OBIC studies

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