J. Pascual

Low-doped 6H-SiC n-type epilayers grown by sublimation epitaxy

Abstract Sublimation epitaxy has not yet been a technique of prime importance to grow epitaxial 6H-SiC layers because grown layers have always shown a residual net doping level higher than 10 16 cm −3 and a high compensation level. We present here results obtained with an optimized technology of sublimation epitaxial growth, which can be used to obtain structurally perfect layers with a concentration of uncompensated donors as low as 10 15 cm −3 . These layers have been both physically and electrically characterized. Deep level transient spectroscopy indicates that the concentration of deep levels is greatly reduced. As a consequence the hole diffusion length is significantly increased up to about 2.5 μm, as confirmed by electron beam induced current measurements. So these optimized layers are envisaged for the fabrication of high voltage diodes or bipolar transistors.

Structural, optical and electrical properties of state of the art cubic SiC films

Abstract The structural, optical and electrical characteristics of commercially available cubic (β)-SiC films grown on 〈001〉 silicon waters were reported. For the structural characterization, combined plane view and cross-section transmission electron spectroscopy observations were made. For the optical investigations, low-temperature photoluminescence (2 K) and room temperature Raman and infrared spectra were measured. For the electrical characterization, Hall effect and resistivity measurements were performed in the temperature range 15–500 K.

Electrical characterization of SiC for high-temperature thermal-sensor applications

Abstract The chemical and physical characteristics of silicon carbide (SiC) films make them increasingly interesting for sensors and devices operating at high temperature, high pressure and/or in aggressive environments. Concerning thermal sensors, for instance, it is well known that in many cases they have to work in perturbed environments where temperature and pressure are not independent constraints. As a consequence, it is necessary to know independently the sensitivity of a given sensor to both of them in order to design a specific application. This is done in this work for cubic β-SiC. Investigating both the temperature and hydrostatic pressure dependence of the transport properties in a series of thin films deposited on 〈100〉 Si substrates, we find that the hydrostatic pressure dependence is negligibly small (a few ppm bar −1 ) with respect to the temperature sensitivity (10 3 ppm °C −1 ).

Optical study of boron nitride thin films prepared by plasma-enhanced chemical vapor deposition

Abstract We investigate the effects of finite off-normal incidence on the polarized infrared reflectivity spectra of hexagonal boron nitride films deposited on Si substrates by radio frequency plasma enhanced chemical vapor deposition, using B 2 H 6 (1% in H 2 ) and NH 3 gases. The experimental observation of a sharp structure associated to the coupling of the incident light with the LO component of the twofold stretching mode, and the absence of similar coupling effects with the LO component of the bending mode, indicates that the c -axis is parallel to the film surface. We also show that the infrared spectra are not modified when one rotates the sample perpendicularly to the growth direction. Therefore, we conclude that the principal axis of the polycrystalline boron nitride films is randomly oriented within the plane parallel to the film surface. Finally, we show that these optical results are in full agreement with high resolution transmission electron microscopy studies.

Optimisation of junction termination extension for the development of a 2000 V planar 4H-SiC diode

Abstract The device structure of a 2 kV 4H–SiC P+NN+ planar diode with different edge terminations is optimised with simulation results. Since the periphery protection is a key issue in the design of Silicon carbide (SiC) power diodes, several techniques such as single- and double-junction termination extension (JTE) and a combination of JTE and guard rings (GRs) have been studied. The MEDICI simulator has been used, including specific parameters for 4H–SiC. In the single implanted zone JTE, the breakdown is strongly dependent upon the dose of dopants introduced into the edge region. We find that a depletion of the surface doping effectively reduces the surface electric field up to 40%. To widen the range of optimum JTE parameters keeping technological simplicity in mind, we have studied the behaviour of double JTE structures. Another investigated periphery protection, consist to form a series of GRs embedded in a JTE structure, with this protection the diode achieves more ideal efficiency of breakdown capabilities.

Gas source molecular beam epitaxy of β-SiC on Si substrates

The growth of β-SiC films on Si(100) substrates using C 2 H 2 gas and Si solid sources in a molecular beam epitaxy system has been investigated. Different C 2 H 2 and Si fluxes as well as different substrate temperatures have been used. The growth was performed at two steps : the initial optimal carbonisation step followed by the MBE growth with simultaneous supply of Si molecular and C 2 H 2 gas beams. The films were analysed using reflected high-energy electron diffraction, scanning electron microscopy, transmission electron microscopy, atomic force microscopy and Fourier transform infrared spectroscopy. Thin (< 0.1 μm) single crystalline SiC was grown at 980°C while 850°C was sufficient for the carbonisation of the Si surface. Films thicker than 0.1 μm are partially polycrystalline.

Lateral spread of implanted ion distributions in 6HSiC: simulation

In this paper, Monte Carlo simulation, using improved models for electronic stopping and 3D damage accumulation has been carried out to calculate the lateral distribution of ions implanted into 6HSiC crystal. Two dimensional concentration contour plots are used to show the lateral spread of implanted Al+ ions at mask edges. It appears that channeling strongly influences the shape of lateral distributions due to the capture of random implanted ions by axial channels lying parallel to the (0001) surface of 6HSiC which appears alternatively every 30° around the 〈0001〉 axis, according to the symmetry of the 6HSiC crystal. This phenomenon, if confirmed by SIMS 2D profiling, could have important consequences on the behavior of ion implanted lateral junctions of SiC devices.

INFRARED AND RAMAN ANALYSIS OF PLASMA CVD BORON NITRIDE THIN FILMS

We present an optical investigation, by means of polarized IR reflectivity and Raman scattering, of the quality and stability of PECVD grown BN films obtained on the anode and on the cathode of a parallel-plate radio-frequency reactor by glow discharge decomposition of two different gas mixtures, B2H6-H2-NH3 and B2H6-N2. The addition of Ar to B2H6-N2 has also been investigated. It is shown that polarized IR reflection spectra of thin films have a complex optical behaviour, which is a function of the oblique angle of incidence and the substrate material used in the deposit. However, these spectra are predictable when optical theory is applied. The results obtained show the capabilities of polarized IR reflection and Raman scattering to perform detailed investigations on the microstructure and aging of BN thin films, independently of the substrate material.

Optical tools for intermixing diagnostic: application to InGaAs/InGaAsP microstructures

Abstract InGaAs quantum wells (QWs), with either InP or InGaAsP barriers, are increasingly considered for optoelectronic device applications. Nevertheless, because interdiffusion across the interfaces (intermixing) results in unwanted modifications of the nominal properties, in-situ controls of the well composition (to be ultimately done during the processing sequences) are of fundamental interest. In this work, we have used a single quantum well of InGaAs/InGaAsP as a prototype structure and we investigate the respective advantage (and/or disadvantage) of both PL and Raman tools as non-destructive techniques. Provided careful analyses are done, we find that both determinations are in satisfactory agreement and constitute alternative but non-equivalent techniques for in-line characterization.

SiC Base Micro-Probe for Myocardial Ischemia Monitoring

This paper describes the development, fabrication, packaging and mechanical characterization of a SiC based microprobe for myocardial ischemia monitoring during cardiac artificial arrest. The packaged microprobe has two SiC needles. One needle monitors the tissue impedance and the other controls the temperature. Both needles have been assembled on a ceramic substrate and packaged in epoxy resin. Mechanical characterization of the needles and the system as well have been performed. Yielding force measurements and insertion tests in heart tissue show that SiC-based needles have better mechanical properties than Si needles of the same length but with double the cross section area.