ECE 250 Homework #2
Due 9/15/2008 (Monday).
Problem 1:
A silicon semiconductor is to be designed such that the majority carrier electron concentration is
no=7×1015 cm-3.
a) Should donor or acceptor impurity atoms be added to intrinsic silicon to achieve this electron
concentration?
b) What concentration of dopant impurity atoms is required?
c) In this silicon material, the minority carrier hole concentration is to be no larger than po=106 cm-3.
Determine the maximum allowable temperature.
Problem 2:
The donor concentration in the n-region of a silicon pn diode at 300 °K is Nd = 1017/cm3. The minority
carrier concentration in the p-region is npo=3×103/cm3. The zero bias junction capacitance for this diode
is Cjo=2 pF. Find the junction capacitance with a reverse bias of 10 volts. Assume that m= 0.5.
Problem 3:
A silicon PN diode is operated at 50 °C. The doping concentration on the P-side is 1015/cm3. The doping
concentration on the n-side is 5·1017/cm3. The zero bias junction capacitance is Cjo = 40 pF, and the
grading coefficient is M = 0.5. At what reverse bias voltage will the junction capacitance be equal to
10 pF?
Problem 4:
For the diode of problem 1, Cjo is measured to be 2 pF. Generate a plot of the junction capacitance Cj
versus reverse diode voltage, VR, for V10VmV1 R
≤
≤
. The x-axis should be a log scale for this plot.
Problem 5:
A silicon PN junction diode has a donor doping concentration of Nd=1017/cm3 and an acceptor doping
concentration of Na=1016/cm3. Plot the built-in barrier potential for this diode for temperatures from 0 °C
to 125 °C. Should the y-axis be plotted in a log scale? Why or why not?