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Unformatted text preview: 11/9/11 1 Chapter 18 - 35 SEMICONDUCTORS TWO TYPES: INTRINSIC and EXTRINSIC Chapter 18 - 36 Intrinsic Semiconductors I Pure material semiconductors: e.g., Silicon & Germanium: Group IVA materials I Compound semiconductors: III-V compounds I e.g.: GaAs & InSb II-VI compounds I e.g.: CdS & ZnTe The wider the electronegativity difference between the elements the wider the energy gap 11/9/11 2 Chapter 18 - 37 Pure Semiconductors: Conductivity vs. T I .A. 3<? pure Silicon: increases with T opposite to metals Adapted from Fig. 19.15, Callister 5e . (Fig. 19.15 adapted from G.L. Pearson and J. Bardeen, Phys. Rev. 75 , p. 865, 1949.) Electrical Conductivity, (Ohm-m)-1 50 100 1000 10-2 10-1 10 10 1 10 2 10 3 10 4 pure (undoped) T (K) electrons can cross band gap at higher T Material Si Ge GaP CdS Band gap (eV) 1.11 0.67 2.25 2.40 Selected values from Table 18.3, Callister & Rethwisch 8e . kT / E gap ! " # e undoped Energy filled band filled valence band empty band filled states GAP ? Chapter 18 - 38 Conduction in Terms of Electron and Hole Migration Adapted from Fig. 18.11, Callister & Rethwisch 8e ....
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This note was uploaded on 12/16/2011 for the course ENGR 220 taught by Professor Barsoum during the Spring '08 term at Drexel.
- Spring '08