Midterm Exam 1 Solutions 08

# I what are the electron and hole concentrations n and

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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 p-n junction diode below: Na=1016 cm-3 Nd=1018 cm-3 Na=1016 cm-3 PN Junction A Nd=1016 cm-3 PN Junction B i) Find the ratio of the built-in voltages for these two p-n 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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