OBIC studies: Classification of structural defects and their influence on the performance of MOCVD grown GaAs solar cells

By means of the OBIC (optical beam induced current) technique, where a focused laser spot of about 6 μm in diameter is used in combination with a computer-controlled translation mechanism and data acquisition system, the spatially resolved structural behavior of metalorganic chemical vapor deposition (MOCVD)-grown GaAs solar cells was studied. The overall performance of the cells was studied as a function of the difference in the GaAs substrate and the MOCVD growth conditions. A classification has been made for typical defects that either originated from the substrate or were created during the MOCVD growth. The study of the oval defects in the grown layers was emphasized. It was found that ovals with a polycrystalline center have a strong effect on the local response, as was expected from the short diffusion length of the minority carriers. Some oval defects have a region around them in which the OBIC response is improved compared with the defect-free surface, indicating a locally better solar cell performance