HW5-solutions

# HW5-solutions - Georgia Institute of Technology School of...

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Georgia Institute of Technology School of Electrical and Computer Engineering ECE 3080: Semiconductor Devices Homework #5: Optoelectronic Devices 1. A silicon solar cell consists of an n-type emitter and a p-type base. The goal of this problem is to determine the optimum base doping in order to maximize efficiency. Assume that the generation rate is constant throughout the problem, and equal to the generation rate 150 µ m into the solar cell. You may assume that the saturation current is that of an ideal diode. The properties of the solar cell are shown below. N D = 1 × 10 19 cm -3 τ p = 0.1 µ sec D p = 0.5 cm²/sec x e = 2.5 µ m N A = ??? cm -3 τ n = ?? µ sec D n = 50 cm²/sec x b = 300 µ m (a) The incident power density is 90 mW/cm². Calculate the generation at 150 µ m, using an absorption coefficient of 100 cm -1 at a wavelength of 826.67 nm. S N = × = × × × × 2 2 cm photons eV photon J eV Ws J cm 0mW sec 10 75 . 3 82667 . 0 24 . 1 1 10 6 . 1 1 1 1 9 17 19 () ( ) 3 cm sec carriers × = × × × = α α = 18 4 17 10 37 . 8 10 150 100 exp 10 75 . 3 100 exp x N G S (b) The relationship between doping and lifetime is shown below. What is the optimum doping (to a factor of 10) for the solar cell, and for this doping, what is the short circuit current density, the open circuit voltage and the efficiency. You may assume that the FF = 0.79. Hint: you can eliminate at least one of the potential doping concentrations before you begin calculations.

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## This note was uploaded on 08/28/2010 for the course ECE 3080 taught by Professor Staff during the Fall '08 term at Georgia Tech.

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HW5-solutions - Georgia Institute of Technology School of...

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