α-(AlxGa1?x)2O3 single-layer and heterostructure buffers for the growth of conductive Sn-doped α-Ga2O3 thin films via mist chemical vapor deposition

摘要

A third generation mist chemical vapor deposition (3rd G mist CVD) system was used to grow six single-layer and two heterostructure α -(AlxGa1?x)2O3 buffers on c -plane sapphire substrates for the subsequent deposition of conductive Sn-doped α -Ga2O3 (Sn: α -Ga2O3) thin films. In the six single-layer buffers, the Al contents x increased from 0 to 0.66. The two heterostructure buffers consisted of six ～20-nm- and ～100-nm-thick layers laying on top of each other. The 3rd G mist CVD system enabled the growth of these complicated multi-layer heterostructures in a single run, while mono-crystallinity was still maintained in all grown layers. Strain was observed in the 20-nm heterostructure, while the layers in the 100-nm heterostructure almost fully relaxed and the Vegard’s law was followed even when the α -(AlxGa1?x)2O3 layers were stacked on each other. Transmission electron microscopy analyses show that the dislocation densities remained high in the order of 1010 cm?2 despite the employment of the buffers. PtOx and AgOx Schottky diodes (SDs) were fabricated on the Sn: α -Ga2O3 films. The barrier height vs ideality factor plots could be fitted by linear dependences, indicating that the large ideality factors observed in α -Ga2O3 SDs could be explained by the inhomogeneity of the SDs. The extrapolation of the dependences for the PtOx and AgOx SDs yielded homogeneous Schottky barrier heights of ～1.60 eV and 1.62 eV, respectively, suggesting that the Fermi level was pinned at the E c ? 1.6 eV level. The Sn: α -Ga2O3 film grown on the strained 20-nm heterostructure buffer showed best characteristics overall.