ENE 311
Homework # 1
No due date
1. A 10 mm cube of Ge(Germanium) passes a current of 6.4 mA when 10 mV
is applied between two of its parallel faces. Assuming that the charge
m2
, calculate the
V.s
carriers are electrons that have a mobility of 0.39
density of carriers. What is their collision time if the electron’s effective
mass in Ge is 0.12mo where mo is the free electron mass = 9.11 x 10-31 kg.?
Ans: 1.026 x 1021 m-3, 2.66 x 10-13 s
2. Measurements on sodium have provided the following data: resistivity 4.7
x 10-8 ohm-m, and Hall coefficient = -2.5 x 10-10 m3-couloumb-1. Calculate
3
the density of electrons and the mobility. Ans: 2.5 10 m ,5.32 10
28
3
m2
V.s
3. Assume that the mobility of electrons in Si at T = 300 K is µe = 1300
cm2/V-s. Also assume that the mobility is mainly limited by lattice
scattering. Determine the electron mobility at (a) T = 200 K and (b) T =
400 K Ans: 2,388 cm2/V-s, 844 cm2/V-s.
4. Two scattering mechanisms exist in a semiconductor. If only the first
mechanism is present, the mobility will be 250 cm2/V-s. If only the second
mechanism is present, the mobility will be 500 cm2/V-s. Determine the
mobility when both scattering mechanisms exist at the same time. Ans:
167 cm2/V-s.
5. Given a Si sample of unknown doping. Hall measurement provides the
following information: W = 0.05 cm, A = 1.6 x 10-3 cm2, I = 2.5 mA, and the
magnetic field is 0.3 Tesla. If a Hall voltage of 10 mV is measured, find
the Hall coefficient, conductivity type, majority carrier concentration,
resistivity, and mobility of the semiconductor sample. Ans: 426.7 cm3/C,
1.46 x 1016 cm-3, 1.1 -cm, 380 cm2/V-s.
Note: Use the graph in the next page for problem 4