InN offers important advantages such as a 0.7eV direct bandgap, large electron mobility, small effective mass and high saturation velocity, thus making it a promising material for various optoelectronics and microelectronics applications. It is thus highly desirable to achieve good quality epilayers, and heteroepitaxial growth of InN on Si(111) substrates could reduce the lattice mismatch to ~8%, in comparison to ~11% for growth on GaN(0001) buffer layers.  However, previous experimental work showed that a thin AlN/GaN buffer layer on Si improved the InN structural and electrical properties compared to InN nucleation directly on Si.

We report on the structural properties of a 2mm thick InN film grown on Si(111) by nitrogen radio-frequency plasma source MBE, using a buffer layer comprising 20nm AlN and 40nm GaN. Structural characterization was performed in cross section geometry using transmission electron microscopy (TEM), both conventional (XTEM) and high-resolution (HRTEM).  The film was single crystalline, and exhibited N-polarity. The double buffer layer and dislocation annihilation interactions in the first ~200nm reduced the threading dislocation density inside the film to ~2.3´10¹⁰cm^-2. At the AlN/GaN and GaN/InN interfaces, the roughness is enhanced by threading dislocations terminating at V-defects. This causes the introduction into the film of threading dislocations with c-type Burgers vector components in order to accommodate the interfacial roughness. Therefore the majority of threading dislocations propagating into the epilayer were of a+c mixed type. Strain measurements showed that all the layers were relaxed. The GaN/InN interface was found to comprise a regular array of misfit dislocations, and the InN lattice constants were found as follows: a_InN= 0.3529nm, c_InN= 0.5708nm. This structure can be considered as an appropriate III-N system for further developments in device fabrication.

Acknowledgement: Work supported under MRTN-CT-2004-005583 (PARSEM)

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