NEEP 541 Displacements in Silicon Fall 2002 Jake Blanchard.
-
Upload
harry-higgins -
Category
Documents
-
view
215 -
download
0
Transcript of NEEP 541 Displacements in Silicon Fall 2002 Jake Blanchard.
NEEP 541Displacements in Silicon
Fall 2002Jake Blanchard
Outline Displacements in Silicon
Carrier lifetime Carrier concentration and mobility Annealing
Displacement Effect In addition to ionization,
displacements can affect the performance of semiconductor materials
Displacements tend to affect the carrier lifetime, the carrier concentration, and the carrier mobility
Carrier Lifetime Defined as the average time a carrier
survives before recombination Determined by carrier
concentrations, defect concentrations, and carrier mobility
Irradiation reduces lifetime because it introduces defects which act as recombination sites
Clusters do this more effectively (on a per-defect basis) than point defects
Carrier Concentration and Mobility
Equilibrium conductivity depends on carrier concentration and mobility
Displacements decrease equilibrium concentration by enhancing recombination at defects
Defects also decrease the carrier mobility, largely by the production of ionized impurities leading to enhanced scattering
Again, clustering enhances these effects
Annealing Defects can be removed by heating
the semiconductor Defects recombine and crystal
moves towards its unirradiated state
Time scales are microseconds to hours, depending on temperature
We must reach about 650 K to get significant defect removal
Notes Threshold energy for electron irradiation is
about 150 keV Defect production rates increase rapidly
above about 300 keV Displacement energy for Si is about 12.9 eV Properties are affected by interstitial O in a
Si vacancy There is no known effect from Si interstitials Photons (E<5 MeV) create defects via
Compton electrons