Abstract
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 Ec − 1.6 eV level. The Sn:α-Ga2O3 film grown on the strained 20-nm heterostructure buffer showed best characteristics overall.
Highlights
It has been shown that the dislocation density, which was typically high in undoped α-Ga2O3,14–16 could be reduced by the use of a complicated α-(AlxGa1−x)2O3 heterostructure buffer grown via mist CVD,11 epitaxial lateral growth via halide vapor phase epitaxy (HVPE),14,15 or the growth of thick films
The heterostructure buffers consisted of six layers laying on top of each other, which were grown using the same recipe as the six single-layer buffers
For Sn-doped α-Ga2O3 (Sn):αGa2O3 films grown on single-layer buffers, the FWHM of the (0006) x-ray diffraction (XRD) rocking curves (RCs) abruptly increased as x exceeded 0.4, indicating the severe tilting of the mosaic blocks
Summary
The growth of (AlxGa1−x)2O3/Ga2O3 heterostructures has attracted large attention of the research community for the nextgeneration ultra-wide bandgap high power devices. Very highquality β-(AlxGa1−x)2O3/Ga2O3 heterostructures have been grown by plasma-assisted molecular beam epitaxy (PAMBE). Based on this work, β-(AlxGa1−x)2O3/Ga2O3 modulation-doped field-effect transistors have been demonstrated. On the other hand, a high Al content x can be realized in the α-phase (AlxGa1−x)2O3 because α-(AlxGa1−x)2O3 crystalizes in the same corundum structure as the sapphire substrate. Previously, mist chemical vapor deposition (mist CVD) has demonstrated its capability in growing complicated multi-layer corundum-type heterostructures.11–13It has been shown that the dislocation density, which was typically high in undoped α-Ga2O3,14–16 could be reduced by the use of a complicated α-(AlxGa1−x)2O3 heterostructure buffer grown via mist CVD, epitaxial lateral growth via halide vapor phase epitaxy (HVPE), or the growth of thick films. the effect of (AlxGa1−x)2O3 buffers with different Al-contents x on the scitation.org/journal/apm properties of subsequently grown conductive Sn-doped α-Ga2O3 (Sn:α-Ga2O3), in particular, on the dislocation density and conductivity, has not been systematically studied. Very highquality β-(AlxGa1−x)2O3/Ga2O3 heterostructures have been grown by plasma-assisted molecular beam epitaxy (PAMBE).. Β-(AlxGa1−x)2O3/Ga2O3 modulation-doped field-effect transistors have been demonstrated.. Mist chemical vapor deposition (mist CVD) has demonstrated its capability in growing complicated multi-layer corundum-type heterostructures.. It has been shown that the dislocation density, which was typically high in undoped α-Ga2O3,14–16 could be reduced by the use of a complicated α-(AlxGa1−x)2O3 heterostructure buffer grown via mist CVD, epitaxial lateral growth via halide vapor phase epitaxy (HVPE), or the growth of thick films.. The effect of (AlxGa1−x)2O3 buffers with different Al-contents x on the scitation.org/journal/apm properties of subsequently grown conductive Sn-doped α-Ga2O3 (Sn:α-Ga2O3), in particular, on the dislocation density and conductivity, has not been systematically studied
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