Corundum-structured gallium oxide (a-Ga₂O₃), due to its expectably high breakdown electric field judging from wide band gap of 5.3 eV, is a novel candidate for high-voltage power devices as well as deep ultraviolet photonic devices.  Band gap engineering is the basic requirements for heterostructure device applications, and has basically been achieved by alloying two or more binary semiconductors of the same crystal structure.  We have showed the band gap engineering with a-(AlGa)₂O₃ from 5.3 to 7.8 eV for Al concentration from 0 to 0.81, keeping well-defined corundum structure [1].  The next target study is the band gap engineering with a-(InGa)₂O₃, which has been ready owing to our recent demonstration of a-In₂O₃ grown by the mist chemical vapor deposition (CVD) method [2].  The band gap engineering with these ternary alloys will be followed by the composition control of a-(AlGaIn)₂O₃ quaternary alloys, which will achieve a variety of heterostructures with unique properties, like (AlGaIn)N.  In this presentation we will show the growth characteristics of a-(InGa)₂O₃ alloys.

    The growth of α-(In_xGa_1-x)₂O₃ was achieved by using α-Ga₂O₃ buffer layers on c-plane sapphire substrates by the mist CVD method, which is a safe technology with low energy consumption allowing the growth of high-quality α-Ga₂O₃ [3].  The growth temperature was 500 ^oC.  The growth time of an α-Ga₂O₃ buffer layer and α-(In_xGa_1-x)₂O₃ were kept at 1 and 30 minute, respectively.  Here gallium(III) acetylacetonate and indium(III) acetylacetonate were used as the sources of Ga and In, respectively.

    Fig.1 is the results of XRD measurement of α-(In_xGa_1-x)₂O₃ which has been grown by intentionally changing the In concentration x.  The systematic shift of the XRD peaks suggests the successful growth of α-(In_xGa_1-x)₂O₃ alloy thin films with x = 0, 0.05, 0.08, 0.67.  Fig 2 shows the band gap and resistivity in terms of the In concentration.  The band gap was calculated from the transmittance of the films, and was moderately changed with x. The resistivities were calculated from the value of the sheet resistance meter. The drastic decrease of resistivity was confirmed by slight addition of In (x = 0.05, 0.08) to α-Ga₂O₃, suggesting significant enhancement of semiconductor properties without marked reduction of the band gap. At the conference the detailed electrical and optical properties of α-(In_xGa_1-x)₂O₃ alloy thin films will be shown to discuss their potential for wide band gap device applications.

References

[1] H.Ito, K.Kaneko, and S.Fujita, Jpn. J. Appl. Phys. 51 (2012) 100207.

[2] N.Suzuki, K.Kaneko, and S.Fujita, J. Cryst. Growth 364 (2013) 30.

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1. Epitaxial growth of wide band gap oxide semiconductor thin films