Search

Starting from the previously demonstrated twin-free 3C-SiC growth on 4H-SiC when using Ge pre-deposition treatment, this work focuses on the understanding of the growth mechanism that stands behind this result. Toward this end, short growth experiments were performed to allow the investigation of the nucleation stage. Based on the experimental observations, a mechanism is proposed which involves a Ge-induced transient homoepitaxial growth step followed by 3C nucleation when large terraces are formed by step faceting. Lateral expansion of the 3C islands leads to orientation selection and twin boundary elimination. Similar results can be obtained when applying a Si-based pre-deposition treatment so that the crucial transient homoepitaxial step is promoted in fact by the presence of a liquid phase itself, no by its chemical nature.

Vapor–liquid–solid (V–L–S) growth of SiC on (100) diamond substrate is reported. The crystalline quality is evaluated by transmission electron microscopy (TEM). Diffraction contrast (CTEM) observations allowed confirming the growth of fully lattice relaxed SiC 3C-type crystalline structure. Defects as dislocations at the diamond/SiC interface and stacking faults, in the thick SiC layer are revealed by high resolution TEM and CTEM. From the invisibility criteria, using dark field observations, 〈110〉 type Burger vector are identified.

International audience; The present study reports the fabrication of localized p-doped silicon carbide zones on 4H-SiC substrate. Selective epitaxial growth of p-doped SiC was performed using the vapour–liquid–solid transport in Al–Si liquid phase. Focus was made on the understanding of the mechanism involved during such growth. It was shown that despite the need of starting the growth during the heating ramp, the deposition proceeds in a 2D manner at low temperature. Rather high growth rates were obtained (56.7–380 nm/min) which are related to the thinness of the liquid phase (< 3 μm). Argon carrier gas leads to an increase of growth rate compared to H2 due to the reducing effect of this latter gas. The results revealed that the surface morphology was more affected by the initial Si content of the liquid than by the growth rate. It is proposed that the Si content of the liquid is a very influent parameter because of its importance in the competition between SiC or Al4C3 stabilization.

The effect of germanium (Ge) on n-type 4H-SiC is experimentally studied by electrical characterization of homoepitaxial layers grown by chemical vapor deposition (CVD). Measurements show that electrical properties of epitaxial layers can be changed by intentional incorporation of germane (GeH4) gas during the deposition process. On the nanoscale, two-dimensional mappings acquired with conductive atomic force microscopy show preferential conductive paths on the surface of Gedoped samples, which are related to the presence of this isoelectronic impurity. Hall effect measurements confirm that also macroscopic electrical properties of n-type 4H-SiC are improved due to incorporation of Ge into SiC during CVD growth. In particular, despite equal free electron concentration, enhanced mobility in a wide temperature range is measured in Ge-doped samples as compared to a pure 4H-SiC layer. Based on our results from Hall effect measurements as well as admittance spectroscopy and deep level transient spectroscopy, it is speculated that Ge influences the generation and annealing of other point defects and thus helps to reduce the total concentration of defects.

The aim of this study was to find conditions allowing the "natural" formation of a regular and controllable step bunched morphology on a 4H-SiC seed without the need of any SiC deposition. This was performed by melting a bulk piece of Si on a 4°off 4H seed in the temperature range of 1500 - 1600°C, for 15 min. After etching the remaining Si, the 4H surface was found to be successfully highly step bunched with steps very parallel and regular. A mechanism of dissolution-precipitation was proposed, which could occur both on a short (step to step) and long (centre to periphery) range. This process is kinetically limited at low temperature (1500-1550°C) and considered to be close to the equilibrium at 1600°C., Materials Science Forum, 858, ISSN:0255-5476, ISSN:1662-9752, Silicon Carbide and Related Materials 2015, ISBN:978-3-0357-1042-7, ISBN:3-0357-1042-2

The growth kinetics of 3C-SiC heteroepitaxial layers on α-SiC substrates by a vapor–liquid–solid (VLS) mechanism in Ge-Si melts was investigated. Various parameters were studied such as temperature, melt composition, crucible inner diameter, propane flux, and substrate nature (polytype, polarity, and misorientation). It was found that the growth rate increases with increasing temperature, propane flux, Si content of the melt, and misorientation of the substrate. The calculated activation energy (from 4.7 to 6.6 kcal/mol depending on the substrate type) is very small suggesting that the limiting process is the diffusion of the dissolved carbon inside the melt. The carbon solubility inside the melt mainly affects the carbon dissolution kinetics from the gas phase. The results also suggest that surface effects are important through the layer polarity, the roughness and the emerging defect density.

