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Unformatted text preview: 1 ECE 3150 Homework 1 Due 2/5/2009 by 10:30 AM 1. (Atomic doping) For a piece of homogeneous silicon under equilibrium at room temperature with n i =1.02 10 10 cm-3 , find the electron and hole concentrations where both types of exist: N A =10 18 cm-3 and N D =10 15 cm-3 : (a) Use the charge neutrality condition and np=n i 2 to obtain the exact solution of n and p (4 pts) (b) Explain why p = N A N D is a good approximation for the majority carrier here (4 pts) (c) Repeat (a) and (b) for N A =10 18 cm-3 and N D =10 17 cm-3 . (4 pts) (d) If you are asked to calculate the electrostatic potential for the case in (c), should you use p or N A ? What is the potential using the intrinsic level as reference? (4 pts) (e) If we build a resistor with this semiconductor, how will you compare the mobility for the compensational doping with both N A =10 18 cm-3 and N D =10 17 cm-3 and the mobility for the case with only N A =9 10 17 cm-3 ? Briefly explain. (4 pts) 2. (Carrier concentration in different temperatures) The intrinsic silicon has E gap = 1.1eV and n i = 1.02...
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