In-situ smoothing of facets on spalled GaAs(100) substrates during OMPVE growth of III-V solar cells

This presentation describes how faceted GaAs(100) surfaces can be flattened during organometallic vapor-phase epitaxy (OMVPE) growth, by systematically examining results for different material/dopant combinations. This work is motivated by the use of spalling for substrate removal and reuse, as a pathway toward reducing the cost of III-V solar cells. Here we consider the growth of III-V cells on spalled GaAs(100) substrates, which typically have facetted surfaces after spalling. To facilitate the growth of high-quality cells, these facetted surfaces should be smoothed prior to cell growth. This study presents results on the OMVPE growth of surface-smoothing buffer layers prior to cell growth, and finds that the material/dopant combination used for smoothing must be carefully chosen for a good outcome. Some material/dopant combinations (i.e. C:GaAs) smooth the surface quite quickly, but others (i.e. Zn:GaAs) can significantly roughen it. Here we provide a systematic study based upon representative cases, and discuss the impact of these material/dopant combinations on surface smoothing and subsequent cell growth. Representative examples will be presented, along with a discussion of the underlying growth processes.