Epitaxial growth of cubic crystalline semiconductor alloys on basal plane of trigonal or hexagonal crystal
Inventors
Park, Yeonjoon • Choi, Sang H. • King, Glen C.
Assignees
National Aeronautics and Space Administration NASA
Publication Number
US-7906358-B2
Publication Date
2011-03-15
Expiration Date
2028-10-20
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Abstract
Hetero-epitaxial semiconductor materials comprising cubic crystalline semiconductor alloys grown on the basal plane of trigonal and hexagonal substrates, in which misfit dislocations are reduced by approximate lattice matching of the cubic crystal structure to underlying trigonal or hexagonal substrate structure, enabling the development of alloyed semiconductor layers of greater thickness, resulting in a new class of semiconductor materials and corresponding devices, including improved hetero-bipolar and high-electron mobility transistors, and high-mobility thermoelectric devices.
Core Innovation
The invention provides hetero-epitaxial semiconductor materials comprising cubic crystalline semiconductor alloys grown on the basal plane of trigonal and hexagonal substrates. By approximately lattice matching the cubic crystal structure to the underlying trigonal or hexagonal substrate structure, the invention reduces misfit dislocations, enabling the development of alloyed semiconductor layers of greater thickness. This results in a new class of semiconductor materials and corresponding devices, including improved hetero-bipolar and high-electron mobility transistors, and high-mobility thermoelectric devices.
The problem addressed is the difficulty in growing group IV element alloys (such as SiGe) on substrates like silicon wafers due to lattice constant mismatches. Prior efforts tried to directly match cubic lattice constants, but even small mismatches caused high pressures and resulted in thin layers with high defect densities such as misfit dislocations. This challenge also applies to other cubic crystalline semiconductor materials, including group III-V and II-VI materials with zinc-blende structure, and materials with BCC and FCC structures.
The invention solves this by using new lattice-matching methods for rhombohedral growth of group IV alloys and other cubic crystalline materials on trigonal or hexagonal substrates. It involves calculating alloy compositions to approximately match substrate lattices based on the transformed atomic distances resulting from a rhombohedral transformation of cubic crystals along the <111> direction. This lattice matching technique allows growth of thicker, defect-reduced alloy layers with improved material properties for semiconductor devices.
Claims Coverage
The patent discloses one independent claim encompassing a method for forming a hetero-epitaxial crystal structure on trigonal or hexagonal substrates with minimized dislocation defects.
Method for lattice matching based on atomic site coincidence with or without rotation
The method calculates a target lattice constant (Ltarget) for the alloy by considering four types of atomic site coincidence lattice arrangements of the {111} plane of the alloy with the basal plane of the substrate: (a) direct coincidence without rotation, (b) coincidence with 30° rotation, (c) coincidence with inner vertices without rotation, and (d) coincidence with inner vertices with 30° rotation. Corresponding expressions for Ltarget are specified for each type.
Determination of alloy proportions using lattice constants and Bowing Parameter
The method determines the proportions of elements in the group IV, III-V, or II-VI alloy by approximating Ltarget as a linear function of the individual lattice constants of constituent elements weighted by their proportions and includes the use of a Bowing Parameter. Solving these approximations yields the alloy composition optimized for lattice matching.
Growing the hetero-epitaxial alloy on the basal plane to minimize dislocation defects
The method includes growing the determined alloy composition on the basal (0001) plane of the trigonal or hexagonal substrate to form the hetero-epitaxial crystal structure with reduced crystalline dislocation defects between the alloy and substrate layers.
The independent claim covers a method involving calculation of target lattice constants based on atomic lattice coincidence with or without rotation, composition determination using lattice constants and bowing parameters, and epitaxial growth on trigonal or hexagonal substrates to reduce crystalline dislocation defects.
Stated Advantages
Enables development of cubic crystalline semiconductor alloys substantially relieved from misfit dislocation defects on various substrates.
Allows incorporation of high contents of germanium and tin into silicon without the prior critical thickness limit, increasing built-in electric fields for faster devices.
Improves electron mobility in hetero-bipolar and high electron mobility transistors, enhancing performance beyond conventional Si transistors.
Facilitates more efficient thermoelectric devices through improved material crystal quality and higher carrier mobilities.
Documented Applications
Improved hetero-bipolar transistors (HBT) with high germanium and tin content alloy layers for enhanced electron mobility and device speed.
High electron mobility transistors (HEMT) utilizing lattice-matched cubic crystalline semiconductor alloys on trigonal or hexagonal substrates.
High-mobility thermoelectric (TE) devices based on alloy materials grown with reduced dislocation defects enabled by the lattice matching method.
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