Compositional inhomogeneities in type-I and type-II superlattices for GaAsSbN-based solar cells: Effect of thermal annealing

Structures based on GaAs(Sb)(N) semiconductor alloys for high efficiency multi-junction solar cells

“…Figure 6.6 a) shows LAADF images of SL-II 12 sample as-grown and RTA. The N-containing layers are easily identified since they present a much brighter contrast than the GaAs 1-x Sb x layers (see Section 3.2.5) [182,210]. Abrupt interfaces with symmetrical and squared N profiles along the growth direction can be seen in both samples, which points to a very low segregation of N outside the GaAs 1-y N y layers even after the RTA.…”

“…In the case of dilute nitride GaAs-based alloys, it is the big difference in the atomic radius of the As and N atoms which causes high enough local distortions in the material lattice to dominate the LAADF imaging contrast over the Z-contrast [180,181]. Therefore, in this kind of STEM image mode N-rich regions appears with bright contrast than the GaAs [180,181] or even the GaAs 1-x Sb x regions [177,182], the contrast level depending on the Sb concentration.…”

“…Both the number of clusters and the cluster's total area are doubled in the as-grown sample as compared to the RTA one (36 versus 18 and 120 nm 2 versus 50 nm 2 , respectively). [182].…”

“…Nevertheless, to the best of our knowledge, different type-II GaAs 1-x Sb x /GaAs 1-y N y strain-balanced SL structures with elevated number of periods have been grown by MBE and systematically analyzed for the first time during this Thesis. This Chapter is based on results presented in articles [182,[209][210][211] with permission of the corresponding journals.…”

“…In this series, as-grown solar cells have shown hindered solar cell performance caused by the relatively "high" N content. The first part of this Chapter is based on the articles [182,220], the second is still unpublished.…”