Solar cells based on III-V semiconductors are the world's most efficient, but their use is currently limited to applications such as space power because of their high cost. Post-growth device processing, which includes metallizing the solar cells and isolating the active areas, makes up a significant portion of fabrication cost. Mesa isolation is typically done by masking active areas with polymer-based photolithography and chemically etching the surrounding epitaxial layers to electrically isolate the solar cells from, for example, flaws in the epitaxy on the edge of the wafer, or from each other. In this work, we use a femtosecond laser micromachining system to mesa-isolate GaAs and GaInP solar cells, two common subcell materials in multijunction III-V devices, as an alternative to photolithography and etching. We demonstrate GaAs solar cells mesa isolated with laser ablation with a performance similar to that of a baseline, but a significant degradation of performance for GaInP solar cells. We will discuss the damage we observe from laser ablation of these materials, including an Auger electron spectroscopy analysis of the ablated regions.
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