Rational design of monocrystalline (InP)_yGe_5-2y/Ge/ Si(100) semiconductors: Synthesis and optical properties

In this work, we extend our strategy previously developed to synthesize functional, crystalline Si_5-2y(AlX)_y {X = N,P,As} semiconductors to a new class of Ge-III-V hybrid compounds, leading to the creation of (InP)_yGe_5-2y analogues. The compounds are grown directly on Ge-buffered Si(100) substrates using gas source MBE by tuning the interaction between Ge-based P(GeH₃)₃ precursors and In atoms to yield nanoscale "In-P-Ge₃" building blocks, which then confer their molecular structure and composition to form the target solids via complete elimination of H₂. The collateral production of reactive germylene (GeH₂), via partial decomposition of P(GeH ₃)₃, is achieved by simple adjustment of the deposition conditions, leading to controlled Ge enrichment of the solid product relative to the stoichiometric InPGe₃ composition. High resolution XRD, XTEM, EDX, and RBS indicate that the resultant monocrystalline (InP) _yGe_5-2y alloys with y = 0.3-0.7 are tetragonally strained and fully coherent with the substrate and possess a cubic diamond-like structure. Molecular and solid-state ab initio density functional theory (DFT) simulations support the viability of "In-P-Ge₃" building-block assembly of the proposed crystal structures, which consist of a Ge parent crystal in which the P atoms form a third-nearest-neighbor sublattice and "In-P" dimers are oriented to exclude energetically unfavorable In-In bonding. The observed InP concentration dependence of the lattice constant is closely reproduced by DFT simulation of these model structures. Raman spectroscopy and ellipsometry are also consistent with the "In-P-Ge ₃" building-block interpretation of the crystal structure, while the observation of photoluminescence suggests that (InP)_yGe _5-2y may have important optoelectronic applications.