Alternative alloy to increase bandgap in gallium Oxide, β-(ScxGa1-x)2O3, and rare earth Stark luminescence

Abstract

β-Ga2O3 is an emergent ultrawide bandgap material, which has been recently studied with respect to alumina alloying in order to tailor the bandgap for thin film or bulk applications. In this work, bulk Czochralski and vertical gradient freeze crystals of 6 – 8 mol.% Sc2O3 alloyed β-Ga2O3 (SGO) – β-(Sc0.06Ga0.94)2O3 to β-(Sc0.08Ga0.92)2O3 – were obtained, which showed a nominal + 0.07 eV increase in the optical bandgap compared to unintentionally doped (UID) β-Ga2O3. SGO was characterized for structure (X-ray diffraction, rocking curve, nuclear magnetic resonance, Raman microscopy), purity (glow discharge mass spectrometry, X-ray fluorescence), optical transmission (200 nm – 25,000 nm), resistivity, and luminescence (laser induced luminescence microscopy, photoluminescence). Structural measurements indicate successful incorporation of Sc, although overall lower quality than UID and β-(Al0.1Ga0.9)2O3 (AGO) material. Purity and optical measurements demonstrated few acceptor impurities and a widened band gap, although not wide enough for some donors to become deep enough to promote insulating behavior. Bulk SGO crystals demonstrated intense Stark luminescence transitions characteristic of Nd3+, presumably an impurity in the Sc2O3 powder, with some areas of the crystal showing highly concentrated Nd3+. Despite demonstrating an enlarged bandgap, scandia alloyed β-Ga2O3 retained electrical conduction similar to UID β-Ga2O3, unlike alumina alloyed β-Ga2O3 which was electrically insulating.