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ece340Spring04HW11Sol

# ece340Spring04HW11Sol - ECE 340 1 Homework IX Due Friday...

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ECE 340 Homework IX Spring 2004 Due: Friday, March 19, 2004 1. A n + -p Si junction with a long p-region has the following properties: N a =1.5x10 16 /cm 3 ; μ n = 1020 cm 2 /V-s; μ p = 380 cm 2 /V-s; τ n =1 μs. If we apply 0.7 V forward bias to the junction at 300 K, what is the electric field in the p-region far from the junction? Draw a band diagram in the p-region far from the junction assuming that the junction is at x=0 and the p-side is in x>0. Solutions: 2 43 1.5 10 i p p n nc m p == × , 2 / 0.0259 1020 26.42 / nn Dk T q c m s µ × = 6 26.42 10 0.00514 n L cm = since it’s an n + -p Si junction, / 19 0.7/0.0259 2 26.42 ( 1) 1.6 10 15000 ( 1) 6.74 / 0.00514 qV kT n p n D Jq ne e A c m L =− = × ×× = Far away from junction, the diffusion current goes to zero, the current composed of drift current: () ( 0 ) drift p pa Jx J q N =∞ = = = = Ε 19 16 6.74 7.39 / 1.6 10 380 1.5 10 Vc m Ε= = × × , E is toward –x direction since p is on x>0 Band diagram: 2. Consider the following Si p-n junctions operating at 300 K. (a) Using Eq. (5-8), calculate the contact potential V o for N a = 5x10 14 and 5x10 18 /cm 3 , with N d = 10 15 , 10 17 , 10 19 /cm 3

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ece340Spring04HW11Sol - ECE 340 1 Homework IX Due Friday...

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