Development of Low-TDD GaAsyP1-y/GaP/Si Metamorphic Materials for High-Efficiency III-V/Si Photovoltaics

Abstract

Metamorphic III-V/Si materials with low threading dislocation density (TDD) are critical to realizing high-efficiency III-V/Si multijunction photovoltaics. In pursuit of a dual junction III-V/Si design with a GaAs0.75P0.25 top junction epitaxially integrated on a Si bottom junction, we report on progress made in the development of GaP/Si and GaAsyPl-y/Si materials with significantly reduced TDD. Using a tightly integrated study of fundamental dislocation dynamics, rapid electron microscopy based feedback on dislocation populations, and MOCVD process development, we have fully re-engineered the GaP on Si growth process. Our new approach results in a TDD of 7x104 cm−2 for 50 nm thick films. Implementation of a novel dislocation glide enhancing heterostructure then enabled subsequent growth of fully-relaxed, 500 nm total thickness n-GaP with a TDD of 2.4×106 cm−2. When applied to the production of full GaAs0.75P0.25/Si tandem solar cell structures, but without any significant optimization thus far, this low TDD is effectively maintained, yielding a terminal TDD of only 3.0x106 cm−2, sufficient to support high photovoltaic performance.