Ideal GaP/Si heterostructures grown by MOCVD: III-V/active-Si subcells, multijuntions, and MBE-to-MOCVD III-V/Si interface science

Abstract

High-quality, heterovalent nucleation of defect-free epitaxial GaP on (100)-oriented Si substrates is an enabling accomplishment toward a pathway for the creation of III-V/Si multijunction photovoltaic devices in which the Si growth substrate can simultaneously act as a near-ideal sub-cell through a monolithic metamorphic GaInP/GaAsP/Si structure. While recent efforts have achieved this goal via molecular beam epitaxy (MBE), the science developed in those efforts is fundamental to the GaP/Si interface. Here this knowledge is utilized to achieve the successful transition from MBE to an all-MOCVD (metal-organic chemical vapor deposition) process, in which all nucleation-related defects are simultaneously and totally avoided for ideal GaP/Si interfaces and subsequent metamorphic III-V materials. Four main topics are presented: (1) GaP/Si(100) grown by MOCVD free of antiphase domains and stacking defects; (2) growth, fabrication, and testing of GaP/active-Si sub-cells; (3) MOCVD/MBE-grown GaAsP/active-Si multijunction structures and component cells having target lattice constants and bandgaps for high efficiency dual and triple junction cells, and (4) comparative interface studies of MBE- and MOCVD-grown III-V/GaP/Si cell architectures.