Control of Nitrogen Inhomogeneities in Type-I and Type-II GaAsSbN Superlattices for Solar Cell Devices

Abstract

Superlattice structures (SLs) with type-II (GaAsSb/GaAsN) and -I (GaAsSbN/GaAs) band alignments have received a great deal of attention for multijunction solar cell (MJSC) applications, as they present a strongly intensified luminescence and a significant external quantum efficiency (EQE), with respect to the GaAsSbN bulk layers. Despite the difficulties in characterizing the distribution of N in dilute III-V nitride alloys, in this work we have obtained N-compositional mappings before and after rapid thermal annealing (RTA) in both types of structures, by using a recent methodology based on the treatment of different scanning transmission electron microscopy (STEM) imaging configurations. Texture analysis by gray level co-occurrence matrixes (GLCM) and the measurement of the degree of clustering are used to compare and evaluate the compositional inhomogeneities of N. Comparison with the Sb maps shows that there is no spatial correlation between the N and Sb distributions. Our results reveal that a better homogeneity of N is obtained in type-I SLs, but at the expense of a higher tendency of Sb agglomeration, and the opposite occurs in type-II SLs. The RTA treatments improve the uniformity of N and Sb in both designs, with the annealed sample of type-II SLs being the most balanced structure for MJSCs.

Analysis of Current Transport Mechanism in AP-MOVPE Grown GaAsN p-i-n Solar Cell

“…The GaAsN signal located on the right side is asymmetrically broadened which might suggest inhomogeneous nitrogen distribution in GaAsN layer. Composition fluctuations in dilute nitride layers such as GaAsN or InGaAsN are well known [16,[50][51][52]. Nitrogen has a tendency to form clusters, which, together with N-related defects (for instance, (N-N) As , (N-As) As [5,35]), contribute to the formation of non-radiative recombination centers [30] and carrier localization effects [53].…”

Growth interruption strategies for interface optimization in GaAsSb/GaAsN type-II superlattices

“…Recently, type II GaAsSb/GaAsN superlattices (SLs) have been proposed as a suitable structure to form such a 1.0-1.15 eV sub-cell, that would allow their implementation in the optimal design of GaAs lattice-matched multijunction solar cells [4,5]. Here, the authors suggest that this strategy optimizes control over the composition distribution of the different elements concerning bulk GaAsSbN counterparts, reducing the growing problems associated with concomitant Sb and N incorporation [6,7]. However, atomic-scale compositional analyses by electron microscopy in this type of SLs revealed that while the N distribution is spatially confined in the GaAsN layers, the same is not true for that of GaAsSb layers, there is a significant Sb segregation affecting both interfaces [8].…”

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

“…Moreover, in the quaternary GaAs 1-x-y Sb x N y regions, the simultaneous presence of Sb also hinders the N characterization [177]. However, a new methodology proposed in [177,178] to detect and quantify N presence through ADF imaging has been employed on some samples of this Thesis. The scattered intensity in HAADF conditions is especially sensitive to high Z-number atoms (which is known as Z-contrast) [179].…”