{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

E E 339 - CN12-pn jucntion-steady-state current flow

E E 339 - CN12-pn jucntion-steady-state current flow - 1...

Info iconThis preview shows pages 1–4. Sign up to view the full content.

View Full Document Right Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: 1 P-N Junction: Steady-State Current flow P N Junction: Steady State Current flow 1 Forward and Reverse bias Current flow: qualitative analysis Current flow: quantitative analysi Outline Current flow: quantitative analysis Reverse breakdown Zener breakdown Avalanche breakdown (Other) deviations from simple theory Short diodes (quick note) Summary 2 2 Define a “ forward biased ” p-n junction as one for which a positive voltage V = V f = | V f | is “dropped” from the p-side to n-side … and a “ reverse biased ” p-n junction as one for which a “Forward” and “reverse” bias across a p-n junction … and a reverse biased p n junction as one for which a negative voltage V = – V r = – | V r | is “dropped” from the p-side to the n-side . Consistent with the definition of voltage (V = –E F /q ), the (quasi-) Fermi level near the p-contact will be shifted down (up) by an energy –qV relative to those on the n-side reducing (increasing the “band bending” under forward (reverse bias (increasing) the band bending under forward (reverse) bias . As before, essentially all of the band bending and associated electrostatic potential drop will occur across the charged if now smaller (larger) depletion region … except under very high current flows TBD. 3 Figure 5—13, modified Effects of bias on a p-n junction: transition region width and peak electric field, electrostatic potential ν n,p and energy band diagram (a) equilibrium, (b) forward bias, and (c) reverse bias. note different symbol ( ν n,p ) for electrostatic potential vs. that for voltage ( V ) . 4 3 Total electron current I n consists of a current due to the few electrons incident from the p-side I n, → (that fall into the depletion region and are swept across), which is essentially independent of applied voltage V, … Current flow in a p-n junction: quasi- qualitative analysis which is essentially independent of applied voltage V, … … and a current due to electrons incident from the n-side I n, ← , from the high energy tail of the electron distribution with enough energy to overcome the energy barrier , which is proportional to thermal distribution of electrons (with relative T k qV T k V V q B B o e e ) ( E F,p E c,p E v,p q (voltage ,V) E x E v,n ) ( , , o n c p c V V q E E E F,n V o > V under any conditions for which this diagram is reasonable electrons (with relative numbers of low energy electrons minimized for lack of space.) E c,n 5 The total electron charge current from p to n (direction of voltage “drop”) therefore, is of the form o n T k qV o n n n n I e I I I I B , , , , , , equilibrium values due to electrons from right due to electrons from left In equilibrium, V = 0 and the current must vanish, such that | I n, → ,o | = | I n, ← ,o | ≡ I n,o , so that Similarly for hole current from p to n ) 1 ( , T k qV o n n B e I...
View Full Document

{[ snackBarMessage ]}

Page1 / 27

E E 339 - CN12-pn jucntion-steady-state current flow - 1...

This preview shows document pages 1 - 4. Sign up to view the full document.

View Full Document Right Arrow Icon bookmark
Ask a homework question - tutors are online