We report the results of a series of LTPL (Low Temperature PhotoLuminescence) investigation performed on n-type, non-intentionally doped, 4H-SiC samples. We focus on the defect structure introduced by a growth fault in the stacking sequence. We treat the fault as a 3C quantum well embedded in a 4H-SiC matrix and use a simple 2-dimensional approximation to deduce the extent of the lattice perturbation associated with a given defect. We show that the intrinsic type-II nature of the band alignment, combined with the effect of the spontaneous polarization, must result in a double bound-exciton signature per well, which is resolved for the first time. The comparison with experimental results confirms also that, after a relatively small critical layer thickness, the back conversion from cubic to hexagonal remains an unsolved problem.

We report on the growth of thin, aluminium doped, homo-epitaxial layers of 4H-SiC using a threefold mixture of purified hexamethyldisilane (HMDS) admixted with propane (P) and trimethylaluminium (TMA). The growth has been performed in an AP-CVD, cold wall, vertical reactor in which the growth of 4H-SiC layers using HMDS admixed with propane has been well demonstrated. To control, as a function of the growth parameters, the amount of aluminium incorporated in the epitaxial layers SIMS, C(V) and Raman experiments were done. They show that good quality p-type epitaxial layers can be grown, up to a final aluminium concentration of about 2 x 10 19 at cm -3 . Comparing with the more standard gas system silane/TMA/P, we have found that there is no significant difference. The total amount of Al incorporated is about the same and, in both cases, the incorporation starts to be limited when the growth temperature reaches 1500 °C. In both cases, also, the C/Si ratio and the growth rate influence the aluminium concentration.

In order to process n-type channel MOSFETs on (1120)-oriented 4H-SiC wafers one has to optimise, independently, many different steps. First is the growth of the active epitaxial layer, including the effect of p-type doping. Next is the oxidation and, finally, the n-type implantation for source and drain formation. In this work, we investigate the growth and doping of the p-type doped epitaxial layer on the (1120)-oriented substrate using, both, SIMS, low temperature photoluminescence measurements and Hall effect measurement to control the final doping level. Next we investigate the change in oxidation kinetics with respect to the conventional (0001) surfaces. Finally, we evaluate the efficiency of implantation and annealing processes.

International audience; The stacking order of multilayer graphene has a profound influence on its electronic properties. In particular, it has been predicted that a rhombohedral stacking sequence displays a very flat conducting surface state: the longer the sequence, the flatter the band. In such a flat band, the role of electron electron correlation is enhanced, possibly resulting in high T-c superconductivity, magnetic order, or charge density wave order. Here we demonstrate that rhombohedral multilayers are easily obtained by epitaxial growth on 3C-S1C(111) on a 2 degrees off-axis 6H-SiC(0001). The resulting samples contain rhombohedral sequences of five layers on 70% of the surface. We confirm the presence of the flat band at the Fermi level by scanning tunneling spectroscopy and angle-resolved photoemission spectroscopy, in close agreement with the predictions of density functional theory calculations.

We report on the optical study of double heterostructures InP/InAlAs/InP grown on (100) substrates at various V/III molar ratios, grown by metal-organic chemical vapor phase epitaxy (MOCVD). Photoluminescence experiments have been performed to investigate the optical transitions in these samples. In order to identify the optical transition at inverted interface (InP grown on InAlAs) at 1.25 eV, previously assigned to a type II interface band structure, a study based on transfer matrix technique under the envelope function approximation has been performed. Taking into account the formation of InAsxP1−x thin graded layer located at the inverted interface (between InP and InAlAs), a simulation indicates that this recombination originates in fact from a type II interface band structure between electrons confined on InAsP and holes located on top of the InAlAs valence band. Detailed studies of photoluminescence spectroscopy (PL) properties of InAlAs epilayer at low temperature indicate that the PL spectrum, recorded at low temperature (12 K) on (100) substrate sample with V/III=50, shows double effects: the presence of a clustering and of a natural superlattice (SL) due to composition modulation. For other samples with different V/III, the composition modulation disappears so that only a clustering effect remains.

