hw9_solutions - ECE 440 Homework IX Due Monday Fall 2008 1...

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ECE 440 Homework IX Fall 2008 Due: Monday, November 03, 2008 1. A p + -n silicon diode (V o = 0.956 volts) has a donor doping of 10 17 /cm 3 and an n- region width = 1 µm. Does it break down by avalanche or punchthrough? What if the doping is only 10 16 /cm 3 ? Refer to Fig. 5-22. Punchthrough occurs when the depletion region extends through the entire lightly doped region of the diode. (1) D br D A D A br n qN V V N N N N q V V x ) ( 2 ) ( ) ( 2 0 0 0 + + + = ε for N A >> N D From Figure 5-22 we see that V br for Si at N D = 10 17 cm -3 is about 12 volts. (2) m q x n μ 412 . 0 ) 10 ( ) 956 . 12 ( 2 17 0 = Since this is smaller than the physical length of the n-region the diode will break down via avalanche breakdown first. However, when N D =10 16 cm -3 , V br is around 60 volts. (3) m q x n 82 . 2 ) 10 ( ) 956 . 60 ( 2 16 0 = This is larger than the physical length of the n-region so punchthrough will occur before avalanche breakdown. 2.
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hw9_solutions - ECE 440 Homework IX Due Monday Fall 2008 1...

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