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Unformatted text preview: p --> high 1/T, etc.
– Plot is for lightly doped, n-type Si • Three regions of interest
– At low temps, donors haven’t yielded all their available
electrons, so donor atoms are in the “ionization” stage,
hence Si is in the ionization region. Also EHP generation
is not that large.
is Figure 3—18
Carrier concentration vs. inverse temperature for Si doped with 1015 donors/cm3. Carrier Concentrations
Electron and Hole Concentrations and Equilibrium
– At moderate temperatures
• dopant is fully ionized - no more electrons to donate
• EHP generation increases as T increases, but is insignificant
relative to number of electrons from donor.
• Called extrinsic region
• n0 insensitive to big changes in T. Excellent for device
operation. – At high temperatures
• no additional electrons from donors
• EHP generation is now significant and begins dominating n 0.
• Si looks “intrinsic” since EHP generation is the dominant
means to create conduction electrons.
means Carrier Concentrations
Compensation • Real semiconductors contain both donors and
acceptor impurities to some degree. This can modify
conduction if the number of unwanted impurity
atoms is significant.
• Fig. 3-19 shows energy bands for compensation in
an n-type conductor.
– Ea is full of electrons because EF >>>...
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- Spring '10