Development of recessed contacts for mechanical stacking of GaSb solar cells

摘要

Transfer printing is a formidable technique to stack multijunction solar cells while avoiding existing epitaxial limitations. Thus, a larger portion of the solar spectrum can be harvested through careful design optimization. In this process, metal contacts are embedded within a highly conductive lateral conduction layer (LCL) on the lower subcells. A readily available low bandgap candidate for a multijunction stack includes a GaSb solar cell with a 1.0 eV Al0.2Ga0.8Sb LCL. Processing of a bare AlGaSb layer is difficult, as standard photolithography processes and wet etch chemistries leave the surface excessively roughened and inhibit good ohmic contact. Several dry etch recipes are investigated to etch the AlGaSb LCL while leaving a smooth surface. A recipe based on a gas mixture of BCl3/Ar was determined to be a viable candidate for dry etching of AlGaSb and used to fabricate a GaSb solar cell with recessed contacts in an AlGaSb LCL.