Nitrogen incorporation in GaInNAs grown by chemical beam epitaxy for multi-junction tandem solar cell

GaInNAs films for the ultra high-efficiency (>40%) 4-junction tandem space solar cells ((Al)GaInP/GaAs/ GaInNAs/Ge) have been grown by using chemical beam epitaxy (CBE) in this study. In the growth of GaInNAs films, the selection of nitrogen source and understanding of nitrogen incorporation is important because nitrogen is play an important role in the crystallization and electrical properties of III-V-N compound materials. A proper nitrogen source between monomethylhydrazine (MMHy) and dimethylhydrazine (DMHy) was investigated, and the nitrogen incorporation in samples grown with MMHy was higher. From the dependence of nitrogen concentration on the substrate temperature, three distinct regions were observed, even in the nitrogen concentration usually decreased with increasing the substrate temperature, and a low FWHM value was obtained at an intermediate temperature. In addition, the dependence of the nitrogen incorporation on the ratio of N/(N+As) was investigated, and at a low temperature, the nitrogen concentration increased with increasing the ratio of N/(N+As). From these results, the nitrogen incorporation in GaInNAs films grown with the substrate temperature and the ratio of N/V elements in CBE technique is clarified, and the relationships between the nitrogen incorporation and crystallization of GaInNAs are clear.