Hervé Peyre

Investigation of 2 inch SiC layers grown in a resistively-heated LP-CVD reactor with horizontal “hot-walls”

With respect to more standard and more widely used inductive-heating, the resistivelyheated reactors offer the strong advantage of low cost, easy installation and low running constraints. Combined with an easy adaptation to the increasing size of wafers, this results in very strong advantages. This simple technique was mainly restricted to the growth of small size samples for academic purpose [1]. In this work we report an investigation of 2 inch SiC layers deposited in a new, horizontal and resistively-heated, “hot-wall” LP-CVD reactor specially designed for large flexibility. Introduction Due to superior physical properties, SiC appears as a most promising material for high power, high frequency and high temperature electronic devices or sensors. In this case, whatever is the targeted application, one needs to deposit a low doped, electronic grade material, on a large diameter single crystalline wafer. A promising technique is the use of hot-wall CVD, coupled with resistive heaters. With respect to the more standard and widely used inductive-heating technology, a resistivelyheated reactor offers advantages in terms of (low) cost, (easy) installation and (low) running constraints. Combined with a very easy adaptation to the increasing size of wafers, this seems very appealing. Unfortunately, up to now, this simple technique has been restricted to the growth of small size samples for academic purpose [1] and was not seriously considered for industrial applications. In order to establish more the potentiality of this system, we report a detailed investigation of the thickness uniformity, surface morphology and low temperature photoluminescence properties of a series of epitaxial layers deposited on silicon. We show that, on 2” Si substrates, state of the art material can be easily obtained. Experimental The reactor has been specially designed to allow, both, usual SiC growth by LP-CVD [1] as well as full Si-wafer conversion by LPE [2]. In this case, the control of the vertical temperature gradient is essential to insure an optimised liquid phase diffusion. This technical constraint dictated the choice of two independent heaters (upper and lower resistive) forming then a standard“hot-walls” configuration. The walls are thin (0.5mm) and made of high purity graphite sheets. The thermal inertia is then very low, which allows RTP (Rapid Thermal Processing) to be done up to 1800°C. In order to Materials Science Forum Online: 2004-06-15 ISSN: 1662-9752, Vols. 457-460, pp 273-276 doi:10.4028/www.scientific.net/MSF.457-460.273

Hexamethyldisilane/propane versus silane/propane precursors: application to the growth of high-quality 3C–SiC on Si

From a comparative evaluation of hexamethyldisilane (HMDS) and silane–propane (SP) precursor systems, it is shown that HMDS needs a small addition of propane to deposit heteroepitaxial layers of 3C–SiC on Si with superior crystalline properties. In this case, propane compensates for the secondary reactions induced by hydrogen reacting with carbon. Using atmospheric pressure chemical vapour deposition conditions, the new system (HMDS–propane) demonstrates several advantages. It is safer to handle than SP and allows a higher growth rate (up to 7 µm h−1 at 1350 °C) without any degradation of the layer morphology. However, when lowering the deposition temperature, HMDS is revealed to be more stable than silane. This is in contrast to most standard beliefs but explains why a high temperature (~1350 °C) is always necessary to grow high-quality material using HMDS.

Combined effects of Ga, N, and Al codoping in solution grown 3C–SiC

We report on Ga-doped 3C–SiC epitaxial layers grown on on-axis (0001) 6H–SiC substrates using the vapor-liquid-solid technique and different Si1−xGax melts. The resulting samples have been investigated using secondary ion mass spectroscopy (SIMS), micro-Raman spectroscopy (μ-R) and, finally, low temperature photoluminescence (LTPL) spectroscopy. From SIMS measurements we find Ga concentrations in the range of 1018 cm−3, systematically accompanied by high nitrogen content. In good agreement with these findings, the μ-R spectra show that the Ga-doped samples are n-type, with electron concentrations close to 2×1018 cm−3. As expected, the LTPL spectra are dominated by strong N–Ga donor-acceptor pair (DAP) transitions. In one sample, a weak additional N–Al DAP recombination spectrum is also observed, showing the possibility to have accidental codoping with Ga and Al simultaneously. This was confirmed on a non-intentionally doped 3C–SiC (witness) sample on which, apart of the usual N and Al bound exciton lines,...

