ECE 480 – Introduction to
Nanotechnology
Emre Yengel
Department of Electrical and
Communication Engineering
Fall 2014
Q&A
1.
(a) Calculate the drift velocity of electrons in germanium at room
temperature and when the magnitude of the electric field is 1000 V/m.
(b) Under these circumstances, how long does it take an electron to
traverse a 25-mm length of crystal? (Consider the room temperature
mobility of electrons in Ge is 0.38 m2/V-s)
a)
b)
Q&A
2. At room temperature the electrical conductivity of PbTe is 500 (Ω-m)-1
, whereas the electron and hole mobilities are 0.16 and 0.075 m2 /V ,
respectively. Compute the intrinsic carrier concentration for PbTe at room
temperature.
Q&A
3. An n-type semiconductor is known to have an electron concentration
of 3 x 1018 m-3. If the electron drift velocity is 100 m/s in an electric
field of 500 V/m, calculate the conductivity of this material.
Q&A
4. Germanium to which 5 x 1022 m-3 As atoms have been added is an
extrinsic semiconductor at room temperature, and virtually all the As
atoms may be thought of as being ionized (i.e., one charge carrier
exists for each As atom). (a) Is this material n-type or p-type? (b)
Calculate the electrical conductivity of this material, assuming
electron and hole mobilities of 0.1 and 0.05 m2/V-s, respectively.
(a) n -type since Sb is a donor in Ge.
(b)
Q&A
5.
A parallel-plate capacitor using a dielectric material having an εr of
2.5 has a plate spacing of 1mm. If another material having
a dielectric constant of 4.0 is used and the capacitance is to be
unchanged, what must be the new spacing between the plates?
Q&A
6.
Gallium arsenide (GaAs) and gallium phosphide (GaP) are compound
semiconductors that have room-temperature band gap energies of 1.42
and 2.25 eV, respectively, and form solid solutions in all proportions.
Furthermore, the band gap of the alloy increases approximately linearly
with GaP additions (in mol%). Alloys of these two materials are used for
light-emitting diodes wherein light is generated by conduction band-tovalence band electron transitions. Determine the composition of a GaAs–
GaP alloy that will emit orange light having a wavelength of 0.60 μm.
Q&A
7.
The intensity of light absorbed while passing through a 16-kilometer
length of optical fiber glass is equivalent to the light intensity
absorbed through for a 25-mm thickness of ordinary window glass.
Calculate the absorption coefficient β of the optical fiber glass if the
value of β for the window glass is 5 × 10–4 mm–1
The fraction of light transmitted through the window glass