3_1_3semicond_diode

S one way to reduce the spreading found with

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Unformatted text preview: mosphere kept constant per unit volume Dopant deposited on surface ­ constant amount per unit area Ion Implantation of Dopants Ion s s s s One way to reduce the spreading found with diffusion is to use ion One implantation implantation – also gives better uniformity of dopant – yields faster devices – lower temperature process Ions are accelerated from 5 Kev to 10 Mev and directed at silicon – higher energy gives greater depth penetration – total dose is measured by flux » number of ions per cm2 » typically 1012 per cm2 - 1016 per cm2 Flux is over entire surface of silicon – use masks to cover areas where implantation is not wanted Heat afterward to work into crystal lattice Hole and Electron Concentrations Hole To produce reasonable levels of conduction doesn’t To require much doping require – silicon has about 5 x 1022 atoms/cm3 – typical dopant levels are about 1015 atoms/cm3 s In undoped (intrinsic) silicon, the number of holes and In number of free electrons is equal, and their product equals a constant equals – actually, ni increases with increasing temperature s np = n s This equation holds true for doped silicon as well, so This increasing the number of free electrons decreases the number of holes number INTRINSIC (PURE) SILICON INTRINSIC At 0 Kelvin Silicon density is 5*...
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