figs06

figs06 - F IGURES FOR C HAPTER 6 Figure 6-1 Lattice...

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Unformatted text preview: F IGURES FOR C HAPTER 6 Figure 6-1 Lattice structure and energy levels of silicon. (a) schematic planar crystal arrangement with thermal breakup of one valent bond resulting in a hole and a moving electron for T > 0°K. (b) equivalent energy band level representation whereby a hole is created in the valence band W V and an electron is produced in the conduction band W C . The energy gap between both bands is indicated by W g . Si Si Si Si Si Si Free electron Hole Hole Valence band Conduction band Forbidden Band or Bandgap W C W V W g (a) Planar representation of covalent bonds (b) Energy band levels Electron energy Table 6-1 Effective concentrations and effective mass values at T = 300°K Semiconductor Silicon (Si) 1.08 0.56 2.8 × 10 19 1.04 × 10 19 1.45× 10 10 Germanium (Ge) 0.55 0.37 1.04 × 10 19 6.0 × 10 18 2.4 × 10 13 Gallium Arsenide (GaAs) 0.067 0.48 4.7 × 10 17 7.0 × 10 18 1.79× 10 6 m n * m ∕ m p * m ∕ N C cm 3 – ( 29 N V (cm 3 – 29 n i (cm 3 – 29 Figure 6-2 Conductivity of Si, Ge, GaAs in the range from –50°C to 250°C. 10 10 –2 –50 50 100 150 200 250 Temperature, C o Conductivity, cm σΩ Ge Si GaAs 10 2 10 –4 10 –6 10 –8 10 –10 10 –12 10 –14 –1 –1 (a) Intrinsic (b) n- type (c) p-type Figure 6-3 Lattice structure and energy band model for (a) intrinsic, (b) n-type, and (c) p-type semiconductors at no thermal energy. W D and W A are donor and acceptor energy levels. Valence band Conduction band W C W V W F Valence band Conduction band W C W V W F W D Valence band Conduction band W C W V W F W A Si Si Si Si Si Si Si Si Si Si P Si Si Si Si Si Si Si Si B Si Si Si Si Si Si Si Figure 6-4 Current flow in the pn-junction p- type n- type Space charge Space charge x x = 0 Electric field Hole diffusion current Electron diffusion current I F (a) pn-junction with space charge extent (b) Acceptor and donor concentrations (c) Polarity of charge density distribution (d) Electric field distribution Figure 6-5 The pn-junction with abrupt charge carrier transition in the absence of an externally applied voltage. p-type n-type Space charge Space charge x x = 0 –d p d n p = N p A (majority carrier) n = N n D (majority carrier) x –d p d n n, p n << p p p p << n n n x –qN A qN D d n d p ρ ( x ) x E –d p d n E = –qN d /( ) A p r ε ε (e) Barrier voltage distribution Figure 6-5 The pn-junction with abrupt charge carrier transition in the absence of an externally applied voltage. (Continued) x V diff –d p d n V ( x ) Figure 6-6 External voltage applied to the pn-junction in reverse and forward directions. V A x V diff V V A x V d n d n –d p –d p Voltage distribution in the pn- junction (a) Reverse biasing ( V A < 0) (b) Forward biasing ( V A > 0) E x E x p n p n Space charge distribution in the pn-junction Electric field distribution in the pn-junction Figure 6-7 The pn-junction capacitance as a function of applied voltage....
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This note was uploaded on 01/31/2012 for the course EE 4002 taught by Professor Scalzo during the Fall '06 term at LSU.

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figs06 - F IGURES FOR C HAPTER 6 Figure 6-1 Lattice...

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