Zr doping in pulsed-laser-deposited α - Ga2O

The feasibility of zirconium doping of $\ensuremath{\alpha}$-${\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ grown by pulsed laser deposition is demonstrated. Targets with different zirconium contents are used to adjust the zirconium content in the thin films. Therefore, a two-step growth process is utilized, where first an undoped $\ensuremath{\alpha}$-${\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ thin film is grown as a high-temperature buffer layer and the zirconium-doped $\ensuremath{\alpha}$-${\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ layer is subsequently deposited at a lower growth temperature. Highly conductive thin films are obtained with resistivities as low as $3.3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}\phantom{\rule{0.2em}{0ex}}\mathrm{\ensuremath{\Omega}}\phantom{\rule{0.2em}{0ex}}\mathrm{cm}$. An electron mobility as high as $38\phantom{\rule{0.2em}{0ex}}{\mathrm{cm}}^{2}\phantom{\rule{0.2em}{0ex}}{\mathrm{V}}^{\ensuremath{-}1}\phantom{\rule{0.2em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$ is measured for a high free carrier density of $6.5\ifmmode\times\else\texttimes\fi{}{10}^{18}\phantom{\rule{0.2em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$. The crystallization in the $\ensuremath{\alpha}$-phase was confirmed by x-ray diffraction measurements. Further, a strong influence of the growth temperature on the zirconium incorporation is observed, which can be explained by the increased desorption of volatile ${\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ suboxides at high growth temperatures. Depth-resolved x-ray photoelectron spectroscopy measurements were employed to investigate the doping profile in the thin films. They reveal a strongly depth-dependent incorporation of the zirconium, with a decreased incorporation towards the surface. First Schottky barrier diodes on zirconium-doped $\ensuremath{\alpha}$-${\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ thin films with rectification ratios as high as 8.5 orders of magnitude at $\ifmmode\pm\else\textpm\fi{}3\phantom{\rule{0.2em}{0ex}}\mathrm{V}$ are presented.