Deep levels of vacancy-hydrogen centers in silicon studied by Laplace DLTS

We identify the acceptor levels (-/0) of the VH and V2H defects in silicon from comparison of DLTS and EPR annealing data. The levels are very close t o each other and close to the acceptor level of the PV defect (the E-center ) as well. In order to separate them, we have applied the high-resolution t echnique of Laplace DLTS and compared the formation and annealing propertie s of defects generated by implantation of hydrogen or helium. We further ap plied Laplace DLTS in combination with uniaxial stress to study the accepto r level at E-c - E-t = 0.31 eV previously assigned to a vacancy-hydrogen-ox ygen defect. We find, in accordance with recent EPR measurements, that the defect displays orthorhombic-I symmetry and rule out that it contains two h ydrogen atoms. The defect can be understood as a single hydrogen atom bound inside the A-center, the well-known VO defect of silicon, and we denote it VOH accordingly. The observed orthorhombic-I symmetry arises because the h ydrogen atom (at T = 160 K) swiftly jumps among two equivalent sites across the(1 1 0) plane that contains the Si-O-Si bond. Previous studies have sho wn that hydrogenation of oxygen-rich electron-irradiated samples leads to t he formation of VOH with simultaneous depletion of the A-center. Our struct ural data are in accordance with this dynamic behavior. (C) 1999 Elsevier S cience B.V. All rights reserved.