Varying nitrogen background pressure; an efficient approach to improve electrical properties of MBE-grown GaAs1−xNx thin films with less atomic disorder

Abstract

Epitaxial GaAs1−xNx thin films were grown on GaAs (001) substrates through solid-source molecular beam epitaxy using an RF plasma source for incorporating nitrogen. We examined the thin films grown under different nitrogen background pressures (NBPs) using various ex-situ techniques. GaAs0.969N0.031 thin films grown under a high NBP of 5.5 × 10−6 Torr exhibited thickness variation-induced Pendellösung fringes, a smooth surface with few Ga droplets, and a high electron mobility of 4020 cm2/(Vs), all of which evidence the high crystal quality. This is attributed to the reduction in surface recombination centers at elevated nitrogen concentrations. A high intensity of the GaAs LO1 and low intensity of the GaN-like local vibrational mode of the relaxed films were observed, attributed to less atomic disorder in the alloys. GaAs0.969N0.031 thin films exhibited near-band emission at 1.14 eV, close to the ideal band gap of (In)GaAsN (∼1 eV). Moreover, the photoluminescence intensity of films annealed at 750 °C exhibited a ∼200-fold improvement over films annealed at 650 °C. Hence, superior-quality epitaxial GaAs0.0969N0.031 thin films grown through SS-MBE are an ideal substitute for (In)GaAsN in high-efficiency multijunction solar cell applications.