PECVD grown DBR for microcavity OLED sensor
Bohlen, Brandon (2007) PECVD grown DBR for microcavity OLED sensor. Masters thesis, Iowa State University.
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Organic light emitting devices (OLED) have become a popular topic of research and product development in the past decade. The use of OLEDs as the light source in a compact photoluminescent sensor has been studied for the detection of various chemicals. Controlling the bandwidth of light emitted by the OLED would be beneficial to the sensitivity of these sensors. By building the OLEDs in a microcavity structure, the bandwidth and peak frequency of light being emitted can be controlled and adjusted to a specific value. A key component of a microcavity is a partially transmitting reflector: a reflector with less than 90\% reflectance. A dielectric mirror can be manufactured with varying reflectance and can be well integrated into the OLED manufacturing process. The dielectric mirror created for this project is a distributed Bragg reflector (DBR) made of alternating silicon nitride and silicon dioxide layers. The layers were grown with plasma-enhanced chemical vapor deposition (PECVD); a low temperature, low pressure deposition system. Building a DBR using PECVD allows for the creation of the reflector on any surface that can withstand temperatures of approximately 300C and takes less than an hour to make up to four mirrors. The growth rate of silicon nitride and silicon dioxide films from plasma enhanced chemical vapor deposition of silane, ammonia, and nitrous oxide was characterized. The PECVD system has no growth rate measurement capabilities, therefore characterization was the only way to determine the ultimate growth parameters for this project. A reapeatable method for the manufacture of silicon dioxide/nitride distributed Bragg reflectors for use in microcavity OLED sensors was designed. Three DBRs were grown on glass slides and measured with a spectrophotometer. The three slides had reflectance of between 75% and 85% with full widths at half maximum of 170-180nm centered around 570-590nm.
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