Properties and structure of antiphase boundaries in GaAs/Ge solar cells

Antiphase boundaries (APBs) are particularly crystallographically simple but technologically troublesome boundaries that tend to occur in profusion in GaAs grown epitaxially on (100) oriented substrates of Ge or Si. APBs were found to form only in a narrow band near the periphery of square wafers of GaAs/Ge grown by metal organic chemical vapour deposition (MOCVD) to make solar cells for use on space satellites. Bands of APBs have continued to appear in a fraction of the wafers grown over a period of several years. The geometry of these bands is presented and the distribution and structure of the APBs within it was studied by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) electron beam induced current (EBIC) and cathodoluminesence (CL). TEM showed that APBs and misfit dislocations were present in the bands in earlier specimens while stacking faults were the only defects in areas outside the bands in more recent specimens. The significance of the formation of APBs only in a limited area and of their relatively large interface recombination velocities are discussed.