The epitaxial crystalline silicon-oxynitride layer on SiC(0001): Formation of an ideal SiC-insulator interface

摘要

Silicon carbide (SiC) has the potential to serve as an extremely important semiconductor material in next-generation electronics. However, a major stumbling block for its practical application has been the preparation of high-quality interfaces with insulating materials. We have discovered a way to prepare a 0.6-nm thick silicon oxynitride (SiON) layer having an epitaxial interface with the SiC(0001) surface. This review article focuses on the atomic and electronic structures of the SiON layer. Based on various experimental techniques and theoretical studies, we understand the SiON layer to be a complex but unique hetero-double-layered structure: a topmost Si_2O_5 monolayer is connected to an interfacial Si_2N_3 monolayer via Si-O-Si linear bridge bonds. The most striking feature of the SiON structure is that there is no dangling bond in the unit cell, rendering it remarkably robust to air exposure. Stability and processes for the formation of the SiON on SiC(0001) are discussed on the basis of the structural features obtained. Scanning tunneling spectroscopy measurements of the SiON exhibit a bulk SiO_2-like band gap of ～9 eV as well as first-principles calculations. The remarkable band-gap opening of such a thin insulator film is investigated by the combination of element-specific soft x-ray absorption/emission spectroscopies and by first-principles calculations, revealing the Si_2N_3 and Si_2O_5 monolayers to have band gaps.