Anne Henry

Deep levels created by low energy electron irradiation in 4H-SiC

With low energy electron irradiation in the 80–250keV range, we were able to create only those intrinsic defects related to the initial displacements of carbon atoms in the silicon carbide lattice. Radiation induced majority and minority carrier traps were analyzed using capacitance transient techniques. Four electron traps (EH1, Z1∕Z2, EH3, and EH7) and one hole trap (HS2) were detected in the measured temperature range. Their concentrations show linear increase with the irradiation dose, indicating that no divacancies or di-interstitials are generated. None of the observed defects was found to be an intrinsic defect–impurity complex. The energy dependence of the defect introduction rates and annealing behavior are presented and possible microscopic models for the defects are discussed. No further defects were detected for electron energies above the previously assigned threshold for the displacement of the silicon atom at 250keV.

Influence of epitaxial growth and substrate-induced defects on the breakdown of 4H-SiC Schottky diodes

Morphological defects and elementary screw dislocations in 4H-SiC were studied by high voltage Ni Schottky diodes. Micropipes were found to severely limit the performance of 4H-SiC power devices, w ...

PHOTOLUMINESCENCE STUDIES OF POROUS SILICON CARBIDE

A detailed investigation of the dependence of the photoluminescence from porous silicon carbide on preparation conditions and starting material is presented. Porous silicon carbide prepared from different polytypes shows almost identical emission spectra, demonstrating a clear impedance of the band‐gap energy of a particular SiC polytype. Emission bands with peak energies of 2.43, 2.22, 2.07, and 1.93 eV were resolved with the use of selective excitation by tuning the excitation wavelength. The origin of luminescence is suggested to relate to defect states produced at the etched surface.

A 4.5 kV 6H silicon carbide rectifier

Reactive ion etched silicon carbide mesa pin diodes with voltage blocking capabilities as high as 4.5 kV have been fabricated from 6H–SiC epitaxial layers. The epitaxial structure was grown by chemical vapor deposition on an n+ substrate giving a low‐doped 45 μm thick n− active base layer and a 1.5 μm thick high‐doped p+ emitter layer on top. A high minority carrier lifetime of 0.43 μs in the n− active base layer provides good on‐state properties with a typical forward voltage drop of 6 V at 100 A/cm2.

Growth of SiC by "Hot-Wall" CVD and HTCVD

A reactor concept for the growth of high-quality epitaxial SiC films has been investigated. The reactor concept is based on a hot-wall type susceptor which, due to the unique design, is very power efficient. Four different susceptors are discussed in terms of quality and uniformity of the grown material. The films are grown using the silane–propane–hydrogen system on off-axis (0001) 6H- and 4H-SiC substrates. Layers with doping levels in the low 1014 cm—3 showing strong free exciton emission in the photoluminescence spectra may readily be grown reproducibly in this system. The quality of the grown layers is also confirmed by the room temperature minority carrier lifetimes in the microsecond range and the optically detected cyclotron resonance data which give mobilities in excess of 100000 cm2/Vs at 6 K. Finally, a brief description will be given of the HTCVD technique which shows promising results in terms of high quality material grown at high growth rates.

High temperature chemical vapor deposition of SiC

A growth process has been investigated for the epitaxial growth of silicon carbide. The technique can simply be described as chemical vapor deposition (CVD) at high temperatures, hence the name high temperature CVD (HTCVD). The growth process however, differs greatly from that of the CVD process due to the significant sublimation and etch rates at the extreme growth temperatures (1800–2300°C). The grown rates obtained with the HTCVD are in the order of several tens of μm/h to 0.5 mm/h. The purity and crystallinity of the growth layers are outstanding showing strong free exciton related photoluminescence.

Nitrogen doping concentration as determined by photoluminescence in 4H– and 6H–SiC

Low‐temperature photoluminescence (PL) spectroscopy is used for determination of the nitrogen doping concentration in noncompensated 4H– and 6H–SiC by comparing the intensity of nitrogen‐bound exciton (BE) lines to that of the free exciton (FE), the latter being used as an internal reference. The results are compared with a previous work performed for the case of 6H–SiC only. A line‐fitting procedure with the proper line shapes is used to determine the contribution of the BE and FE lines in the PL spectrum. The ratio of the BE zero‐phonon lines (R0 and S0 in 6H, Q0 in 4H) to the FE most intensive phonon replica around 77 meV exhibits very well a direct proportional dependence on the doping as determined by capacitance–voltage (C–V) measurements for both polytypes. The use of fitting procedure which takes into account the real line shapes, the influence of the spectrometer transfer function, and the structure of the PL spectrum in the vicinity of the FE replica allows us determination of the N‐doping conce...

Single-Molecule Chemistry with Surface- and Tip-Enhanced Raman Spectroscopy

Single-molecule (SM) surface-enhanced Raman spectroscopy (SERS) and tip-enhanced Raman spectroscopy (TERS) have emerged as analytical techniques for characterizing molecular systems in nanoscale environments. SERS and TERS use plasmonically enhanced Raman scattering to characterize the chemical information on single molecules. Additionally, TERS can image single molecules with subnanometer spatial resolution. In this review, we cover the development and history of SERS and TERS, including the concept of SERS hot spots and the plasmonic nanostructures necessary for SM detection, the past and current methodologies for verifying SMSERS, and investigations into understanding the signal heterogeneities observed with SMSERS. Moving on to TERS, we cover tip fabrication and the physical origins of the subnanometer spatial resolution. Then, we highlight recent advances of SMSERS and TERS in fields such as electrochemistry, catalysis, and SM electronics, which all benefit from the vibrational characterization of single molecules. SMSERS and TERS provide new insights on molecular behavior that would otherwise be obscured in an ensemble-averaged measurement.

Pseudodonor nature of the DI defect in 4H-SiC

We use the recent findings about the pseudodonor character of the DI defect to establish an energy-level scheme in the band gap for the defect, predicting the existence of a hole trap at about 0.35 eV above the valence band. Using minority carrier transient spectroscopy, we prove that the DI defect indeed is correlated to such a hole trap. In addition, we show that the DI defect is not correlated to the Z1/2 electron trap, in contrast to what was previously reported.

Growth rate predictions of chemical vapor deposited silicon carbide epitaxial layers

Abstract Complete 3D simulations of a silicon carbide chemical vapor deposition (CVD) reactor, including inductive heating and fluid dynamics as well as gas phase and surface chemistry, have been performed. For the validation of simulated results, growth was conducted in a horizontal hot-wall CVD reactor operating at 1600°C, using SiH4 and C3H8 as precursor gases. Simulations were performed for an experimental hot-wall CVD reactor, but the results are applicable to any reactor configuration since no adjustable parameters were used to fit experimental data. The simulated results obtained are in very good agreement with experimental values. It is shown that including etching and parasitic growth on all reactor walls exposed to the gas greatly improves the accuracy of the simulations.