(ap0ppktqvnxnsimilarly, 3minority carrier concentration profile under biasxxpe)0()(nnl xp xpne)0()(ppl xn xnpn = pn0

4、+ pn(x)np= np0 + np(x)pn(0)np(0)np0 + va pn04carrier injection under forward bias (continued)change of axes to x and x (see graph) 1(e(0)an0nktqvppx axispape) 1(ee(0)(nonnl xktqvl xpp xp) 1()0(ap0pktqvennx axisnane) 1(ee)0()(p0ppl xktqvl xnn xn5general current and minority carrier diffusion equation

5、sxpqdqpxjdd)(pppexnqdqnxjdd)(nnnelp22pgpxpdtpln22ngnxndtnsimplified equationsxpqdxjdd)(ppp22p0pxpd6current equations applied to a diode xnqd xjdd)(nn xpqd xjdd)(ppfind jn and jp at the edge of the depletion layer and add them to get the total current.assumption: no generation or recombination inside

6、 the depletion layer.xx7current equations applied to a diodenppddp xqdj e0pnppl/ xpldq e0ddpnn0pl/ xpp xqd ) 1(e0)0(an0ppnpppktqvplqdplqd xjtherefore, 8diode current equations) 1()0(ap0nnnktqvenlqd xjsimilarly,and total current equals, ) 1(eap0nnn0ppktqvnlqdplqdj) 1(a0ktqvejjcurrent due to electrons

7、 will be along positive x direction. shockley equation 9forward and reverse bias characteristicsj) 1(ea0ktqvjjlarge forward bias (va kt/q):ktqvjjae0large reverse bias (va kt/q): 0jj10figure 6.3 is a dimensioned plot of the steady state carrier concentration inside a pn junction diode maintained at room temperature.a.is the diode forward or reverse biased? explainb. do low-level injection conditions prevail in the quasi-neutr