High electron concentration and mobility in Al-doped _n -Z _nO epilayer achieved via dopant activation using rapid-thermal annealing

We report on the growth of very high-quality Al-doped n -type ZnO epilayers on sapphire substrates using a radio-frequency (rf) magnetron sputtering technique combined with a rapid-thermal annealing. Photoluminescence (PL) and Hall measurements show that both the optical and electrical properties of the ZnO layers are significantly improved with an increasing annealing temperature up to 900 °C. For example, the samples that are grown at 600 °C and a rf power of 100 W with an Ar O2 gas ratio of 1 give an electron concentration of 1.83× 1020 cm3 and a mobility of 65.6 cm2 V s, when annealed at 900 °C for 3 min in a nitrogen ambient. Furthermore, x-ray diffraction measurements show that both the as-grown and annealed samples are of excellent crystallinity.