In this paper, we will describe a detailed experimental study on the behavior of Ge incorporation into 4H-SiC during its homoepitaxial growth by CVD. Addition of GeH4 precursor to the standard chemical system SiH4 + C3H8 was investigated as a function of various growth parameters. Its effect on surface morphology, layer quality and purity was followed. All these results will allow proposing an exhaustive picture of Ge incorporation mechanism into 4H-SiC with the possible benefits of such impurity incorporation in the silicon carbide lattice.

By comparing the PL spectra taken for two double heterostructures InP–InAlAs–InP grown by MOCVD on (311) B and (100) substrates we have shown that the heterostructures grown on (311) B have better optical quality than the one grown on (100). The main reason for this is the fluctuation of composition within the second sample. Thus, we have focused our studies in this work, by photoluminescence (PL) and linear polarized photoluminescence spectroscopy (PPL), on the staggered band lineup inverse interface of the InP/InAlAs/InP double heterostructure grown on (311) B . At low temperature, this interface induces a photoluminescence transition at 1.25 eV, thus giving a new possibility to achieve an optical emission with a photon energy smaller than the band gap energy of both semiconductors forming the heterostructure. It can be shown that this luminescence line shifts logarithmically towards higher energy when the injection is increased. PPL experiments reveal a variation of a degree of polarization for normal and inverted interface transition. This suggests that the two interfaces are not equivalent. On the other hand, for heterostructure grown on (100) substrate and for high laser injection we observe a new luminescence band on the high energy side of the luminescence in InAlAs bulk material. This new emission is attributed to a luminescence of a disordered superlattice due to composition modulation related to the value of the V/III molar ratio.

International audience; This works deals with the localized growth of SiC on monocrystalline (100) diamond surface. It describes an attempt of selective epitaxy using vapor–liquid–solid (VLS) transport. Patterns of Al–Si stacking were melted and fed by propane. Morphology, structure and doping type of the SiC deposit were evaluated. The deposit was found to be successfully selective but polycrystalline, with the 3C-SiC polytype. Study of the initial step of growth showed that SiC nucleation occurs without any propane addition but just through the interaction of liquid Al–Si and diamond via a dissolution/precipitation process. The VLS transport mainly assists the growth of these nuclei by providing a secondary carbon source. This explains the random nucleation and the polycrystalline growth. Despite this, the deposit was dense enough to perform some preliminary electrical measurements which show encouraging results.

A photoluminescence (PL) study of direct interface (InAlAs/InP) properties in InP/InAlAs heterostructures grown by metal–organic chemical vapor deposition on (1 0 0) InP substrate has been carried out. At low temperature, a broad PL band ( FWHM =120 meV ) has been observed around 1 eV which is attributed to direct interface recombination. This PL line was strongly blue shifted ( 100 meV over three decades) when increasing the excitation density, and no saturation of the associated PL intensity was observed. This is the characteristic of type II or mixed type I–II transition.

Since a few years, VLS transport is studied not only for homoepitaxial SiC growth but also for SiC selective epitaxial growth (SEG). In this approach, a stacking of silicon and aluminum layers is deposited on the substrate and patterns are created by photolithography. Upon melting, the Al-Si liquid droplets are fed by propane to obtain the SEG of p-doped SiC. In this work, the growth mechanisms were deeper investigated, in particular the influence of the carrier gas (H2 or Ar) and the growth temperature. SEG experiments showed higher growth rates than those measured in the standard configuration (nonselective growth). Moreover, the SiC layers exhibited step-bunched areas characteristic of liquid phase growth but also areas with morphological features due to a disruption of the step-bunching growth mode.