Trends in Dopant Incorporation for 3C-SiC Films on Silicon

We have investigated the influence of several growth parameters on the incorporation of doping species in the case of 3C-SiC layers grown by CVD on silicon. This includes nitrogen (both intentional and residual) as well as residual aluminum. All concentrations have been determined by SIMS (Secondary Ion Mass Spectrometry). First, we investigated the effect of the growth temperature, growth rate and C/Si ratio on the doping level of (100) oriented layers. Then, we compared the change in nitrogen incorporation versus nitrogen flow rate for layers grown on (100), (111), (110) and (211) oriented wafers.

p-Type Doping of 4H- and 3C-SiC Epitaxial Layers with Aluminum

Exhaustive experimental study of aluminum incorporation in epitaxial 4H-SiC and 3C‑SiC films grown by chemical vapor deposition (CVD) was performed. The influence of polytype and substrate orientation was verified. Role of principal process conditions (growth temperature and pressure, deposition rate, chemical environment) was investigated in details. Finally, the evolution of optical properties of resulting SiC films with Al content was examined.

Fluorescent silicon carbide as an ultraviolet-to-visible light converter by control of donor to acceptor recombinations

As an alternative to the conventional phosphors in white LEDs, a donor and acceptor co-doped fluorescent 6H-SiC can be used as an ultraviolet-to-visible light converter without any need of rare-earth metals. From experimental data we provide an explanation to how light can be obtained at room temperature by a balance of the donors and acceptors. A steady-state recombination rate model is used to demonstrate that the luminescence in fluorescent SiC can be enhanced by controlling the donor and acceptor doping levels. A doping criterion for optimization of this luminescence is thus proposed.

Modelling of 4H-SiC VJFETs with Self-Aligned Contacts

Purely vertical 4H-SiC JFETs have been modeled by using three different approaches: the analytical model, the finite element model and the compact model. The results of the modeling have been compared with experimental results on a series of fabricated self-aligned devices with two different channel lengths (0.3 and 1.1μm) and various channel widths (1.5, 2, 2.5, 3, 4 and 5 μm). For all the considered models I-V and C-V characteristics could be satisfactorily simulated.

LTPL Investigation of N-Ga and N-Al Donor-Acceptor Pair Spectra in 3C-SiC Layers Grown by VLS on 6H-SiC Substrates

Ga-doped 3C-SiC layers have been grown on on-axis 6H-SiC (0001) substrates by the VLS technique and investigated by low temperature photoluminescence (LTPL) measurements. On these Ga-doped samples, all experimental spectra collected at 5K were found dominated by strong N-Ga donor-acceptor pair (DAP) transitions and phonon replicas. As expected, the N-Ga DAP zero-phonon line (ZPL) was located at lower energy (~ 86 meV) below the N-Al one. Fitting the transition energies for the N-Al close DAP lines gave 251 meV for the Al acceptor binding energy in 3C-SiC and, by comparison, 337 meV for the Ga acceptor one.

Growth and Characterization of 13C Enriched 4H-SiC for Fundamental Materials Studies

We have carried out the growth and basic characterization of isotopically enriched 4HSi 13C crystals. In recent years the growth of 13C enriched 6H-SiC has been performed in order to carry out fundamental materials studies (e.g. determination of phonon energies, fundamental bandgap shift, carbon interstitial defect study, analysis of the physical vapor transport (PVT) growth process). For electronic device applications, however, the 4H-SiC polytype is the favored material, because it offers greater electron mobility. In this paper we present the growth of 4H-Si13C single crystals with up to 60% of 13C concentration. From a physical point of view we present first results on phonons as well as the fundamental bandgap energy shift due to 13C incorporation into the SiC lattice.

Electrical Transport Properties of Highly Aluminum Doped p-Type 4H-SiC

In the range 80 K-900 K, we have investigated the electrical properties of heavily aluminum in-situ doped, 4H-SiC samples. The temperature dependence of the hole concentration and Hall mobility was analyzed in the model taking into account heavy and light holes. The modelisation parameters were compared with experimental values of Secondary Ion Mass Spectroscopy (SIMS) and Capacitance-Voltage (CV) measurements.