Background: With an efficiency surpassing silicon solar cells utilizing gallium arsenide (GaAs) have helped power satellites and Mars rovers. This class of high performance photovoltaics requires that thin layers of the compound be precisely grown and doped with carbon for use as semiconductors. Growing doped GaAs economically and with controlled thickness is increasingly vital to the solar industry. The most common method is metal-organic vapor phase epitaxy (MOVPE) which uses expensive and toxic materials. Enabling ultrathin layering MOVPE currently is favored over an older faster but traditionally less precise method. The older method called hydride vapor phase epitaxy (HVPE) is worthy of being revisited to address its precision problems. Technology Description: UW–Madison researchers have developed a new method for growing layers of carbon-doped GaAs using a haloalkane dopant and HVPE. First a substrate is exposed to a gas mixture composed of gallium arsenic and a haloalkane dopant. Conditions in the reactor including gas flow rate growth temperature and timing are controlled to grow layers of carbon-doped GaAs on the substrate via HVPE and are adjustable to maximize dopant concentrations. The process may be repeated to deposit additional layers. Also a variety of haloalkanes based on bromine chlorine and iodine can act as dopant. Using the new method the concentration of carbon within the layer can be monitored and altered as needed. Applications: 1) pn junctions for high quality solar cells 2) Satellite photovoltaics 3) Heterojunction bipolar transistors 4) Semiconductor laser diodes Opportunity for collaboration: The Wisconsin Alumni Research Foundation (WARF) is seeking commercial partners interested in developing an improved method for growing crystalline layers of carbon-doped gallium arsenide via hydride vapor phase epitaxy.
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