Growth and electron microscopy study of GaN/MgAl2O4 heterostructures
2010
We successfully grew Gallium nitride (GaN) films on MgAl 2 O 4 (111) substrates using low temperature pulsed laser deposition (PLD). X-ray diffraction rocking curves revealed the high quality of as-grown GaN with its full width at half maximum (FWHM) along [0002] as small as 0.08°. Atomic force microscopy images showed very smooth surface of as-grown GaN and indicated a two-dimensional growth. High-resolution transmission electron microscopy showed high structural perfection of GaN films. The crystalline structure for MgAl 2 O 4 substrate from its body to its top part adjacent to GaN epitaxy kept constant, and the interface between GaN and MgAl 2 O 4 was atomically abrupt. We attribute the high quality of as-grown GaN films to the well-controlled Mg atom evaporation from MgAl 2 O 4 substrate surface owing to the application of low growth temperature in PLD: on the one hand, it avoids the severe interfacial reaction that is very likely to take place in conventional MOCVD or MBE growth, and hence makes the epitaxial growth possible; on the other hand, it conserves the crystalline structure of the substrate surface, and consequently takes good advantage of the small lattice mismatch between GaN and MgAl 2 O 4 .
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