Crystalline SiNx ultrathin films grown on AlGaN/GaN using In situ metalorganic chemical vapor deposition

Surface passivation by SiN (x) films is indispensable for high-power operation of AlGaN/GaN heterojunction field-effect transistors (HFETs) since it can effectively suppress collapse in the drain current. So far, the plasma-enhanced chemical vapor deposition technique has been used for the SiN (x) deposition; however, possible damage induced by the plasma processing may affect direct-current performance or reliability. In this paper, we present subsequent deposition of SiN (x) ultrathin films on AlGaN/GaN in the same metalorganic chemical vapor deposition reactor. It is experimentally found that this in situ SiN (x) passivation doubles the sheet carrier density at the AlGaN/GaN interface from that of the unpassivated sample. High-resolution cross-sectional transmission electron microscopy reveals that in situ SiN (x) is crystallized on the AlGaN layer as island-like structures via the Stranski-Krastanov growth mode. The lattice constants of in situ SiN (x) are estimated to be a approximate to 3.2 angstrom and c approximate to 2.4 angstrom, which are quite different from those of well-known Si3N4 crystal structures. First-principles calculation predicts that the crystal structure of in situ SiN (x) is the defect wurtzite structure, which well explains the experimental results. The passivation technique using crystalline SiN (x) films would be promising for high-power and high-frequency applications of AlGaN/GaN HFETs.