GaAs Sliver solar cells for linear microconcentrator applications

Gallium arsenide (GaAs) solar cells have shown demonstrated efficiencies of over 29% and are highly regarded in terms of stability, durability and performance. In order to make use of this excellent solar material while reducing inherent material costs, concentration of sunlight can be utilized. A linear microconcentrator has been designed to provide ∼7x concentrated sunlight to a narrow, long, GaAs cell, with a large area silicon cell underneath to collect the sub-bandgap light passing through the GaAs as well as any diffuse light that is not focused by the concentrator. This tandem linear microconcentrator module has demonstrated potential for efficiencies > 30%. In order to further optimize the design of the GaAs cell, a technique is being developed based on the Sliver method previously used with silicon. In order to adapt the Sliver process for GaAs applications it is critical to develop a technique for etching high aspect ratio grooves in GaAs. This work details the use of ICP/RIE to etch extremely deep, high aspect ratio grooves in GaAs up to a depth of $120 \mu \mathrm{m}$ with an aspect ratio of 9. The pathway for developing the etched GaAs into solar cells via ALD deposition of passivating contacts is also discussed.