Prob 1: Find the conductivity of n-type Ge at room temperature. Assuming one donor atom in each 108 atoms. The density of Ge is 5.32 x 103 kg/m3 and the atomic weight is 72.66 kg/k-mol. Given e=1.6 x 10-19 C, μe=0.38 m2/V-s and μh=0.18 m2/V-s.

Hint: No of Ge atoms per cm3 = 6.023 x 1023 x (atoms/mole) x (1 mole/72.6 g) x (5.32g/cm3) = 4.41 x 1022.

Prob 2: A specimen of germanium at 300 K for which the density of carriers is 2.5 x 1013, is doped with impurity atoms such that there is one impurity atom for 106 germanium atoms. All the impurity atoms may be assumed ionized. The resistivity of doped material is 0.039 Ω-cm. Carreir mobility for germanium at 300 K is 3600 cm2/V-s. For the doped material find the electron and hole concentration.


In order to solve these two problems, we need to get the donor atom concentration. Please tell me how should I find the value of donor concentration in each problem.

  • 1
    \$\begingroup\$ Is this a homework question? \$\endgroup\$ – Daniel Dec 21 '17 at 6:05
  • \$\begingroup\$ No, this is a solved problem from a text book where 2 different methods to find donor concentration is used when the problem data is similar. Which is what I am confused about and asking the experts here to put some light on it...Not posting the solution here on purpose to not affect your judgement. \$\endgroup\$ – John deo Dec 21 '17 at 6:09
  • \$\begingroup\$ Do you want me to post the solution for each in the comment here? \$\endgroup\$ – John deo Dec 21 '17 at 6:15

I was missing the point that the concentration given for Ge in both the problem was different. In 1st prob it was extrinsic concentration and in the 2nd it was intrinsic concentration. The extra information given in the 2nd problem was to confuse the solver on purpose.

  • \$\begingroup\$ So, the information given was to make sure you read the detail - not to confuse you... \$\endgroup\$ – Solar Mike Dec 21 '17 at 8:18
  • \$\begingroup\$ Not really, if you see in both the question degree to doping is mentioned while it is required in only the 1st problem... \$\endgroup\$ – John deo Dec 21 '17 at 8:34
  • \$\begingroup\$ So, as I said “read the detail”... \$\endgroup\$ – Solar Mike Dec 21 '17 at 9:29
  • \$\begingroup\$ The real world isn't set up like a convenient homework question. If information supplied isn't necessary, or necessary information isn't supplied, you don't get to be confused and complain about it and give up. \$\endgroup\$ – user_1818839 Dec 21 '17 at 10:14
  • \$\begingroup\$ @BrianDrummond Sure you do, as long as you don't need employment :) \$\endgroup\$ – Shamtam Dec 21 '17 at 13:36

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