IMPROVING THE MATERIAL QUALITY OF MOVPE GROWN (GaIn)(NAs)

摘要

The diluted nitride (GaIn)(NAs) material system grown lattice matched to GaAs or Ge with a 1 eV bandgap is an interesting material for the use in multi-junction solar cells. By inserting a solar cell made of (GaIn)(NAs) as a fourth junction into the well developed 3-junction solar cell consisting of (GaIn)P/(GaIn)As/Ge significant efficiency improvements can be expected. However, up to now the introduction of nitrogen into (GaIn)As tended to degrade the material quality resulting in low diffusion lengths. Still it is not clear whether this is due to extrinsic, growth related defects or an intrinsic property of the material. This study discusses up to which extent optimised growth and annealing conditions can be found to circumvent these properties of the material and hence improve device performance. First results of solar cell structures with optimised annealing conditions are presented and discussed in the light of structural changes observed in the quaternary alloy upon annealing.