RESEARCH INTERESTS

My research activities bridge the areas of inorganic chemistry, applied physics and materials science of semiconductor and refractory materials. The design, preparation and applications of novel solid state and molecular systems are particularly emphasized. Current thrusts include: (a) synthesis of purpose-built, main group inorganic hydrides with tailored reactivities and stoichiometries, enabling formation of functional material architectures that cannot be obtained by conventional routes, (b) growth of silicon-based photonic materials for the development of prototype photodetectors, modulators, and multijunction photovoltaic devices, (c) integration of dissimilar materials with Si technologies (including III-V and II-VI compounds for monolithic integration) via epitaxy driven synthesis methods, (d) advanced wide band gap semiconductor materials for breakthrough applications in solar energy, solid state lighting and optoelectronics semiconductors, (e) solid-state inorganic chemistry based on light elements (refractory carbides, nitrides, borides and C-N frameworks).

 

 

Mono-crystalline, silicon-like (III-V)-(IV)3  and (III-V)y -IV5-2y semiconductors

(III: B, Al, Ga, In)  (V: N, P, As, Sb)  (IV: Si, Ge)

We explore synthesis of a new class of hybrid tetrahedral semiconductors consisting of alloys of group-IV and III-V compounds that are inaccessible using traditional methods.  The work is based on a recently discovered methodology in our labs  that combines III-V and group-IV materials in a manner that eliminates phase segregation issues that until now prevented the development of these materials for applications in optoelectronics. The approach involves use of purposely assembled molecular building blocks that incorporate fully pre-formed tetrahedral units to create single phase monocrystalline epilayers via epitaxy driven mechanisms.  The project includes the rational design and development of main-group hydrides with precisely tailored structures and stoichiometries at the nanoscale that enable the generalization of the approach. These precursors are then used for crystal growth of new semiconductors with natural formula (III-V)(IV)3, on silicon, germanium and other industrially relevant platforms. The structural and optical properties of the resultant crystals are fully explored.  Ab initio simulations are used to guide the selection of target systems with potentially attractive properties.

AlPSi3

While this new method was initially introduced to grow new mono-crystalline compounds such as Si3AlP (see figure above), Si3AlAs, and Si3Al(As1-xPx) as well as corresponding alloys Si3Al(As1-xNx), Si3Al(P1-xNx), Al(As,P,N)ySi5-2y and (InP)yGe5-2y, it can be generalized to include most group IV and III-V elements. We have demonstrated that judicious alloying of the group V sublattice allows tuning of structural and optical properties, including perfect lattice matching to silicon, in the general Al(As,P,N)ySi5-2y class of compounds. The synthesized materials may have applications in various fields of optoelectronics, including direct-gap laser materials on Si and semiconductors with widely tunable band gaps for high efficiency photovoltaics.  The latter potential is explored in collaboration with colleagues at the National Renewable Energy Labs (NREL).
This is a project for students who are interested in hands-on experiments involving epitaxy driven synthesis of new optical semiconductors and characterization of structure/composition/ property relationships.  Methods of synthesis include gas source molecular beam epitaxy and ultra-high vacuum chemical vapor deposition.  No prior experience is necessary, but epitaxial growth and characterization of device quality materials and evaluation of their optical/electrical properties including photovoltaic performance requires a strong motivation and commitment.

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Highlights:
  • Property tuning by alloying on the group V sublattice of IV/III-V semiconductors: Synthesis of Al(P1-xAsx)Si3
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  • Synthesis of main-group inorganic hydrides for applications in materials science.
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  • Silicon-based photonic materials: growth and devices (photodetectors, modulators and emitters). 
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  • Epitaxial integration of dissimilar materials with Si (including III-V and II-VI compounds for monolithic integration). 
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  • Optoelectronic wide band gap semiconductors.
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  • Solid-state inorganic chemistry based on light elements (refractory carbides, nitrides, borides and C-N frameworks).
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