Electronsfeelelectrostaticpote entialofcrys

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Unformatted text preview: about (diffus sion) = fre ee to move in n an electric c field (drift) Fre ee electrons can form an n electrical c current solids: Electrons in s o Collisions with lattice atoms are p possible o Electrons “feel” electrostatic pote ential of crys stal lattice Electrostatic potential in a solid: Chapter 1 – page 6 o Collisions with lattice atoms are minimized in a strictly periodic potential, that is, in a crystalline solid o Influence of the lattice is taken into account by an “effective mass” of electrons Example: me = 9.1 × 10–31 kg (free electron) –32 me* = 6.1 × 10 kg = 0.067 × me (electron in GaAs) Comparison: Crystalline solid versus amorphous solid o High‐purity crystalline solid = high‐technology solid Example: Laser, LED, integrated circuit, microprocessor chip o Amorphous solid = low‐cost solid Example: Amorphous Si solar cell Chapter 1 – page 7 Crystals There are diff ferent types s of solids: o Single e‐crystalline solids o Poly‐c crystalline so olids o A Amorphous s solids o Which h one has the highest mechanical st rength? o Which h one has the highest ele ectrical cond ductivity? o Which h one is easiest to fabric cate? ferent crysta al structures s. Common c crystal struct tures are: There are diff o Simple e cubic cryst tal o Body‐ ‐centered cu ubic crystal o Face‐c centered cub bic crystal o What is the defini ition of the l lattice const tant a0? o What is the defini ition of a unit cell? Chapter 1 – page 8 Crystal growth Crystal growt th … o is an a atom‐by‐ato om assembly y process o is a slo ow process o requir res T >> 300 K for growth Bulk growth of single cry B ystals o Applic cation: Subst trates o Comm mon technique: Growth f from the me elt o Name e of techniqu ue: Czochrals ski techniqu ue (shown in n the figure b below) o Other r...
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