Mid Term Exam
October 25, 2005
An abrupt Si p-n junction has the following properties at 300 oK:
Property | P side | N side | Unit |
Doping | NA = 1018 | ND = 1016 | cm-3 |
Lifetime | tn = 0.1 | tp = 10 | uS |
Mobility | un = 250 | un = 1200 | cm2/V-s |
Mobility | up = 100 | up = 350 | cm2/V-s |
Area = 10-4 cm-2
The width of the N neutral region WN = 3 microns.
The width of the P neutral region WP = 2 microns.
Vbi = VT ln[NAND / ni2] = 0.817VCJ = A[eq ND / 2 Vbi] = 3.1 pF
tb is the base transit time.tb = Q/I = wn2 / 2 Dp
tb = r CDiff
r = VT/I
CDiff = tb I /VT = (3x10-4)2 * 10-3 / 2* 0.0259*440*0.0259 = 150 pF