Crystalline (Al_1-xB_x)PSi₃ and (Al_1-xB_x)AsSi₃ tetrahedral phases via reactions of Al(BH₄)₃ and M(SiH₃)₃ (M = P, As)

Crystalline Al_1-xB_xPSi₃ alloys (x = 0.04-0.06) are grown lattice-matched on Si(100) substrates by reactions of P(SiH₃)₃ and Al(BH₄)₃ using low pressure CVD. The materials have been characterized for structure, composition, phase purity, and optical response by spectroscopic ellipsometry, high-resolution X-ray diffraction, high-resolution transmission electron microscopy, electron energy loss spectroscopy, and energy dispersive spectroscopy, which indicate the formation of single phase monocrystalline layers with tetrahedral structures based on AlPSi₃ parent phase. The latter comprises interlinked AlPSi₃ tetrahedra forming a cubic lattice in which the Al-P pairs are imbedded within a diamond-structured Si matrix as isolated units. Raman scattering of the Al_1-xB_xPSi₃ films supports the presence of substitutional B in place of Al and provides strong evidence that the boron is bonded to P in the form of isolated pairs, as expected on the basis of the AlPSi₃ prototype. The substitution of small size B atoms is facilitated by the stabilizing effect of the parent lattice, and it is highly desirable for promoting full lattice matching with Si as required for Si-based solar cell designs. The substitution of B also increases the bond-length disorder leading to a significantly enhanced absorption relative to crystalline Si and AlPSi₃ at E < 3.3 eV which may be beneficial for PV applications. Analogous reactions of As(SiH₃)₃ with Al(BH₄)₃ produce Al_1-xB_xAsSi₃ crystals in which the B incorporation is limited to doping concentrations at 10²⁰ atoms/cm³. In both cases the classical Al(BH₄)₃ acts as an efficient delivery source of elemental Al to create crystalline group IV-III-V hybrid materials comprising light, earth abundant elements with possible application in the fields of Si-based technologies and light-element refractory solids.