Enhanced structural and optical properties of semipolar (⁠ $11 2 ¯ 2$⁠) AlGaN film with insertion of AlN/AlGaN superlattice

The high-quality semipolar (⁠ $11 2 ¯ 2$⁠) AlGaN films with high Al contents were successfully deposited on (⁠ $10 1 ¯ 0$⁠) m-plane sapphire substrates with the insertion of AlN/AlGaN superlattice (SL) by metal-organic chemical vapor deposition technology. The dependence of structural and optical properties of the (⁠ $11 2 ¯ 2$⁠) AlGaN film on the deposition parameters for the inserted AlN/AlGaN SL was investigated extensively premised on the characterization results of the optical microscope, atomic force microscopy, relative optical transmittance spectroscopy, high-resolution x-ray diffraction, and photoluminescence spectroscopy. It was discovered that the insertion of the AlN/AlGaN SL grown under an optimized stabilization time of 10 s between the deposition of AlN and AlGaN sublayers could be used to make significant enhancements in surface morphological characteristics, crystal quality, and optical properties of the (⁠ $11 2 ¯ 2$⁠) AlGaN film. The mechanism for the defects reduction in the (⁠ $11 2 ¯ 2$⁠) AlGaN film was revealed to be owing to the increase in bending and annihilating probability of the threading dislocations, basal-plane stacking faults, and other structural defects promoted by introducing sufficiently high desorbed Ga atom-induced vacancy concentration in the optimized thermal treatment process.