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Unformatted text preview: ECE 3040 Homework 3 The goal of this homework is to design a photocell (also known as a photoelectric cell or photoelectric resistor) that will respond to light and change its resistance. This device may be used in a later homework problem. The photocell is basically nothing more than a resistor made out of semiconductor material and is typically arranged in a package as a long skinny slither of very thin semiconductor, most often CdS due to its near optimal bandgap for absorbing the solar spectrum and relative inexpensive material. While a real device has a long serpentine shape (see below) we will simply use a rectangular block as was done in class. The working specifications of your design are for a resistance of 1 Giga-ohm in dark and 3 Mega-ohms in bright light (Intensity, I o =60mW/cm 2 ). Given : The CdS material is p-type with Na=1e14 cm-3 and n i =2e6 cm-3 The mobilities are μ n =100 cm 2 /V-sec and μ p =500cm 2 /V-sec; Note: For this problem it is okay to assume low level injection and thus valid to use the formula:...
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This note was uploaded on 02/17/2010 for the course ECE 3040 taught by Professor Hamblen during the Spring '07 term at Georgia Institute of Technology.
- Spring '07