ECE 480 – Introduction to Nanotechnology

Emre Yengel

Department of Electrical and Communication Engineering

Fall 2014

Q&A1. (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)

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.

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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.

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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)

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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?

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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-to-valence band electron transitions. Determine the composition of a GaAs–GaP alloy that will emit orange light having a wavelength of 0.60 μm.

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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

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