Cubic GaN/GaAs (001) heterostructures were grown by RF-plasma assisted molecular beam epitaxy with different GaN nucleation temperatures. The heterostructures were studied by an open cell configuration of a photoacoustic experiment to obtain the effective thermal diffusivity (α) of the composite, which presented values varying from 14 to 28mm2/s. Also, a two-layer model was used in order to obtain the interfacial thermal conductivity (η), revealing values from 5 to 35W/cm2 K. Both α and η presented higher values for cubic GaN films grown with higher nucleation temperatures. The crystalline quality of the samples, studied with high resolution x-ray diffraction and photoluminescence measurements, showed that the increase in the nucleation temperature produced films with fewer defects, implying a dependence between the interfacial thermal properties and the bulk crystalline quality. This variation of η can be associated with phonon scattering due to disorder at the interface region. The results provide an important understanding of how the growth temperature of the nucleation layer can affect the quality and the properties of the cubic GaN.

The self-assembling of nanovoids with a precisely controlled depth at the GaN/GaAs interface is reported and their formation mechanism discussed. During the very early stages of GaN growth by molecular beam epitaxy over GaAs(100) misoriented substrates, nano-pits are formed by chemical reactions of gallium and nitrogen with a GaAs sacrificial layer. The GaAs sacrificial layer is grown on top of a GaAs/AlGaAs superlattice that is used to efficiently stop the in-depth etch and to promote lateral etching. Thus, a nanostructure of wide voids and pedestals is self-assembled and confined at the interface. As an application, the lift-off of GaN epilayers from the substrate was carried out successfully, a fact that opens up the applicability of this process in other semiconductor systems.