22.SSD (EE-2080)_Lect22_7march

22.SSD (EE-2080)_Lect22_7march - SSD(EE-2080) Lecture 22...

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Unformatted text preview: SSD(EE-2080) Lecture 22 Dr. Shiv Govind Singh sgsingh@iith.ac.in Assistant Professor Electrical Engineering Semester 2, Y-2010/11 Reference Text Book: 1. Physics of Semiconductor Devices, S. M. Sze , John Wiley & Sons (1981). 2. Solid State Electronics by Ben G. Streetman and Sanjay Banerjee , Prentice Hall International , Inc. 3. Semiconductor Physics and Devices, Donald A. Neamen, Tata Mcgraw- Hill Publishing company Limited. Reference Book: • 1. The PN Junction Diode: Volume II (2nd Edition) (Modular Series on Solid State Dev., Vol 2) George W Neudec Four step to draw a Band Diagram N d N a Four step to draw a Band Diagram N d N a E f χ 1 χ 2 Vacuum level E c Built ‐ in Potential: boundary conditions @ infinity E f χ 1 χ 2 E c V bi V n V p V bi + χ 1 + d 1 = χ 2 +E g- d 2 V bi = E g + χ 2- χ 1 -v p-v n qV bi =kTln(N c N v /n i 2 +kTln(N a /N v )+kTln(N d /N c ) Hence, V bi =(kT/q)ln(N a N d /n i 2 ) If material is same both side of junction E g =kTln(N c N v /n i 2 ) qV p =-kTln(N a /N v ) qV n =-kTln(N d /N c ) • V bi for Si 0.6 to 0.8 V Important consequences As we change the voltage across the p-n junction depletion with changes , so we can think of capacitance effect. Calculate Vbi for p-n junction consider Ge p-n junction at room temperature. Depletion width V bi Electric filed dE/dx=ρ/ε s For p-type side dE/dx=-qN a /ε s E=-(qN a /ε s )(x+x p ) E=-(qN d /ε s )(x-x n ) qN a /ε...
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22.SSD (EE-2080)_Lect22_7march - SSD(EE-2080) Lecture 22...

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