Fall 2020
EEM 321 Homework#1
1. (5 points) Describe the main differences between insulators, semiconductors, and conductors?
The main difference is the bandgap. In insulators the bandap is very large; in conductors the bands either
overlap or are partially filled. In semiconductors, the band gap is in between.
2. (15 points) An intrinsic semiconductor has an electron concentration of 1 x 106 cm-3 what it he hole
concentration?
Trick question!! Since semiconductor here is intrinsic no=po=1x106cm-3
3. (15 points) If a Si wafer is doped with 10^8 P (Phosporus) atoms/cm3. Will the Si be n-type, p-type or
intrinsic at room temperature?
At room temperature, ni >>Nd, (1.5x1010 >> 108). So what is no and po?
no = po = ni = 1.51010 so the Si is intrinsic. The doping concentration is too small to make it extrinsic by
definition.
4. (10 points) A Si sample is doped with 1016 As atoms/cm3. What is the equilibrium hole concentration
po at 300K?
As is a donor in Si.
ni=1.5x1010
At 300K, Nd >> ni so, no = Nd =1016 cm-3
po= ni2/no = 2.24 x 104 cm-3
5. (25 points) The two-dimensional representation of the semiconductor GaAs is shown below:
a) If Si atoms are inserted as dopants to GaAs and they replace Ga atoms in the lattice,
will the Si-doped GaAs material be n-type, p-type or still intrinsic? b) If the Si atoms
exclusively replace As atoms, will the Si-doped GaAs material be n-type, p-type or
still intrinsic? Explain.
a) If Si atoms replace Ga atoms within the GaAs lattice, the material will be n-type
because Si has one more valence electron than Ga (which has three valence
electrons). This “extra” valence electron can easily escape the Si atom to become a conduction
electron. (The Si atom becomes positively ionized, as a result.)
b) If Si atoms replace As atoms within the GaAs lattice, the material will be p-type because Si has one
less valence electron than As (which has five valence electrons). An electron from a nearby covalent
