3_1_3semicond_diode

Battery applied very little electric current flows

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Unformatted text preview: loose” electrons – at room temperature, if at battery applied, very little electric current flows flows Conduction in Crystal Lattices Conduction s s s Semiconductors (Si and Ge) have 4 electrons in their outer shell – 2 in the s subshell – 2 in the p subshell As the distance between atoms decreases the discrete subshells As spread out into bands spread As the distance decreases further, the bands overlap and then As separate separate – the subshell model doesn’t hold anymore, and the electrons the can be thought of as being part of the crystal, not part of the atom atom – 4 possible electrons in the lower band (valence band) – 4 possible electrons in the upper band (conduction band) Energy Bands in Semiconductors Energy s The space The between the bands is the energy gap, or energy or forbidden band forbidden Insulators, Semiconductors, and Metals Insulators, s s s s This separation of the valence and conduction bands determines This the electrical properties of the material the Insulators have a large energy gap – electrons can’t jump from valence to conduction bands – no current flows Conductors (metals) have a very small (or nonexistent) energy gap – electrons easily jump to conduction bands due to thermal electrons excitation excitation – current flows easily Semiconductors have a moderate energy gap – only a few electrons can jump to the conduction band » leaving “holes” – only a little current can flow Insulators, Semiconductors,...
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This note was uploaded on 04/04/2010 for the course EE 3 taught by Professor Staff during the Winter '08 term at UCLA.

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