Monocrystalline Al(As1鈥?i>xNx)Si3 and Al(P1鈥?i>xNx)ySi5鈥?y Alloys with Diamond-like Str

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• 作者：John Kouvetakis ; Andrew V. G. Chizmeshya ; Liying Jiang ; Tylan Watkins ; Gordon Grzybowski ; Richard T. Beeler ; Christian Poweleit ; Jos茅 Men茅ndez
• 刊名：Chemistry of Materials
• 出版年：2012
• 出版时间：August 28, 2012
• 年：2012
• 卷：24
• 期：16
• 页码：3219-3230
• 全文大小：694K
• 年卷期：v.24,no.16(August 28, 2012)
• ISSN：1520-5002

文摘

The reaction of M(SiH₃)₃ (M = P, As) with Al atoms from a Knudsen cell has recently led to an entirely new approach to the synthesis of (III鈥揤)鈥?IV) alloys on Si substrates using gas-source molecular beam epitaxy. The main feature of these new materials is the presence of isolated 鈥渄onor鈥揳cceptor鈥?pairs within fully interlinked III鈥揤鈥?IV)₃ 鈥渂uilding blocks鈥? leading to highly stable and crystalline structures with average diamond-like symmetry. Examples include stoichiometric compounds Al(P鈥揂s)Si₃ as well as silicon-rich alloys (Si)_5鈥?y(AlP)_y. While these materials can be grown on Si with small mismatch strains, the complete elimination of the lattice mismatch may be important for applications such as photovoltaics which require thick films. Accordingly, in this paper we expand the above compositional space and explore the optical tuning potential in this new class of materials by introducing nitrogen onto the group V sublattice. We demonstrate that the addition of N(SiH₃)₃ into the reaction mixture under appropriate conditions readily yields novel Al(As_1鈥?i>xN_x)Si₃ and Al(P_1鈥?i>xN_x)_ySi_5鈥?y alloys which exhibit enhanced optical absorption with respect to silicon as evidenced by spectroscopic measurements indicating potential applications in Si-based photovoltaics. These materials can be grown as monocrystalline layers completely lattice matched on Si via substitution of As and P by the markedly smaller N atoms. First-principles studies of the reactivity trends are consistent with the finding that a large excess of the less reactive N(SiH₃)₃ is needed to incorporate even minor amounts of the N atoms in the alloy products, up to 11% in the case of AlAs_1鈥?i>xN_xSi₃ but only 3% in the case of AlP_1鈥?i>xN_xSi₃. Molecular calculations are then combined with solid-state simulations to elucidate the path from 鈥渕olecule to solid鈥?by quantifying the structural changes associated with the incorporation of the Al鈥揚鈥揝i₃, Al鈥揂s鈥揝i₃, and Al鈥揘鈥揝i₃ tetrahedral cores into the solid. The main conclusions of this study are that severe departures from tetrahedral symmetry in the Al鈥揘鈥揝i₃ building block thwart the assembly of a regular diamond lattice. This is in contrast to the AlAsSi₃ counterpart, which is found to exhibit near perfect tetrahedral symmetry in the crystalline state. All compounds are predicted to be thermodynamically stable relative to their elemental reference states.

Keywords:

g/action/doSearch?action=search&searchText=semiconductor+alloys&qsSearchArea=searchText">semiconductor alloys; g/action/doSearch?action=search&searchText=III%E2%88%92V+compounds&qsSearchArea=searchText">III鈭扸 compounds; g/action/doSearch?action=search&searchText=group+IV+semiconductors&qsSearchArea=searchText">group IV semiconductors; g/action/doSearch?action=search&searchText=photovoltaics&qsSearchArea=searchText">photovoltaics