N. Achtziger

Band gap states of Ti, V, and Cr in 4H–silicon carbide

Band gap states of Ti, V, and Cr in n-type 4H–SiC were investigated by radiotracer deep level transient spectroscopy (DLTS). Doping with the radioactive isotopes 48V and 51Cr was done by recoil implantation followed by annealing (1600 K). Repeated DLTS measurements during the elemental transmutation of these isotopes to 48Ti and 51V, respectively, reveal the corresponding concentration changes of band gap states. Thus, six levels are identified in the band gap: Cr levels at 0.15, 0.18, and 0.74 eV, one V level at 0.97 eV, and two Ti levels at 0.13 and 0.17 eV below the conduction band edge.

Hydrogen passivation of silicon carbide by low-energy ion implantation

Ion implantation of deuterium is performed to investigate the mobility and passivating effect of hydrogen in epitaxial α-SiC (polytypes 4H and 6H). To avoid excessive damage and the resulting trapping of hydrogen, the implantation is performed with low energy (600 eV 2H2+). The 2H depth profile is analyzed by secondary ion mass spectrometry. Electrical properties are measured by capacitance–voltage profiling and admittance spectroscopy. In p-type SiC, hydrogen diffuses on a μm scale even at room temperature and effectively passivates acceptors. In n-type SiC, the incorporation of H is suppressed and no passivation is detected.

RECOIL IMPLANTATION OF RADIOACTIVE TRANSITION METALS AND THEIR INVESTIGATION IN SILICON BY DEEP-LEVEL TRANSIENT SPECTROSCOPY

Radioactive isotopes are produced by nuclear reactions in a thin target foil. The recoiling products are directly implanted into samples mounted off‐axis to the primary beam. Using proton or α beams and appropriate target foils, radioactive isotopes of Ti, V, Cr, Mn, and Co were implanted. The implantation parameters are presented and compared with other implantation techniques for radioactive isotopes. To demonstrate an application, a deep‐level transient spectroscopy measurement on 48V in silicon is presented. Ti and V correlated band‐gap levels were observed during the 48V decay.

Radiotracer investigation of deep Ga- and Zn-related band gap states in 6H–SiC

To identify Ga- or Zn-related deep levels, deep level transient spectroscopy (DLTS) measurements were performed repeatedly during the elemental transmutation of 67Ga to 67Zn. The radioactive isotope 67Ga was recoil implanted into p-type 6H–SiC for radiotracer experiments. The DLTS spectra exhibit one peak of time-dependent height. It describes the increasing concentration of the daughter element Zn with the half life of the nuclear decay. Thus, one Zn-related level at 1.16 eV above the valence band edge is definitely identified. There is no deep level of Ga in the lower part of the band gap.

Deep levels of tantalum in silicon carbide and incorporation during crystal growth

Band-gap states of tantalum in n-type 6H– and 15R–silicon carbide (SiC) were investigated by deep-level transient spectroscopy (DLTS). The samples were doped with Ta by ion implantation followed by an annealing procedure. DLTS measurements reveal two implantation-induced band-gap states in each polytype. These donor-like levels (located at EC−0.46 eV and EC−0.49 eV in 6H– and EC−0.43 eV and EC−0.46 eV in 15R–SiC) are assigned to Ta occupying inequivalent lattice sites in the SiC crystals. The investigation of 6H–SiC bulk material grown in an atmosphere containing Ta indicates the incorporation of Ta in these crystals during growth.