Antiphase disorder in GaAs/Ge heterostructures for solar cells

Antiphase disorder in metal organic vapour phase epitaxy grown GaAs/(100)Ge heterostructures has been studied both in as-grown materials and in GaAs s olar cells by chemical etching, transmission electron microscopy, and catho doluminescence. All the samples are single domains at the surface due to the self-annihilat ion of antiphase domains whose size decreases as the misorientation angle i ncreases. Completely antiphase domain-free epitaxy has been achieved for su bstrate miscuts greater than 3 degrees off towards [111]. A reversal in sublattice location has been found in the GaAs layers varying the misorientation angle and the growth temperature. A model to explain th is result has been proposed based on the role of surface steps in the nucle ation process. Strong interaction between antiphase boundaries and misfit dislocations has been found in all the heterostructures. In solar cells antiphase domains have been observed in high densities in th e initial layer of GaAs deposited on Ge. The successful realisation of high efficiency solar cells is due to the overgrowth of these domains by single phase material over most of the wafer area. (C) 2000 Elsevier Science Ltd. All rights reserved.