Spectroscopy of Defects in Gallium Oxide
Ritter, Jacob Rudolph
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β-Gallium oxide (β-Ga2O3) is a promising semiconductor for its potential as a material in the field of power electronics. Magnesium doping of Ga2O3 has been shown to create a semi-insulating material, which could be utilized in ultrahigh-power devices. The properties of iridium impurities in undoped, magnesium-doped, and calcium-doped gallium oxides were investigated with IR spectroscopy. In undoped and Ca-doped β-Ga2O3, IR peaks at 3313, 3450, and 3500 cm-1 are tentatively assigned to O–H bond stretching modes of IrH complexes. Hydrogen-annealed Ga2O3:Mg shows an IR peak at 3492 cm-1, and H-annealed Ga2O3: Ca shows an IR peak at 3441 cm-1¬. These are assigned to an O-H bond-stretching mode of a neutral MgH and CaH complex, respectively. Polarization experiments were used to place the O-H bond of the MgH complex in the a-c plane. Mg, Ca, and Fe doped samples show an Ir4+ electronic transition feature at 5148 cm 1. By measuring the strength of this feature versus photoexcitation, the Ir3+/4+ donor level was determined to lie 2.2-2.3 eV below the conduction band minimum, which matches theory. Ga2O3:Mg also has a range of sidebands between 5100 and 5200 cm-1, attributed to IrMg pairs. Polarized IR measurements were used to show that the 5148 cm-1 peak is anisotropic, weakest for light polarized along the c axis.