Alloyed β-(Al xGa1- x)2O3bulk Czochralski single β-(Al0.1Ga0.9)2O3and polycrystals β-(Al0.33Ga0.66)2O3, β-(Al0.5Ga0.5)2O3), and property trends

Abstract

In this work, bulk Czochralski-grown single crystals of 10 mol. % Al2O3 alloyed β-Ga2O3 - monoclinic 10% AGO or β-(Al0.1Ga0.9)2O3 - are obtained, which show +0.20 eV increase in the bandgap compared with unintentionally doped β-Ga2O3. Further, growths of 33% AGO - β-(Al0.33Ga0.67)2O3 - and 50% AGO - β-(Al0.5Ga0.5)2O3 or β-AlGaO3 - produce polycrystalline single-phase monoclinic material (β-AGO). All three compositions are investigated by x-ray diffraction, Raman spectroscopy, optical absorption, and 27Al nuclear magnetic resonance (NMR). By investigating single phase β-AGO over a large range of Al2O3 concentrations (10-50 mol. %), broad trends in the lattice parameter, vibrational modes, optical bandgap, and crystallographic site preference are determined. All lattice parameters show a linear trend with Al incorporation. According to NMR, aluminum incorporates on both crystallographic sites of β-Ga2O3, with a slight preference for the octahedral (GaII) site, which becomes more disordered with increasing Al. Single crystals of 10% AGO were also characterized by x-ray rocking curve, transmission electron microscopy, purity (glow discharge mass spectroscopy and x-ray fluorescence), optical transmission (200 nm-20 μm wavelengths), and resistivity. These measurements suggest that electrical compensation by impurity acceptor doping is not the likely explanation for high resistivity, but rather the shift of a hydrogen level from a shallow donor to a deep acceptor due to Al alloying. Bulk crystals of β-(Al0.1Ga0.9)2O3 have the potential to be ultra-wide bandgap substrates for thin film growth, with a lattice parameter that may even allow higher Al concentration β-Ga2O3 single crystal thin films to be grown.