The function of a 60-nm-thick AlN buffer layer in n-ZnO/AlN/p-Si(111)

ZnO films were prepared on p-Si (111) substrates by using atomic layer deposition. High-resolution x-ray diffraction (XRD), scanning electron microscopy (SEM), x-ray photoelectron spectroscopy (XPS), photoluminescence (PL), and I-V measurements were carried out to characterize structural, electrical, and optical properties. After introducing a 60-nm-thick AlN buffer layer, the growth direction of the ZnO films was changed from [10] to [0002]. Meanwhile, the ZnO crystalline quality was significantly improved as verified by both XRD and PL analyses. It has been demonstrated that the reverse leakage current was greatly reduced with the AlN buffer layer. The valence band offsets have been determined to be 3.06, 2.95, and 0.83 eV for ZnO/Si, ZnO/AlN, and AlN/Si heterojunctions, respectively, and the band alignment of ZnO/Si heterojunction was modified to be 0.72 eV after introducing the AlN buffer layer. Our work offered a potential way to fabricate Si-based ultraviolet light-emitting diodes and improve the device performances.