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# hw12 - B assuming perfect emitter injection efficiency(c...

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ECE 440 Homework XII Fall 2005 Due: Wednesday, Nov 02, 2005 1. Redraw Fig. 7-3 for an n + -p-n transistor, and explain the various components of carrier flow and current directions. 2. Sketch the energy band diagram for an n-p-n transistor in equilibrium (all terminals grounded) and also under normal active bias (emitter junction forward biased, collector junction reverse biased). With the emitter terminal grounded, determine the signs (positive or negative) of the collector voltage V CE and base voltage V BE , relative to the emitter, that correspond to normal bias. 3. A symmetrical p + -n-p + Si bipolar transistor has the following properties: Emitter Base A = 10 -4 cm 2 N a = 2x10 17 /cm 3 N d = 10 15 /cm 3 W b =1 μm τ n = 0.1 μs τ p = 10 μs μ p = 180 cm 2 /V-s μ n = 1300 cm 2 /V-s μ n = 600 cm 2 /V-s μ p = 450 cm 2 /V-s (a) Determine if the straight-line approximation can be applied to evaluate the excess carriers in the base region. (b) With V EB = 0.3 V and V CB = - 4 V, calculate the base current I
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Unformatted text preview: B , assuming perfect emitter injection efficiency. (c) Calculate the emitter injection efficiency γ and the amplification factor β , assuming the emitter region is long compared to L n . 4. A Si p-n-p transistor has the following properties at room temperature: τ n = τ p =1 μs D n = D p =10 cm 2 /s A = cross-sectional area = 10-5 cm 2 N E =10 19 /cm 3 , N B =10 16 /cm 3 and N C =10 16 /cm 3 for emitter, base, and collector doping concentrations respectively. W E = 3 μm = emitter width W = metallurgical base width = 1.5 μm = distance between base-emitter junction and base-collector junction (a) Calculate the neutral base width W b for V CB = 0 and V EB = 0.3 V, repeat for 0.6V. (b) Calculate the base transport factor and the emitter injection efficiency for V EB = 0.3 and 0.6 V. (c) Calculate α , β ,I E , I B and I C for the two values of V EB ....
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