Synthesis of heteroepitaxial BP and related Al-B-Sb-As-P films via CVD of Al(BH₄)₃and MH₃(M=P, As, Sb) at temperatures below 600 °C

Low temperature chemical vapor deposition using the Al(BH4)3 and PH3 precursors at ∼600 °C produces pure and crystalline BP films directly on Si and on ZrB2 buffer layers with no sign of Al incorporation. The BP films on ZrB2 are epitaxial despite the structural difference between the hexagonal buffer and the cubic epilayer. Density functional theory calculations of the interface energies revealed strong bonding interactions at the heterojunction due to compliant lattice matching behavior, corroborating the favorable assembly of BP on ZrB2. A systematic study of the growth method is carried out by substituting As and Sb for P in the group-V carrier gas. Reactions of Al(BH4)3 with AsH3 at 320 °C yielded the expected BAs films with small amounts of Al. In this case the samples are amorphous and efforts to crystallize them by increasing the growth temperature yielded boron-rich analogues. Analogous reactions of Al(BH4)3 with SbD3 on Si at 300 °C produce AlSb epitaxial crystals doped with B instead of the BSb phase. This indicates that the process favors formation of Al-Sb bonds over the weaker B-Sb bonds. The results of this study indicate that the Al(BH4)3 approach represents a viable low-temperature route that may be advantageous in producing useful BP coatings with applications in thermal and optical technologies. The compound also represents an intriguing low-temperature route to BP, BAs, and AlSb type materials when reacted with corresponding P, As, and Sb hydrides, yielding in each case the thermodynamically driven products.