Impact of graded doping transition layer on structural properties of Zr-doped AlN epilayers

Zirconium doped AlN (AlN:Zr) epilayers hold significant promise for advanced electronic and quantum applications, including photoconductive semiconductor switches for high-voltage and high-power operations as well as quantum qubit and sensing technologies. Despite its potential, producing crack-free and high-quality AlN:Zr epilayers with high Zr concentrations has been challenging. The main obstacle is the significant atomic size difference between Zr and Al, which introduces a substantial lattice mismatch between the AlN:Zr epilayer and the AlN bulk substrate. This study investigates the impact of graded doping transition layer on structural and compositional properties of AlN:Zr by employing in situ doping using metal-organic chemical vapor deposition growth technique. Structural and compositional properties were analyzed in detail using x-ray diffraction (XRD), transmission electron microscopy, and energy dispersive spectroscopy. The implementation of the graded transition layer led to significant structural improvements, including reduced XRD linewidth, decreased threading dislocations, and lower concentrations of Al vacancies, and enabled the realization of a crack-free AlN:Zr epilayer with a high Zr doping concentration of 8.2 × 1020 cm−3. These results demonstrate the effectiveness of the graded transition layer in producing high-quality AlN:Zr layers.