Papers by Author: Yves Monteil

Abstract: We report the results of a SIMS and micro-Raman investigation performed on cubic (3C) SiC crystals grown on hexagonal SiC seeds using a Ge-Si bath and the so-called Vapor Liquid Solid growth technique. From SIMS measurements, we find a Ge concentration which, roughly, scales like the Ge concentration in the melt and, in term of micro-Raman measurements, explains the presence of weak but discernable Ge-Ge peaks around 300 cm-1. Since no similar Si-Si vibrations are found, this discard the possibility of having at the same time both Ge and Si constitutional super-cooling with two separate Ge and Si phases.

Abstract: We report an optical investigation of cubic Silicon Carbide (3C-SiC) layers grown on 6H-SiC substrates by Chemical Vapour Deposition and Vapour-Liquid-Solid mechanism. Micro- Infrared reflectance ('-IR), micro-Raman ('-Raman) and low temperature photoluminescence spectroscopies were used for the characterisation of such layers. '-IR measurements showed unusual optical behaviour of 3C-SiC layers. The difference of refraction index between the 3C-SiC film and the 6H-SiC substrate cannot explain this result. The experimental '-IR reflectance spectrum was modelled by introducing a thin (thickness ≤ 0.5 'm) metallic-like (doping ≥ 1020 at.cm-3) interfacial film between the layer and the substrate. The photoluminescence spectra revealed the presence of a peak which may be attributed to recombination at the 3C/6H interface. All these results suggest the presence of a two dimensional electron gas at the interface.

Abstract: We applied picosecond dynamic grating technique for studies of carrier dynamics in ntype DPB(double positioning boundary)-free 3C-SiC (111) epilayer grown by VLS (vapour-liquidsolid) mechanism on 6H-SiC (0001). The measurements of bipolar diffusion coefficient D and carrier lifetime τR in the samples at various pump energies (0.5 – 3.0 mJ/cm2) and temperatures (9 – 300 K) provided the values of bipolar mobility of ~ 80 cm2/Vs and τR = 1.5 - 2.0 ns at 300 K. The ionized impurity scattering, dominant at T < 100 K, and carrier-density dependent lifetimes in 10- 300 K range were attributed to contribution of trapping centers which electrical activity saturates at high carrier density.

Abstract: We report on the heteroepitaxial growth of 3C-SiC layers by Vapor-Liquid-Solid (VLS) mechanism on various α-SiC substrates, namely on- and off-axis for both 4H and 6H-SiC(0001), Si and C faces. The Si-Ge melts, which Si content was varied from 25 to 50 at%, were fed by 3 sccm of propane. The growth temperature was varied from 1200 to 1600°C. It was found that singledomain 3C-SiC layers can be obtained on 6H-SiC off and on-axis and 4H-SiC on-axis, while the other types of substrate gave twinned 3C-SiC material. As a general rule, one has to increase temperature when decreasing the Si content of the melt in order to avoid DPB formation. It was also found that twinned 3C-SiC layers form at low temperature while homoepitaxy is achieved at high temperature.

Abstract: Vapor-Liquid-Solid was used for growing boron doped homoepitaxial SiC layers on 4HSiC( 0001) 8°off substrates. Si-based melts were fed by propane (5 sccm) in the temperature range 1450-1500°C. Two main approaches were studied to incorporate boron during growth : 1) adding elemental B in the initial melt, with two different compositions : Si90B10 and Si27Ge68B5; the growth was performed at 1500°C; 2) adding B2H6 (1 to 5 sccm) to the gas phase during growth with a melt composition of Si25Ge75; the growth was performed at 1450°C. In most cases, the growth time was limited by liquid loss due to wetting on the crucible walls. The longer growth duration (1h) was obtained when adding B2H6 to the gas phase. In the case of Si90B10 melt, the surface morphology exhibits large and parallel terraces whereas the step front is more undulated when adding Ge. Raman and photoluminescence characterizations performed on these layers confirmed the 4H polytype of the layers in addition to the presence of B which results in a strong B-N donor-acceptor band. Particle induced γ-ray emission was also used to detect B incorporation inside the grown layers.

