Atomic-scale characterization of structural and electronic properties of Hf doped β-Ga2O3 (original) (raw)

In this letter we investigate the atomic and electronic structure of Hf-doped β-Ga2O3 single crystal using high resolution scanning transmission electron microscopy imaging and electron energy loss spectroscopy. UV-vis-NIR absorption measurements and density functional theory calculations are performed to further connect the nanoscale observation to the macroscale properties arising from the atomic structure. The Hf-doped sample was grown from the melt with a nominal Hf concentration of 0.5%at. We show that the Hf dopants prefer to occupy octahedral over tetrahedral sites by 0.68 eV and have some resistance to form precipitates due to a repulsive interaction of 0.17 eV between Hf atoms on neighboring sites. Also, the presence of Hf atoms on either tetrahedral or octahedral sites do not significantly affect the crystal structure of β-Ga2O3. Finally, the bandgap values of the Hf doped β-Ga2O3 obtained by EELS and UV-Vis-spectroscopy were Eg = 4.83 ± 0.1 eV and 4.75 ± 0.02 eV respectively, similar to the values reported for unintentionally doped β-Ga2O3 crystals. All these results make Hf an excellent dopant candidate for β-Ga2O3. The most thermally stable polymorph of Ga2O3, beta-gallium oxide (-Ga2O3), is an exciting semiconductor that combines an ultrawide bandgap (Eg ~ 4.8 eV) with a reasonable mobility (~ 100 cm 2 /V) and a high breakdown field with a predicted value of 8 MV/cm: properties which makes it a great candidate in high-power electronics, optical devices, and gas sensing detectors [1, 2]. In addition, the flexibility and tunability of its electronic properties, that can be achieved through doping, makes it an extremely promising candidate for future electronic device design [3]. Several dopants for -Ga2O3 have been studied, including Si, Sn, Ge, Ta and Nb, resulting in free-electron densities ranging from 1 x 10 17 to 2 x 10 19 cm-3 and mobilities from 25 to 130 cm 2 /V•s [4, 5, 6, 7, 1, 8]. These dopants thus have been shown to allow tunable ntype conductivity in -Ga2O3 [4, 5, 6, 7, 1], enabling applications like charge-transfer devices and optoelectronic devices. Saleh et al. have recently studied Zr as an alternative dopant and demonstrated tunable n-type conductivity in Zr-doped bulk -Ga2O3 grown from the melt, with