7.7. PROBLEMS 349
whereCis in units ofμFandVis in volts. Calculate the built-in voltage and the
depletion width at zero bias. What are the dopant concentrations of the diode?
Problem 7.4In a long basen+pdiode, the slope of theCdif fversusIFplot is
1. 6 × 10 −^5 F/A. Calculate the electron lifetime, the stored charge, and the value of the
diffusion capacitance atIF= 1 mA.
Problem 7.5Consider a Sip+ndiode with a long base. The diode is forward-biased (at
300 K) at a current of 2 mA. The hole lifetime in then-region is 10 −^7 s. Assume that the
depletion capacitance is negligible and calculate the diode impedance at the frequency of
100 KHz, 100 MHz, and 500 MHz.
Problem 7.6Consider a diode with the junction capacitance of 16 pF at zero applied bias
and 4 pF at full reverse bias. The minority carrier time is 2 × 10 −^8 s. If the diode is
switched from a state of forward-bias with current of 2.0 mA to a reverse-bias voltage of
10 V applied through a 5kΩresistance, estimate the response time of the transient.
Problem 7.7Consider a Sip-ndiode at room temperature with following parameters:
Nd = Na=10^17 cm−^3
Dn =20cm^2 /s
Dp =12cm^2 /s
τn = τp=10−^7 s
Calculate the reverse saturation current for a long ideal diode. Also estimate the storage
delay time for the long diode. Now consider a narrow diode made from the structure given
above. The thickness of then-side region is 1.0μm. The thickness of thep-side region is
also 1.0μm. Calculate the reverse saturation current in the narrow diode at a reverse bias
of 2.0 volt. Also estimate the storage delay time for this diode.
Problem 7.8Consider the p-n junction diode shown in figure 7.24. Assume
NA=ND=10^17 cm−^3. Assume that the width of the n-regionL 1 << LPand that the
PN
L2 L1
Figure 7.24: Figure for problem 7.8.