Abstract: Growing good quality SiC epitaxial layers at temperature lower than 1400°C is a challenging problem which could help reducing the costs, increasing the safety of the process or even give new perspectives. Toward this aim, liquid based growth techniques have been used. The Si-based melts should be carefully chosen considering several criteria. Furthermore, the implementation of a liquid phase for growing SiC epilayer can be performed in various manners (dipping or VLS mechanism) so that one has to choose the more appropriate technique. The discussion is illustrated with several results showing that the growth of SiC from a liquid phase at low temperature can address various important technological points such as experimental safety, ptype doping, on-axis or selective epitaxy. The recent demonstration of single-domain 3C-SiC heteroepitaxial layers on hexagonal SiC substrates confirms that liquid based growth has still unexpected qualities.

Abstract: The epitaxial relationship of Si deposited on 3C-SiC was studied using both free standing 3C-SiC(100) material from Hoya and 3C-SiC thin layers deposited on Si(100) as substrates. The conditions of Si growth were varied depending on the substrate. When Si is deposited at 1000°C on (001) 3C-SiC, it is in perfect epitaxial relation with the SiC layer [100]Si//[100]SiC and [001]Si//[001]SiC. After a 20 ms flash lamp pulse on the same sample, which has the effect of fast melting of the Si top layer only, the defects in the Si are eliminated. Using free standing 3C-SiC, the deposition temperature was not limited by the Si melting point so that it was fixed at 1500°C in order to form a set of Si liquid droplets on the surface with diameters ranging from 5 to 20 μm. Surprisingly more than 60% of the Si droplets exhibit the epitaxial relation [110]Si//[001]SiC and [111]Si//[110]SiC after crystallization. The occurrence of this epitaxial relationship can be understood in terms of lattice mismatch reduction from 20% to 18.3%. The conditions of crystallization, most probably the cooling rate, seem to have a strong effect on Si orientation.

Abstract: Using the Vapor-Liquid-Solid mechanism in Ge-Si melts we have grown 3C-SiC layers on top of <0001>-oriented, Si face, 6H-SiC substrates. The surface morphology was free of spiral growth but highly step bunched. The 3C-SiC polytype was identified by micro- Raman spectroscopy and confirmed by low temperature photoluminescence. Electron backscattering diffraction mapping showed that the upper side of the layers is single-domain, i.e. that the 3C-SiC material displays only one in-plane orientation. Cross-sectional and planeview TEM investigations allowed detection of double positioning boundaries but only confined at the substrate/epilayer interface. The main additional defects found were stacking faults (SF) with a density of ~ 4.103 cm-1. Forming at the interface, they propagate through the epitaxial layer.

Abstract: Al-Si and Ge-Si systems were studied for selective epitaxial growth (SEG) of 4H-SiC by the Vapour-Liquid-Solid mechanism. Al-Si and Ge-Si bilayers stackings were deposited on 8° off, Si face, 4H-SiC substrates. After patterning of the layers, the samples were heated up to 1000°C and 1220°C, respectively, for Al-Si and Ge-Si stackings in order to melt the layers. Propane was introduced either during the initial heating ramp, before melting of the alloy, or after reaching the temperature plateau. It was found that introduction of propane before melting was a key parameter in order to improve the homogeneity of the deposit. In both cases, SEG of SiC was achieved. However, the best results were obtained with Ge-Si system giving smooth and uniform ∼100 nm thick epitaxial deposits on all the pattern sizes and shapes. Ge incorporation in the SiC was found to be rather limited but homogeneous in the layer.

Abstract: The vapour-Liquid-Solid mechanism was used for growing epitaxial SiC layers on onaxis 6H-SiC and 4H-SiC substrates. By feeding Al70Si30 melts with propane, homoepitaxial growth was demonstrated down to 1100°C on both polytypes. At this temperature, the surface morphology is rough and non uniform with spiral growth forming large hillocks at the places where screw dislocations emerge from the substrate. Raman spectroscopy confirms the absence of the 3C-SiC polytype and shows the high Al doping of the layers. This growth temperature of 1100°C is the lowest one ever reported for growing homoepitaxial layers on low tilt angle SiC substrates. Increasing the temperature to 1200°C eliminates these hillocks but creates other morphological features due to fast substrate etching at this high temperature before growth starts.