Epitaxial growth of very large grain bicrystalline Cu(In,Ga)Se2 thin films by a hybrid sputtering method

Abstract

Epitaxial bicrystals of Cu(In,Ga)Se2 (CIGS) have been grown and characterized spanning high angle incoherent grain boundaries. The grain boundaries in the CIGS were generally found to be fully dense, although voids were occasionally observed as is typical in CIGS polycrystals. There was no significant difference in composition of the grains across the boundary. No reduction in dislocation density near the grain boundary was found. X-ray diffraction results were consistent with partially strained epitaxial layers with domains tilted relative to the surface normal and with different rotations in the surface plane. The tetragonal symmetry of the unit cell appears to have affected the residual strain in the layers and the amount of misfit observed. The surface morphology was found to reflect trends observed in growth of single well-oriented crystals. Differences in surface potential of air-exposed grains showed a morphology-dependent work function. However, no significant potential difference was observed that was related to the grain boundary. Surface morphology effects were much greater. The surface showed a clear rotation of morphology across twin boundaries in the surface plane of one grain. The twin boundaries were also fully dense.