International audience; The objective of this study is to grow Si-SiC core-shell nanowires (NWs) for bio-nano-sensors. The idea is to benefit from the electronic transport into the Si core NW and from the biocompatibility of the SiC shell all around the Si NW. Silicon nanowires (NWs) have been first obtained by a top-down approach. Before carburization, in situ deoxidation under H-2 allowed significant smoothening and faceting of the Si NWs sidewalls. Then, Si NWs have been carburized under methane or propane at atmospheric pressure and at temperatures >= 1000 degrees C. Carburization of Si NWs leads to Si-SiC core-shell NWs with a thin (similar to 3 nm), continuous and single crystalline cubic SiC shell. The 3C-SiC shell has been further thickened by chemical vapor deposition and preferential growth of 3C-SiC has been observed on the sidewalls of NWs. Based both on the electronic transport properties of silicon and on the biocompatibility of SiC, these new 1D-nanostructures could be an ideal object for nano-bio-sensors.

International audience; This work reports on the stabilization of 3C–SiC polytype during heteroepitaxial growth by vapor–liquid–solid (VLS) on on-axis and 2° off-axis 6H–SiC(0001) substrates using Si–Ge as liquid phase. It was found that, depending on growth conditions (mainly temperature or nitrogen amount in the reactor), the deposit could be either a complete 3C or 6H–SiC layer or even a mixture of both polytypes. The proportion of 3C inside the deposit increases when 1) nitrogen amount in the reactor increases or 2) temperature is decreased. Though the effect of temperature could be explained in terms of 3C–SiC initial island dissolution, the influence of nitrogen is less obvious but it is shown to be effective at the early stage of growth. Several hypotheses are proposed such as SiC lattice modification by N incorporation or surface effects during the early stage of growth.

International audience; In this work, we present and compare the results obtained from different Si-based melts (Ge–Si, Al–Si and Al–Ge–Si) for growing SiC layers on α-SiC substrate by vapour–liquid–solid (VLS) mechanism. It was found that, depending on melt composition, the deposit could be either a complete 3C or α-SiC layer or even a mixture of these polytypes. The binary Al–Si melt leads systematically to a highly p-type homoepitaxial α-SiC deposit while Ge–Si melt gives a non-intentional n-type doped layers of either 3C or 6H polytypes depending on growth conditions. However, highly p-type doped 3C heteroepitaxial deposit can be obtained if a small amount of Al is added to the Ge–Si binary liquid phase. This means that the VLS mechanism is very flexible and allows growing either n- or p-type SiC layers of 3C or 6H polytypes.

Discrete series of lines have been observed for many years in N‐Al DAP (Donor Acceptor Pair) spectra in 3C‐SiC. Unfortunately, up to now, there has been no quantitative analysis for the splitting of lines in a given shell. This is done in this work for N‐Al DAP spectra in 3C‐SiC. The samples were non‐intentionally doped 3C‐SiC layers grown by CVD on a VLS seeding layer grown on a 6H‐SiC substrate. From low temperature photoluminescence measurements, strong N‐Al DAP emission bands were observed and, on the high energy side of the zero‐phonon line, we could resolve a series of discrete lines coming from close pairs. Comparing with literature data, we show that the splitting energy for a given shell is constant and, to explain this shell substructure, we consider the non equivalent sets of sites for a given shell. Results are discussed in terms of the ion‐ion interaction containing third and forth multipole terms.

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 (mu-R) and, finally, low temperature photoluminescence (LTPL) spectroscopy. From SIMS measurements we find Ga concentrations in the range of 10(18) cm(-3), systematically accompanied by high nitrogen content. In good agreement with these findings, the mu-R spectra show that the Ga-doped samples are n-type, with electron concentrations close to 2x10(18) 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, a small feature resolved at 2.35 eV comings from neutral Ga bound excitons. Quantitative analyses of the DAP transition energies in the Ga-doped and witness sample gave 346 meV for the optical binding energy of Ga acceptors in 3C-SiC against 251 meV for the Al one. The conditions for the relative observation of Ga and Al related LTPL features are discussed and the demonstration of room temperature luminescence using Ga doping is done. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3455999]