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We achieved the successful fabrication of Sn-doped α-Ga 2 O 3 thin films with higher electron mobility and wider conductivity controls by improving the crystal quality. α-Ga 2 O 3 films showed n-type conductivity with a maximum electron mobility of 24 cm 2 V %1 s %1 . The carrier concentration was successfully controlled in the range of 10 17 -10 19 cm %3 . Crystal defects such as dislocations severely compensate the free carriers in α-Ga 2 O 3 films and restrict the mobility at low carrier concentrations. Therefore, to achieve further conductivity control and higher mobility, improving the crystallinity of α-Ga 2 O 3 films is necessary.

The recent progress and development of corundum-structured III-oxide semiconductors are reviewed. They allow bandgap engineering from 3.7 to ∼9 eV and function engineering, leading to highly durable electronic devices and deep ultraviolet optical devices as well as multifunctional devices. Mist chemical vapor deposition can be a simple and safe growth technology and is advantageous for reducing energy and cost for the growth. This is favorable for the wide commercial use of devices at low cost. The III-oxide semiconductors are promising candidates for new devices contributing to sustainable social, economic, and technological development for the future.

Following the previous achievement of highly crystalline α-Ga2O3 thin films on c-plane sapphire, the growth of corundum-structured α-(Al x Ga1-x )2O3 was examined aiming at the future application of α-(Al x Ga1-x )2O3/Ga2O3 heterostructures to power devices and other functional devices. The results show the control of x and band gap up to 0.81 and 7.8 eV, respectively, maintaining the dominant corundum structure. The transmission electron microscope observation suggested the formation of the crystallographically good interface of α-(Al x Ga1-x )2O3/Ga2O3 without the severe generation of threading dislocation lines from the interface.

Highly crystalline corundum-structured -(Ga 1Àx Fe x ) 2 O 3 alloy thin films were fabricated on c-plane sapphire substrates by using a mist chemical vapor deposition method. The full-widths at half maximum of X-ray diffraction rocking curves were smaller than 100 arcsec for the entire range of x from 0 to 1. Optical band gaps were artificially tuned to a value between those of -Ga 2 O 3 and -Fe 2 O 3 , that is, 2.2 and 5.3 eV with changing the Fe content x in the films. Magnetic measurements revealed ferromagnetic properties of a -(Ga 1Àx Fe x ) 2 O 3 (x ¼ 0:24) thin film at 110 K.