Papers by Author: Hans Jürgen von Bardeleben

Abstract: In this work we elucidate the microscopic origin of the dominant radiation induced I-II spectra in p-type doped 4H-SiC. By calculating the electronic g-tensor from first principles in the framework of density functional theory, basal antisite pairs SiCCSi + are shown to give rise to the characteristic anisotropic g-tensors found in the electron paramagnetic resonance (EPR) measurements. Additional central hyperfine (hf) splittings of about 100 MHz due to the SiC antisite nuclei are predicted theoretically and also resolved experimentally. We have, thus, identified antisite pairs as a dominant defect in electron and proton irradiated p-type doped 4H-SiC.

Abstract: Previous Electron Paramagnetic Resonance (EPR) studies identified the carbon dangling bond center as the main paramagnetic interface defect in 3C, 4H, 6H-SiC/SiO2. We demonstrate that this defect, called PbC center, can be passivated by forming gas annealing at 400°C. We have measured the PbC density at annealed 4H- and 3C-SiC/SiO2 interfaces and attributed its reduction to the transformation of the dangling bonds into EPR inactive C-H bonds. We have also studied the reverse phenomenon occurring during vacuum annealing at temperatures ranging from 600°C up to 1000°C and have determined a dissociation energy of ≈4.3 eV for the 3C and 4H polytypes.

Abstract: Several 4H SiC samples have been electron-irradiated at near threshold energies at low fluence, either along the [0001] or [000-1] direction. PL and EPR techniques have been used to investigate the dependence of the beam direction on defect generation and, together with a sample irradiated at a higher fluence, to correlate differences brought about by irradiating with a change in electron fluence. Attempts are made to correlate the information derived from the two techniques.

Abstract: 6H-SiC single crystalline substrates were implanted at room temperature with 2 MeV Al2+ ions to fluences from 2×1014 Al2+ cm-2 to 7×1014 Al2+ cm-2 and with different current densities (from 6.6 to 33×1010 Al2+ cm-2 s-1). The depth profile of the damage induced by the Al2+ ions was determined by Backscattering Spectrometry in channeling geometry (BS/C) with a 3.5 MeV He2+ beam. The BS/C spectra were evaluated using the RBX code. The samples were subsequently annealed at 1100°C in N2 for one hour, in order to analyze their structural recovery by BS/C and the amount of the remaining defects by means of Electron Paramagnetic Resonance (EPR). The results from the BS/C spectra corresponding to the as-implanted samples indicate that the damage depends strongly on the total fluence but also, although to a lesser extent, on the beam current density. The BS/C measurements reveal that all the samples, except the one implanted with the highest fluence, recover completely their original crystalline structure after the annealing. Furthermore the angular anisotropy of the EPR spectra indicates that the implanted region recovered a good crystallinity, although some residual defects were observed.

Abstract: The effect of thermal treatments in nitric oxide (NO) on the paramagnetic defects at the 4H-SiC/SiO2 interface are analyzed by EPR in oxidized porous samples. The results on ultrathin thermal oxides show that the NO treatment at 1000°C is insufficient for an efficient reduction of the two dominant paramagnetic interface defects: PbC centers and carbon clusters. From the NRA and XPS analysis of bulk samples treated under the same conditions we attribute the weak effect to the low nitrogen concentration of only 1% at the interface.

Abstract: The defects at the 3C-SiC/SiO2 interface have been studied by X-band EPR spectroscopy in oxidized porous 3C-SiC. One interface defect is detected; its spin Hamiltonian parameters, spin S=1/2, C3V symmetry, g//=2.00238 and g⊥=2.00317, central hyperfine interaction (CHF) with one carbon atom and AB//[001]=48G and superhyperfine (SHF) interaction with three equivalent Si neighbour atoms and TB//[001]=12.4G, allow us to attribute the center to a sp3 coordinated carbon dangling bond center, PbC.