Optimization of concentrator GaAs photovoltaic devices with InAs quantum dots through substrate misorientation and electroplating

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Title: Optimization of concentrator GaAs photovoltaic devices with InAs quantum dots through substrate misorientation and electroplating
Author: Mackos, Chelsea
Abstract: Optimization of InAs critical coverage is important to realizing controlled growth in quantum dot devices. Substrate misorientation can change the value of critical coverage but also creates more uniform quantum dots in both size and distribution. Uniform quantum dots are advantageous in concentrator photovoltaic devices due to increases in sub bandgap response. Concentration photovoltaic devices are designed to compete on a cost per watt basis with other terrestrial photovoltaic devices. This benefit can only be utilized if the fabrication process is also cost effective. Concentration devices rely on dense thick Au grid finger design to reduce series resistance, which can add to processing costs. This work explores GaAs p-i-n photovoltaic devices grown via organometallic vapor phase epitaxy with InAs quantum dots using the Stranski-Krastanov growth method on substrates misoriented 6° off (100) in the [110] direction and 2°off (100) in the [110] direction. Both preliminary test and devices structures were created in order to study device performance through external quantum efficiency, and current-voltage behavior, as well as material properties through atomic force microcopy and photoluminescence. Results of this work show that 2° [110] sample results in lower critical coverage as compared to the 6° [110] (approximately 1.8 ML verses approximately 2.1 ML). The 6° [110] substrate also showed a more uniform density and size distribution of QDs. In addition, the standard electroplating process was evaluated and improved for better metal adhesion and safer lab practices. Metal adhesion was improved and safer lab practices were implemented. Finally, concentration devices were fabricated using the new electroplating process and tested up to 600 suns at the NASA Glenn Research Center. These results are important to realizing the full benefits of QD structures such as increased optical absorption. Results show the baseline devices performed to the designed specification while more investigation in needed within the QD samples in order to evaluate the cause of increased internal series resistance.
Record URI: http://hdl.handle.net/1850/15070
Date: 2011-12

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