hw13 - d1 =10 17 /cm 3 , 1.1x10 17 /cm 3 , 10 18 /cm 3 ,...

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ECE 440 Homework XIII Fall 2005 Due: Friday, November 11, 2005 1. Field-effect transistors employ a mechanism different from that of BJT to control the output current by changing the charge density in the active region. The following problem is designed to illustrate the effect of changing charge density on the output current. Assume that a rectangular bar of silicon shown below consists of two layers, each of thickness t 1 and t 2 , respectively. The dimensions are D=100μm, W=4μm, t 2 =5μm and t 1 =200Å. The t 1 layer is uniformly doped with N d1 /cm 3 donors and N d2 =10 14 /cm 3 donors are also uniformly doped in the t 2 layer. A bias of 1 V is applied between x=0 and x=W. Determine the output current, I d , for different carrier densities in the t 1 layer. Specify the current for N
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Unformatted text preview: d1 =10 17 /cm 3 , 1.1x10 17 /cm 3 , 10 18 /cm 3 , and 1.01x10 18 /cm 3 . Also, estimate the Amplification Factor of this device for N d1 =10 17 /cm 3 and N d1 =10 18 /cm 3 . The Amplification Factor is defined as AF= ' I d / ' N d1 .For simplicity, use an average electron mobility of 1000 cm 2 /Vs for both layers and for various carrier densities to estimate the conductivity. 2. Redraw Figure 6-12 of band diagrams for the ideal MOS structure in an n-type silicon at (a) thermal equilibrium (b) electron accumulation (c) electron depletion and (d) strong inversion. Also, in the drawing show a simple circuit illustrating how the biasing is applied in each case. W t 2 t 1 D x=0 x=W...
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