Eléna Bedel-Pereira

Comparative Study of Electrical and Microstructural Properties of 4H-SiC MOSFETs

N-channel MOSFETs were manufactured on p-type and on p-implanted, n-type 4H-SiC substrates. The electron mobility in the inversion channel was measured to be correlated with the structural and chemical properties determined by transmission electron microscopy. With regard to what was previously discussed in the literature, interfacial layer formation and carbon distribution across the SiC/SiO2 interface were considered in relation with the measured Hall electron mobility.

Influence of boron-interstitials clusters on hole mobility degradation in high dose boron-implanted ultrashallow junctions

Hole mobility degradation has been studied in high-dose boron-implanted ultrashallow junctions containing high concentrations of boron-interstitial clusters (BICs), combining an empirical method based on the self-consistent interpretation of secondary-ion-mass spectrometry (SIMS) and Hall measurements and liquid-nitrogen (LN2) to room temperature (RT) hole mobility measurements. It has been found that BICs act as independent scattering centers which have a strong impact on hole mobility in addition to the other scattering mechanisms such as lattice and impurities scattering. A mobility degradation coefficient α has been introduced, which gives information on the mobility degradation level in the analyzed junctions. In the case of very high concentrations of BICs (containing a boron density up to 8×1014 cm−2), measured hole mobilities were found to be ∼40% lower than corresponding theoretical values. BICs dissolution through multiple Flash anneals at high temperature (1300 °C) reduces the observe mobility ...

Impact of boron-interstitial clusters on Hall scattering factor in high-dose boron-implanted ultrashallow junctions

The Hall scattering factor rH has been determined for holes in high-dose boron-implanted ultrashallow junctions containing high concentrations of boron-interstitial clusters (BICs), combining scanning capacitance microscopy, nanospreading resistance, Hall effect, and secondary ion mass spectroscopy measurements. A value of rH=0.74±0.1 has been found in reference defect-free fully activated junctions, in good agreement with the existing literature. In the case of junctions containing high concentrations of immobile and electrically inactive BICs, and independently of the implant or the annealing process, the rH value has been found to be equal to 0.95±0.1. The increase in the rH value is explained in terms of the additional scattering centers associated to the presence of high concentrations of BICs.

Impact of acceptor concentration on electrical properties and density of interface states of 4H-SiC n-metal-oxide-semiconductor field effect transistors studied by Hall effect

Silicon carbide n-type metal-oxide-semiconductor field effect transistors (MOSFETs) with different p-body acceptor concentrations were characterized by Hall effect. Normally OFF MOSFETs with good transfer characteristics and low threshold voltage were obtained with a peak mobility of ∼145 cm2 V−1 s−1 for the lowest acceptor concentration. The results are explained in terms of an increase of Coulomb scattering centers when increasing the background doping. These scattering centers are associated to fixed oxide and trapped interface charges. Additionally, the observed mobility improvement is not related to a decrease of the interface states density as a function of background doping.

Spin transport in benzofurane bithiophene based organic spin valves

In this paper we present spin transport in organic spin-valves using benzofurane bithiophene (BF3) as spacer layer between NiFe and Co ferromagnetic electrodes. The use of an AlO x buffer layer between the top electrode and the organic layer is discussed in terms of improvements of stacking topology, electrical transport and oxygen contamination of the BF3 layer. A study of magnetic hysteresis cycles evidences spin-valve behaviour. Transport properties are indicative of unshorted devices with non-linear I-V characteristics. Finally we report a magnetoresistance of 3% at 40 K and 10 mV in a sample with a 50 nm thick spacer layer, using an AlO x buffer layer.

Spin-polarized transport in NiFe/perylene-3,4,9,10-tetracarboxylate/Co organic spin valves

We have prepared organic spin valves based on the perylene derivative perylene-3,4,9,10-tetracarboxylate (PTCTE) with NiFe and Co ferromagnetic electrodes (with direct or off-axis sample configuration for the Co upper electrode deposition). Transmission electron miscroscopy is employed to study the stacking of the NiFe/PTCTE/Co vertical structures. Tunneling atomic force microscopy reveals that direct deposition of Co damages the PTCTE layer. Moreover, fluorescence and I-V studies of PTCTE evidence changes of the organic layer’s transport properties that are correlated with the deposition rate of PTCTE. Finally, we report up to 3% magnetoresistance at 10 mV and 5 K on a sample with an organic spacer 300 nm in thickness and an off-axis deposited cobalt counter electrode. We analyze this result in terms of spin diffusion and spin precession in PTCTE.

Systematic Analysis of the High- and Low-Field Channel Mobility in Lateral 4H-SiC MOSFETs

In this work, we investigate the impact of Al-implantation into n-MOSFET channel regions together with its p-doping concentration upon the mobility limiting scattering mechanisms in the channel. For this purpose, a study of the interface trap density, interface trapped charge density, field-effect mobility, and Hall mobility is carried out for normally-off n-MOSFETs with different doping profiles and concentrations in the channel region. The trend of the field-effect and the Hall mobility as well as the differences thereof will be discussed. Based on the determined mobilities in the range from 11.9 cm2/Vs to 92.4 cm2/Vs, it will be shown that for p-doping concentrations above 5·1016 cm-3 Coulomb scattering is the dominant scattering mechanism for both, low- and high-field mobility. In contrast, for p-doping concentrations below 5·1016, cm-3 further scattering mechanisms will be considered that may account for the observed mobility trend at high electric fields.

Impact of Fabrication Process on Electrical Properties and on Interfacial Density of States in 4H-SiC n-MOSFETs Studied by Hall Effect

In this work, electrical properties of lateral n-channel MOSFETs implanted with differentnitrogen doses in the channel region were measured by Hall-effect technique at 300K. A mobility improvement with increasing nitrogen implantation doses is observed. Interface trap density (Dit) was determined from the experimentally measured Hall carrier density. Our results show a high Dit near and within the conduction band that does not change significantly when the nitrogen implantation dose is increased, despite observed mobility improvement.

Hall Factor Calculation for the Characterization of Transport Properties in N-Channel 4H-SiC MOSFETs

For the characterization of n-channel 4H-SiC MOSFETs, current-voltage and Hall-effect measurements were carried out at room temperature. To interpret the Hall-effect measurements, the Hall factor for the electron transport in the channel of SiC MOSFETs was evaluated, for the first time. The method of the Hall factor calculation is based on the interdependence with mobility components via the respective scattering relaxation times. The results of the calculation reveal a strong dependence of the Hall factor on the gate voltage. Depending on the gate voltage applied, the values of the Hall factor vary between 1.3 and 1.5. Sheet carrier density and drift mobility values derived from the Hall-effect measurements using our new gate-voltage-dependent Hall factor show very good agreement with simulations performed with Sentaurus Device of Synopsys.

Nano-Analytical and Electrical Characterization of 4H-SiC MOSFETs

4H-SiC presents great advantages for its use in power electronic devices working at particular conditions. However the development of MOSFETs based on this material is limited by mobility degradation. N-channel SiC MOSFETs were manufactured on p-type epitaxial and p-implanted substrates and the electron mobility in the inversion channels was measured to be correlated with their structural and chemical properties determined by transmission electron microscopy methods. With regard to what was previously discussed in the literature, transition layer formation and carbon distribution across the SiC-SiO2 interface are considered in relation with the measured low electron mobility of the MOSFETS.