Sheet (4)
Problems on Semiconductors
1. Determine the concentration of electrons and holes in a sample of Ge at
300o K, which has a concentration of donor atoms =2*1017 cm-3 and
concentration of acceptors atoms = 3*1014 cm-3, is this p-type? ni
=2.5*1013 cm-3, µn= 3800 cm2/ v.sec, and µp = 1800 cm2/ v.sec. Calculate
the conductivity of the sample.
2. Calculate the electrons and holes concentrations and the resistivity of a
silicon crystal containing 1.1*1016 boron atoms / cm3 and 9*1015
phosphorus atoms / cm3 at 27 C0, ni = 1.5*1010 cm-3, µn = 1400 cm2/
v.sec, and µp = 500 cm2/ v.sec.
3. A sample of silicon contains 10-4 atomic percent of phosphorus atoms.
The electron mobility is 0.15 m2/ v.sec. Calculate the extrinsic resistivity
of the sample. (For Si, atomic weight = 28, density = 2300 kg /m3).
4. Find the resistivity of intrinsic Germanium (Ge) at 300 Ko where µn =
3800 cm2/ v.sec, µp =1800 cm2/ v.sec and intrinsic concentration 2.5*1013
cm-3.
5. A sample of n-type germanium (Ge) contains 1023 donor atoms per cubic
meter. Estimate the ratio at room temperature of resistivity of this
material to that of high purity intrinsic germanium, ni=2.5*1019 m-3, µn =
0.38 m2/ v.sec, and µp = 0.18 m2/v.sec.
