Materials Science Forum Vols. 821-823

Abstract: Structural investigations of Si quantum dots (QDs) grown by CVD on two different heterostructures: AlN/Si (111) and 3C-SiC/Si (100) are conducted. The Si QDs have been grown using silane as precursor, diluted in hydrogen, at fixed temperature and pressure (830°C - 800mbar). High densities of dots can be obtained (up to 10¹¹ cm^-2) with typical heights below 10nm. The kinetic of deposition lets suppose the presence of an initial wetting layer before the dots formation. Different durations are required for nucleating dots on AlN and 3C-SiC. Si QDs on AlN present a luminescence band which can be attributed to quantum confinement.

Abstract: Aluminum nitride (AlN) bulk crystals, approximately 50.8mm in diameter and up to 5mm thickness, were grown by a physical vapor transport (PVT) method in a tantalum crucible. To investigate the effect of crucible materials, various crucible materials, a graphite and TaC-coated graphite and tantalum crucible were used for the AlN growth. XRD pattern of AlN crystal grown on SiC seed in the Ta-crucible exhibited only (00l) peaks, indicating that AlN single crystal was successfully grown on SiC seed. The interface structure between AlN and SiC crystals was observed by a high resolution TEM.

Abstract: We report on the growth method and the structural characterization of freestanding AlN crystals. An AlN layer is grown on a gradually decomposing SiC substrate yielding a freestanding crack free 2H single crystal with dislocation density 5×10⁴ cm^–2 and without grain boundaries as confirmed by synchrotron radiation phase contrast imaging and topography data. Wafers of 600–1000 μm thick and up to 15 mm in diameter are obtained. The thermal stress distribution in a conventional AlN/SiC structure is discussed. Theoretical estimates show that cracking of AlN layers is a natural result of their growth on undecomposed SiC substrates.

Abstract: We previously reported a unipolar mode p⁺-polycrystalline silicon (poly-Si)/4H-SiC heterojunction diode (SiC-HJD) [1-3]. In this work, we demonstrate a poly-Si/GaN vertical unipolar heterojunction diode (GaN-HJD) based on numerical simulation and experimental results. The GaN-HJD is expected to control the electrical characteristics of both Schottky action with a p-type poly-Si and ohmic action with an n-type poly-Si. We investigated the detailed physics of the GaN-HJD between p⁺ Si and n⁺ Si by numerical simulation. The GaN-HJD was also fabricated with p⁺-type polycrystalline silicon on an n^--type epitaxial layer on bulk GaN substrates. The measured barrier height of the GaN-HJD was 0.79 eV and the ideality factor was 1.10.