Nanostructure-property control in AlPSi₃/Si(100) semiconductors using direct molecular assembly: Theory meets experiment at the atomic level

Recent theoretical and experimental studies of a new class of diamond-like group III-V/group IV alloys composed of neighboring Earth-abundant Al, Si, and P elements, with a common stoichiometry of AlPSi₃, indicate that these materials are promising candidates for high-performance top junctions in tandem solar cells integrated on low-cost Si platforms. These materials are grown lattice-matched on Si(100) via self-assembly of AlPSi₃-like tetrahedral units generated by reaction of molecular P(SiH₃) ₃ and Al atoms to form silicon crystal analogues, which are distinguished by intact Al-P bonding units distributed within a Si matrix. In this paper, aberration-corrected annular-dark-field imaging and atomic-column elemental mapping, are applied to characterize bonding configurations and elemental distributions in this intriguing family of monocrystalline solids. The detailed arrangements and chemical environment of Al-P and Si components have been identified for the first time and are found to be correlated with bulk optical behavior by directly comparing quantum simulations with experimental maps of the crystal structure along common crystallographic projections. The AlPSi₃ alloys exhibit uniform atomic-scale composition but variations in local bonding motifs, observed by element-selective imaging and corroborated by Raman scattering. From an electronic structure perspective, the materials show extended optical coverage in the visible range compared to Si, with minor variations dependent on specific ordering of Al-P and Si within the alloy network, as confirmed by ab initio simulation of the dielectric properties. This study lays the groundwork for a systematic approach to correlating fundamental properties to atomic structure and processing conditions, which should facilitate the development of the group III-IV-V family materials with applications in Si-based PV technologies.