Wide Bandgap Engineering of Beta-(Al, Ga)$lt;inf$gt;2$lt;/inf$gt;O$lt;inf$gt;3$lt;/inf$gt; Mixed Crystals

Bandgap tunable -(Al, Ga) 2 O 3 mixed crystals with different Al 3+ concentration were grown by the optical floating zone (OFZ) method. When the nominal Al 3+ doping concentration was close to 0.26, cracking appeared. The powder X-ray diffraction (XRD) revealed that -(Al, Ga) 2 O 3 mixed crystals kept the crystal structure of -Ga 2 O 3 without foreign phases and the lattice parameters decreased with the increasing Al 3+ concentration. 27 Al magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy showed that Al 3+ occupied Ga 3+ positions and the ratio of Al 3+ (IV)/ Al 3+ (VI) was about 1:3.The transmittance spectra were measured to investigate the bandgap of -(Al, Ga) 2 O 3 mixed crystals. Results showed that the bandgap increased continuously with the Al 3+ concentration increasing from 4.72 eV to 5.32 eV, which may extend the application of -Ga 2 O 3 crystal in optoelectronic devices operating at shorter wavelength.