Optical absorption and photoconductivity at the band edge of beta-Ga2-xInxO3

Single crystals of beta-Ga(2-x)Ln(x)O(3) with x = 0 to 0.2 have been gown by the float zone technique using radiation heating. When x increases from 0 to 0.2, the interionic distance O-Ga in the gallium octahedron and tetrahedron increase on the average by 1 to 1.5% and, as a consequence, the position of the steep absorption edge of band-to-band electron transitions shifts towards smaller energies by 0.3 eV. Simultaneously, a strong and broad absorption band in the energy range 3.5 to 4.5, eV appears, caused by charge transfer electron transitions from 2p oxygen to 5s indium energy levels in octahedral indium clusters.