M. Schulz

Intrinsic SiC/SiO2 Interface States

The energy distribution of electron states at SiC/SiO 2 interfaces produced by oxidation of various (3C, 4H, 6H) SiC polytypes is studied by electrical analysis techniques and internal photoemission spectroscopy. A similar distribution of interface traps over the SiC bandgap is observed for different polytypes indicating a common nature of interfacial defects. Carbon clusters at the SiC/SiO 2 interface and near-interfacial defects in the SiO 2 are proposed to be responsible for the dominant portion of interface traps, while contributions caused by dopant-related defects and dangling bonds at the SiC surface are not observed.

Random telegraph signal: An atomic probe of the local current in field-effect transistors

The switching amplitude of random telegraph signals (RTSs) caused by trapping a single electron at an individual interface defect is studied in sub-μm-sized metal oxide field-effect transistors (MOSFETs). The amplitudes of RTSs depend on the channel nonuniformity and, in particular, on the current distribution in the immediate vicinity of the trap. We find that to a good approximation the RTS amplitude is proportional to the square of the local current density. This mathematical relation is tested and verified with the help of a computer simulation. RTS amplitudes may thus be used as atomic probes of the local current density. By the evaluation of 187 RTS amplitudes in different MOSFETs of the same type, we deduce for the first time a histogram showing the magnitude distribution of the local current density in such devices.

Conductance modulation of submicrometer metal–oxide–semiconductor field‐effect transistors by single‐electron trapping

The capture and emission of electrons at single, individual interface traps is studied in sub‐μm metal–oxide–semiconductor field‐effect transistors (MOSFETs) by the random telegraph signals (RTSs) they induce by source‐drain conductance modulations. The magnitude of the RTSs observed frequently exceeds 10% of the channel conductance and it exhibits a large scatter over two orders of magnitude. Analytical estimates and computer modeling show that the magnitude of the RTSs and the scatter cannot occur for a uniform MOSFET channel. It is concluded that fixed oxide and interface charge centers, which are present in the active device area at a high concentration, cause a percolating current distribution in the channel. The lucky trap centers located close to current paths give rise to large RTSs. The scatter in the magnitude of the RTSs is due to the random location of traps in the percolation pattern. Trapping centers causing RTSs thus act as atomic probes of the nonuniform current distribution in the channel.

Evaluation of the Coulomb energy for single‐electron interface trapping in sub‐μm metal‐oxide‐semiconductor field‐effect transistors

Capture and emission time constants are measured for a set of individual interface traps in different metal‐oxide‐semiconductor field‐effect transistors (MOSFETs) by random telegraph signals. The data are evaluated to extract the Coulomb energy induced by the transfer of a single electron into an interface trap. A unified Coulomb energy of the order of several hundred millivolts independent of trap‐specific properties is found, which is proportional to temperature and decays logarithmically with inversion carrier density in the MOSFET channel. The Coulomb energy found is in quantitative agreement with the theoretical modeling. The Coulomb effect is large compared to the trap lowering by the electric field and to the residual entropy change.

Degradation of 6H-SiC MOS capacitors operated at high temperatures

Abstract 6HSiC MOS capacitors were operated at temperatures above 600K under negative bias. Enhancement of energetically shallow and deep interface states at n/p-type SiC SiO 2 structures and of a fixed charge are observed, which can partially be passivated by a hydrogen treatment. The generation and passivation of the fixed charge is explained in the framework of the “negative-bias-temperature instability” originally proposed for Si-based MOS capacitors.

Charge trapping and interface state generation in 6H-SiC MOS structures

Abstract Comparative studies of the oxide charge trapping and interface state generation in n-6HSiC SiO 2 and Si SiO 2 structures were performed using electron/hole photo-injection. The thermal oxide on SiC was found to have a comparable density of electron traps and even lower density of hole traps than that one on Si. In contrast to the Si SiO 2 system, the electron injection in the oxide on 6HSiC produces a large density of deep acceptor interface states, which are stable in the temperature range below 300 °C.

Conductance modulation by single-electron trapping in sub-mMOSFETs

Abstract The discrete conductance modulations induced by single-electron trapping in sub-μm MOSFETs frequently exceed 10% of the channel conductance and exhibit a large scatter up to two orders of magnitude. It is shown by computer modeling that these modulation properties can only be caused by a spatial non-uniformity of the channel due to fixed oxide charges. In this work the effect of fixed interface charge, which also spatially modulates the channel conductivity, is investigated in detail.

Coulomb free energy for single-electron interface trapping in sub-mm MOSFETs

Abstract Capture and emission time constants are measured for various individual traps by random telegraph signals. The data is quantitatively described by taking into account a change in Coulomb free energy common to all the traps in addition to the binding energy specific for each trap.

Resistivity of Ultrathin (0.6–3.7 nm) IrSi Films on Si(100)

Ultrathin (0.6-3.7 nm) IrSi films are fabricated by electron beam evaporation of iridium metal onto n-type silicon (100) substrates and subsequent silicide formation at 500°C. The sheet resistivity is measured at various temperatures in the range from 15 to 300 K. The polycrystalline c-IrSi films which form for a film thickness in excess of 8 nm show a metal-like behaviour of the resistivity. Ultrathin IrSi films of thickness less than 4 nm show an anomalous resistivity that increases with decreasing temperature. The exponential law observed for the resistivity is found to be consistent with hopping transport in amorphous IrSi predicted by the structure analysis for the thin films.

Infrared Optical Properties of Iridium Silicides

Amorphous (a-Irsi) and crystalline (c-IrSi, Ir 3 Si 4 ) iridium silicide layers (1 to 80 nm) are fabricated by evaporation of iridium metal onto Si(1000) substrates and subsequent annealing at various temperatures in the range from 440 to 530°C. The infrared transmission and reflection are measured for the layer system as a function of the wavelength in the range from 2 to 6 μm and as a function of the film thickness. The dielectric permittivity of the silicide films is determined by taking into account multiple reflections in the thin film. All the silicides investigated show metallic behavior. The crystalline iridium silicide phases c-IrSi and Ir 3 Si 4 are well described by the Drude model; the amorphous a-IrSi exhibits a reduced absorption indicating a reduced density of states near the Fermi energy.