Polar-Twinned Defects in LiGaO₂ Substrates Lattice Matched With GaN

Materials Research Society Symposium Proceedings 468, 155 (1997).

Below is the abstract submitted to the meeting, not the abstract of the published paper:
LiGaO₂ crystal is orthorhombic with cell dimensions a=5.402 Å b=6.372 Å and c=5.007 Åand the crystal structure is similar to that of wurzite. The lattice mismatch to hexagonal GaN is only 0.9%. Single crystals of LiGaO₂ were grown using the Czochralski pulling method, Crossed lines were observed in mechano-chemically polished {001}-oriented wafers sliced from a [001] axis boule. Chemical etching also revealed that there exists a difference in chemical stability between the two domains separated by the crossed line. Since LiGaO₂ single crystal is polar along the c-axis, the formation of unique domain boundary is presumably attributable to the polarity inversion of the c axis, that is, the polar-twin boundary. This polarity inversion is associated with a phase transition below the melting temperature, which was verified by means of DTA experiments. C-axis oriented GaN thin films (thickness: ∼500 Å) were grown on (001) LiGaO₂ substrates by MBE. The X-ray rocking curves of (0002) reflection of the grown films were different for each measured area. The surface morphologies observed with AFM were also different for each domain separated by the crossed line. Further investigation into the interface between the substrate LiGaO₂ and the GaN film and/or growth mode is underway to clarify the suitability of LiGaO₂ as a substrate for GaN.

This paper is part of Gallium Nitride and Related Materials II

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