Section A Self-Test
A1. Consider an n-type silicon in which the dopant concentration ND=1017.
Find the electron and hole concentrations at equilibrium for T=250oK,
300oK, and 350oK.
A2. Find the resistivity of (a) intrinsic silicon and (b) p-type silicon with
NA=1016cm-3. Use ni=1.5x1010cm-3 and assume that for intrinsic
silicon, µn=1350cm2/Vs and µp=480cm2/Vs, and for the doped silicon
µn=1110cm2/Vs and µp=400cm2/Vs.
A3. For a silicon pn junction with NA=1017cm-3 and ND=1016cm-3 find, at
T=300oK, the built-in voltage, the width of the depletion region, and
the distance it extends in the p side and the n side of the junction. Use
ni=1.5x1010cm-3.
A4. In a 10µm long bar of donor-doped silicon, what donor concentration is
needed to realize a drift current density of 1mA/µm2 in response to an
applied voltage of 0.5V? Although the carrier mobilities change with
doping concentration, you may assume µn to be constant and use the
value for intrinsic silicon, 1350cm2/Vs.
A5. Calculate the built-in voltage of a pn junction in which the p and n
regions are doped equally with 1016 atoms/cm3. Assume ni=1010cm-3.
With no external voltage applied, what is the width of the depletion
region, and how far does it extend into the p and n regions? If the
cross-sectional area of the junction is 100µm2, find the magnitude of
the charge stored on either side of the junction.
