Solar system question
Question Description
1. An LED manufacturing company is producing radiation emitting sources at the following specific wavelength bands: (1) 0.44 to 0.46 μm, (2) 0.58 to 0.62 μm, and (3) 0.78 to 0.82 μm. Consider you are designing a photo-detector for this company using a high-quality silicon crystal with an active area 1 cm x 1cm having a thickness of 100 μm. This photo-detector will be used to measure the power density of radiation received from each light source in mW/cm2. Testing will be done with only one bulb at a time on wavelengths centered at (1) 0.45, (2) 0.6 and (3) 0.8 μm. The photodetector will be located 500 cm from the light source.
The photo-detector will be housed inside a glass case to protect it from environmental degradation. The glass window on top of the detector causes 8% loss due to reflection in each case; the front surface of the detector does not have any anti-reflection coating (ARC).
Your objective is to maximize the sensitivity of the detector so that the difference in current under the illuminated and under the dark conditions is highest at normal incidence. You can dope the silicon crystal if needed. The current is measured by attaching two electrodes across the Si crystal detector on the two opposite sides (active surface area is 1 cm2) and by applying 5 V and using a sensitive current meter in series.
(a)If you are doping the crystal, explain the advantages of making it p- or n-type. What dopant concentration would you use?
(b)Calculate the current under dark conditions; explain the steps you are taking
(c)Calculate the reflection losses in each case (For optical properties of silicon, use the website http://www.pveducation.org/pvcdrom/materials/optical-properties-of-silicon)
(d)Calculate the absorption of radiation in each case by the crystal (See the absorption coefficients of silicon at the PVCDROM website
(e)Calculate the current under the three illuminated conditions at the three wavelengths at 300K, explain the steps in your calculations.
2.
Consider the company finds the detector you designed and constructed works very
satisfactorily. They now want to use it to measure and monitor sun hours at
different prospective locations for PV Module installations.
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