Advances in III-V

The use of compositionally graded SiGe buffers to bridge material mismatches between GaAs based III-V compounds and Si substrates has shown extreme promise as the means by which high efficiency III-V solar cells can be integrated with low-cost Si substrates. In this paper, we describe recent progress in three areas that are critical to realize the potential of GaAs/Ge/SiGe/Si integration for photovoltaic technologies of the future. First, we show that p+n configured GaAs cells are much less sensitive to dislocation-related degradation than n+p configured cells, indicating a preferred polarity for heteroepitaxial III-V solar cells. Second, by correlating direct, microscopic observation using cross sectional TEM and EBIC with sub-GaAs bandgap light I-V studies, we show that interface states present at the GaAs/Ge interface unrelated to anti-phase domains are responsible for uncontrolled sub-GaAs bandgap PV response for p+n cells. Further, we demonstrate a solution to this problem that completely eliminates and reproducibly controls such interfacial activity. Finally, GaAs/Ge/SiGe/Si cell areas are increased from 0.36 cm2 to 4 cm2 without reduction of cell performance, the first experimental evidence that no fundamental limitations are evident for scaling III-V/Ge/SiGe/Si cells to large areas. 1