# Two semiconductor physics problems with similar data but different solution methods

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.

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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.

• Is this a homework question? – Daniel Dec 21 '17 at 6:05
• 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. – John deo Dec 21 '17 at 6:09
• Do you want me to post the solution for each in the comment here? – John deo Dec 21 '17 at 6:15