Microstructure of non-polar GaN on LiGaO 2 grown by plasma-assisted MBE
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NANO EXPRESS
Open Access
Microstructure of non-polar GaN on LiGaO2 grown by plasma-assisted MBE Cheng-Hung Shih1, Teng-Hsing Huang2, Ralf Schuber3*, Yen-Liang Chen1, Liuwen Chang2, Ikai Lo1, Mitch MC Chou2 and Daniel M Schaadt3
Abstract We have investigated the structure of non-polar GaN, both on the M - and A-plane, grown on LiGaO2 by plasmaassisted molecular beam epitaxy. The epitaxial relationship and the microstructure of the GaN films are investigated ¯ GaN ||[010]LGO and by transmission electron microscopy (TEM). The already reported epi-taxial relationship [1120] ¯ (1100) GaN ||(100)LGO for M -plane GaN is confirmed. The main defects are threading dislocations and stacking faults in both samples. For the M -plane sample, the density of threading dislocations is around 1 × 1011 cm-2 and the stacking fault density amounts to approximately 2 × 105 cm-1. In the A-plane sample, a threading dislocation density in the same order was found, while the stacking fault density is much lower than in the M -plane sample. Introduction Gallium nitride (GaN), as one of the most important wide band semiconductors today, has far-reaching applicability in electronic and optoelectronic devices. Its hexagonal crystal structure, however, exhibits a polar axis in the [0001] direction along which a polarization is present. The resulting polarization fields lead to intrinsically existent internal electric fields which give rise to a strong quantum-confined Stark effect when group IIInitride heterostructures are grown along the [0001] direction. As a consequence, electrons and holes are spatially separated in such structures, leading to a reduced wave function overlap and a decreased radiative transition energy. One way to circumvent these unwanted effects is to use non-polar surfaces of the hexagonal nitride structure ¯ ¯ for episuch as the M -plane {1100} and A-plane {1120} taxial growth procedures. The lack of available substrates for homoepitaxy on non-polar crystal planes requires alternative substrates for heteroepitaxy. While various substrates have been considered for this purpose, LiGaO2 (LGO) presents the unique opportunity for growth of C -, M -, and A-plane-oriented GaNs on a very well lattice-matched substrate, depending on the substrate surface orientation used. C -plane GaN growth * Correspondence: [email protected] 3 Institute for Applied Physics/DFG-Center for Functional Nanostructures (CFN), Karlsruhe Institute of Technology, 76131 Karlsruhe, Germany Full list of author information is available at the end of the article
has been demonstrated on (001) LGO by a number of groups, e.g. [1]. Recently, M - and A-plane GaN growth has been reported on (100) LGO [2] and (010) LGO [3], respectively. In this article, we demonstrate a first analysis of M and A-plane GaN films on LGO showing strong evidence for a high-phase purity of non-polar GaN. The TEM studies confirm the epitaxial relationship of M -plane GaN on (100) LGO and A-plane GaN on (010) LGO and give insight to their defect structure.
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