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We examine the arsenic distribution and its influence on dopant activation in poly-crystalline CdTe1−xSex solar cell absorbers prepared by vapor transport deposition followed by CdCl2 annealing. For as-deposited CdTe:As, local-electrode atom probe (LEAP) tomography reveals non-uniform distributions of arsenic clusters in the top “doped” layers. Following CdCl2 annealing, secondary ion mass spectrometry suggests that arsenic has diffused into the entire CdTe layer, while LEAP tomography reveals dissolution of the clusters, with nearly uniform distribution of arsenic atoms in CdTe. Since the arsenic fraction (fAs) is 1 × 1018 cm−3, but the hole density ranges from 7.5 to 9.5 × 1015 cm−3, we hypothesize that a large fraction of the arsenic has been incorporated into interstitial sites or cadmium substitutional sites, resulting in limited dopant activation. 

Abstract Quantum semiconductor structures are commonly achieved by bandgap engineering, which relies on the ability to switch from one semiconductor to another during their growth. Growth of a superlattice is typically demanding technologically. In contrast, accumulated evidence points to a tendency among a certain class of multiple‐cation binary oxides to self‐assemble spontaneously as superlattice structures. This class is dubbed the homologous superlattices. For a famous example, when a mixture of indium and zinc is oxidized, the phases of In‐O and ZnO separate in an orderly periodic manner, along the ZnO polar axis, with polarity inversion taking place between consecutive ZnO sections. The same structure is observed when the indium is replaced with other metals, and perhaps even in ZnO alone. This peculiar self‐assembled structure is attracting research over the past decade. The purpose of this study is to gain understanding of the physics underlying the formation of this unique structure. Here, an explanation is proposed for the long‐standing mystery of this intriguing self‐assembly in the form of an electrostatic growth phenomenon and a test of the proposed model is carried out on experimental data.