Unformatted text preview: What are the electron and hole concentrations, n and p, in this sample at room temperature?
[4 pts]
10 cm
2 10 cm
10 cm 10 cm ii) Estimate the resistivity of this sample. [5 pts]
1
1 We can find in the mobility chart using 3 10 cm . Doing so, we find 250 cm /V s
0.25 Ω cm iii) Qualitatively (no calculations required), how would the resistivity change when the
temperature goes up to 100ºC? Explain briefly. [4 pts]
Increasing the temperature will result in more mobile carriers (i.e., more electrons and
holes will have the thermal energy necessary to be conduction electrons/holes), meaning
the resistivity will decrease . Page 2 b) Consider the two Si pn junction diode below: Na=1016 cm3 Nd=1018 cm3 Na=1016 cm3 PN Junction A Nd=1016 cm3 PN Junction B i) Find the ratio of the builtin voltages for these two pn junctions. [4 pts]
ln
ln , , , log , ,
, 10
10
10
log
10 , log /
/ , log 14
12 7
6 ii) What is the ratio of the current densities under a forward bias voltage of 1V for these two
diodes? [4 pts]
(given during exam). As...
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 Spring '07
 KingLiu
 Electrical Engineering, Bipolar junction transistor, cm /V

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