Problemsamling

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?
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