Si doped GaN films grown by reactive co-sputtering of GaAs and Si

Abstract

Si doped GaN films were grown on sapphire by RF reactive co-sputtering of GaAs and Si in argon–nitrogen atmosphere at 700 °C. The incorporation of Si in the films was controlled by varying Si area coverage on GaAs target and argon to nitrogen ratio in sputtering atmosphere. X-ray diffraction shows significant stress relaxation and improvement in structural quality with the incorporation of Si in films deposited with 2%–12% Si area coverage and 10%–20% nitrogen in sputtering atmosphere. Resistivity and Hall measurements show that the films deposited with 5%–12% Si area coverage and 20% nitrogen in sputtering atmosphere exhibit resistivity of ∼1.5 × 10−2 Ω cm, along with carrier concentration of ∼2 × 1019 cm−3 and mobility in the range of 20–22 cm2/V-s. The film deposited with 10% nitrogen in sputtering atmosphere and 8% Si area coverage, exhibits high carrier concentration of 1.5 × 1020 cm−3 along with mobility of 7.1 cm2/V-s, resulting in the lowest resistivity of ∼6 × 10−3 Ω cm. The behavior of electrical parameters is explained by invoking carrier trapping and scattering at the grain boundaries, in conjunction with the observed changes in their structural quality. The film with high carrier concentration ∼1020 cm−3, exhibits strong free carrier effects, such as, plasma resonance in NIR, high reflectivity in IR and significantly larger optical gap of 3.60 eV, due to the combined effect of Burstein-Moss shift and band gap narrowing.