GaAlN/GaN HEMT heterostructures grown on SiCopSiC composite substrates for HEMT application

Abstract This paper reports on low-pressure metalorganic vapour deposition (LP-MOCVD) growth optimisation of GaAlN/GaN heterostructures grown on SiCopSiC (silicon carbide-oxyde-polycrystalline silicon carbide) composite substrates for HEMT applications, and on the first device performances obtained with these structures. Some critical growth parameters, such as growth temperature, V/III ratio and nucleation layer at the GaN/SiC interface, have been investigated, and their impact on physical properties of these heterostructures is studied. Such optimisation of the growth conditions has led to GaAlN/GaN HEMT heterostructures which are successfully compared in terms of material quality to the standard HEMT heterostructures grown on bulk SiC substrates. Their electrical characteristics, such as sheet carrier density ( N s ), mobility ( μ ), pinch-off voltage ( V p ) or sheet resistance ( R s ), are very similar to those obtained on bulk SiC substrates and their crystallographic properties, assessed by high-resolution X-ray diffraction (HR-XRD), transmission electron microscopy (TEM) and atomic force microscopy (AFM), seem to be in good agreement with the above-mentioned electrical characteristics. First devices with 0.5 μm gate length, made on these specific composite wafers, exhibit very good microwave performances, with output power of 5 W/mm at 10 GHz, similar to those obtained on bulk SiC substrates, showing the promising capability of SiCopSiC composite substrates.