Interfacial and electrical characterizations of PEALD-grown AlN/4H-SiC MOS structure: a type-I heterojunction for enhanced blocking performance
摘要
In this study, the physical, chemical, and electrical properties of aluminum nitride (AlN) films deposited on SiC substrates by plasma-enhanced atomic layer deposition (PEALD) are thoroughly investigated. The atomic force microscopy (AFM) images reveal AlN films exhibiting an exceptionally smooth surface with less than 1 nm roughness. The spectroscopic ellipsometry (SE) data demonstrate a refractive index of 1.95 at a wavelength of 632.8 nm. The X-ray photoelectron spectroscopy (XPS) depth profiling measurements record atomic ratios of Al and N in AlN bulk consistent with the designed stoichiometry. The calculated band alignments of the SiC/AlN heterostructure estimate the conduction band offset (ΔEC) and valence band offset (ΔEV) to 1.59 eV and 1.32 eV, respectively. The capacitance–voltage (C–V) measurements reveal the presence of a low interface state density of Dit = 7.83 × 1011 cm−2·eV−1 at EC−Et = 0.2 eV, an effective fixed charge density of Neff = 1.48 × 1012 cm−2, and near-interface traps of NITs = 6.88 × 1011 cm−2 at the SiC/AlN interface. The current–voltage (I–V) data demonstrate SiC/AlN metal–insulator-semiconductor (MIS) capacitors achieving a breakdown field strength of 11.4 MV/cm and a barrier height of 1.64 eV based on the Fowler–Nordheim tunneling (F–N) fitting. The barrier height between SiC and AlN derived from the F–N tunneling aligns with the ΔEC calculated from XPS analysis, demonstrating the excellent blocking characteristics of AlN/SiC MIS structure. Overall, the proposed PEALD method looks advantageous for preparing AlN films with excellent dielectric properties for future advanced SiC metal–oxide–semiconductor (MOS) devices.