Assessment of MOCVD- and MBE-grown GaAs for high-efficiency solar cell applications

A critical assessment of the photovoltaic quality of epitaxial GaAs grown by metal-organic chemical vapor deposition (MOCVD) and by molecular-beam epitaxy (MBE) is reported. Epitaxial films of nominally identical structure were grown by the two techniques and were fabricated into p-n heteroface solar cells. The 0.5-cm by 0.5-cm cells were then characterized and compared. The MOCVD-grown films produced independently verified record efficiency cells of 24.8 percent under 1-sun AM1.5 global conditions while the MBE-grown films produced similarly high efficiencies of 23.8 percent. The material qualities of the two films in terms of minority-carrier diffusion lengths and surface recombination velocities were quite comparable. These results demonstrate that the quality of MBE-grown films can be quite comparable to the best MOCVD-grown films and that they are suitable for high-efficiency solar cells. (I.E.)