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1.14 eV. Calculate the position of the Fermi level at 200 K and the number of unionised As atoms. me = m h = m. 7. A sample of silicon contains 10 -4 atomic percent of phosphorous donors which are all singly ionized at room temperature. The electron mobility is 0.15 m 2 /Vs. Calculate the extrinsic resistivity of the sample. 8. A sample of n-type Ge contains 10 23 ionized donors per cubic meter. Estimate the ratio at room temperature of the resistivity of this material to that of high-purity intrinsic germanium. The p-n junction (PN) 1. Estimate the ratio of the forward and the reverse biased currents in a p-n junction diode when the applied voltage is 0.5 V. 2. A current of 5 µA flows through a simple p-n junction diode at room temperature when it is reverse biased with 0.15 eV. Calculate the current flow when it is forward biased with the same voltage. 3. In a certain p-n junction at room temperature, the maximum current obtained on reverse bias was 10 µA. What current would be expected to pass through the junction if a forward bias of 0.1 V were applied? 4. Derive an expression for the differential resistance of a p-n junction. How does it vary with temperature when the junction is forward-biased with a certain voltage greater than 4kT/e? Would this device be of any value as a practical thermometer? 6
Superconductors (Su) 1. Determine how great a current strength a long straight superconducting tin wire can tolerate without becoming normal at 2 K. The diameter of the wire is 1 mm. 2. The critical field BC(T) for superconducting tin is determined in a laboratory, that is, the external magnetic field at which the metal goes normal is determined as a function of temperature. The following values were found: T [K] 3.72 3.37 3.27 3.07 2.82 2.50 2.17 1.90 1.52 B C [Tx10 -4 ] 0 54.8 70.0 90.0 129 166 205 227 256 Calculate the value of the critical temperature and the critical field at 0 K from these values. 7
Page 1 and 2: Crystal Structure (CS) 1. A crystal
Page 3 and 4: 5. The value of the electron contri
Page 5: Calculate the band gap under the as
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