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Structural and optical studies of B x Ga 1− x As epilayers, grown by metal organic chemical vapor deposition (MOCVD), at different growth temperatures (580 °C and 500 °C), have been achieved by high-resolution X-ray diffraction (HRXRD) and photoluminescence spectroscopy (PL). They have shown that the boron content increases up to 8% with decreasing growth temperature. Low temperature (10 K) PL study has shown an asymmetric broad PL band around 1.34 eV, and a decrease of the intensity with increasing boron composition. The evolution of the emission energy versus temperature can be described by the Varshni law for the high temperature range, while a relative discrepancy has been found to occur at low temperature. Moreover, depending on the temperature range, the PL intensity quenching is found to be thermally ensured by three activation energies for the smallest boron composition ( x b ≈ 3%) and by two for the highest ( x b ≈ 8%) one. These results are attributed to the localized states induced by the non-uniform insertion and the clustering of the boron atom in BGaAs bulk.

Structural and optical studies of In y Ga 1− y As/GaAs and B x In y Ga 1− x − y As/GaAs quantum wells, grown by Metal Organic Chemical Vapor Deposition (MOCVD), with the same indium composition, have been achieved by High-resolution X-ray Diffraction (HRXRD) and Photoluminescence spectroscopy (PL). An important fraction of indium (36%) has been incorporated into GaAs and BGaAs confirmed the growth conditions. The strain effects have been reduced by In incorporation into BGaAs which show that a B x In y Ga 1− x − y As can be grown lattice-matched to GaAs. It has been shown that the BInGaAs PL band shifts significantly to low energy side (of a bout 50 meV) compared to InGaAs. The temperature dependence of the BInGaAs PL peak energy has shown an abnormal behavior. Based on these experimental results, we have suggested that the carrier recombination mechanisms in the BInGaAs QWs result from exciton-localization like mode. These results are attributed to the localized states induced by the clustering and the non-uniform insertion of boron atoms in BInGaAs QW.

The density functional theory calculations of structural phase transition, elastic constants and electronic structure of the CuAlX 2 (X = S, Se, Te) have been reported using the full potential linear muffin-tin orbital (FP-LMTO). In this approach, the local density approximation is used for the exchange-correlation potential. Results are given for lattice constant, bulk modulus, and its pressure derivative, band structure, density of states and pressure dependence of energy gaps. We note that these compounds are semiconductors with direct energy gaps. The valence-band maximum and conduction-band minimum are located at Γ . Our results are compared with previous theoretical calculations and experimental data. The elastic constants at equilibrium in BCT structure are also determined.

In this study, the EELS results revealed the great sensitivity of InP compound submitted to Ar + or N + ions at low energy. The preliminary treatment of InP by the Ar + ions was useful as part of the cleaning process of the surface. Further argon ions bombardment on cleaned InP led however to breaking of chemical bonds In–P, with desorption of phosphorus atoms and appearance of In metal distributed on InP. The damaged InP by Ar + ions, constituted the diphase (In; InP) system of depth of about 30 A, involving a superficial roughness. The In metal proportion on such a system was determined by a calculation method based on the experimental EELS spectra of pure In and InP. We submitted the heated and no heated system (In; InP) to nitrogen ions bombardment. The nitrogen reacted with the In metal to compensate the phosphorus vacancies so that InN species were formed. The heating of (In; InP) system at 450 °C, allowed the surface reconstruction with elimination of defects due to the structure and the roughness. The temperature also caused the coalescence of In metal towards the surface. Because of the physical stability of the interface of heated (In; InP) system, the nitrogen reacted with the outmost layers of In metal to form a homogeneous layer of InN of thickness estimated at 20 A. We associated to the EELS the TRIM (Transport and Range of Ions in Matter) simulation method in order to show the mechanism of interaction Ar + or N + ions-InP and determine the disturbed depth as a function of the energy. The EELS alone was not able to give us with accuracy the disturbed depth of the target by these ions.

BGaAs epitaxial layers were grown by metalorganic vapour phase epitaxy (MOVPE) on (100) GaAs vicinal substrates using diborane, triethylgallium and arsine as precursors. For growth temperatures of 580 and 610 °C, we studied the boron incorporation in the epilayers, their boron surface composition and their growth mode as a function of the diborane flow-rate, using respectively X-ray diffraction, X-ray photoelectron spectroscopy and Atomic Force Microscopy. We observed that increasing the diborane flow-rate strongly favours the development of step-bunching. This trend was related to a pronounced boron enrichment of the surface, as a consequence of a surface segregation of boron. These results suggest that boron behaves as a surfactant during the MOVPE growth of BGaAs and particularly increases the surface diffusion length of gallium adatoms. For excessive diborane flow-rates, a dramatic roughening of the epilayer surface is first observed and then, phase separation occurs.

The goal of this research is to highlight the effectiveness of associating the spectroscopic methods EELS and EPES in the study of thin film grown on substrates. We use the great sensitivity of the Electron Energy Loss Spectroscopy (EELS) and the Elastic Peak Electron Spectroscopy (EPES) to study native InPO4 oxide of thin thickness (10 A) grown on InP by UV/ozone oxidation. By varying the primary energy of the electron beam and the incidence angle, we give interesting results related to the chemical and the physical analyses of InPO4/InP system. These spectroscopic methods reveal the homogeneity of the chemical composition of InPO4 on the surface. Furthermore, the electron irradiation of InPO4/InP leads to the breaking of chemical bonds between the species of InPO4 and InP to form a new oxide In2O3 on the surface. We show that the heating of InPO4/InP at 450 °C in UHV allows a good reconstruction of the surface with elimination of defects on the surface and at the interface. Thus, the surface becomes more stable to impede all oxidation processes due to the electron beam irradiation even for a time as long as 30 min.

The interaction of ions with matter plays an important role in the treatment of material surfaces. In this paper we study the effect of argon ion bombardment on the InSb surface in comparison with the InP one. The Ar+ ions, accelerated at low energy (300 eV) lead to compositional and structural changes in InP and InSb compounds. The InP surface is more sensitive to Ar+ ions than that of InSb. These results are directly inferred from the qualitative Auger electron spectra (AES) and electron energy loss spectroscopy (EELS) analysis. However, these techniques alone do not allow us to determine with accuracy the disturbed depth in Ar+ ions of InP and InSb compounds. For this reason, we combine AES and EELS with the simulation method TRIM (transport and range of ions in matter) to show the mechanism of interaction between the ions and the InP or InSb and hence determine the disturbed depth as a function of Ar+ energy.

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.

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.

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.

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.

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.

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.

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.

The temperature- and frequency-dependent electrical properties of SiO2/3C–SiC/6H–SiC structures have been studied. Capacitance measurements indicate that the single-domain 3C–SiC film is doped with an average concentration of 8.4×1016 cm-3. One nitrogen donor level and a shallow donor level were found. The measured interface state density near the conduction band edge of 3C–SiC is below 1011 cm-2 eV-1 and increases towards mid-gap as obtained from conductance and capacitance measurements. Our results are consistent with the assumption that the interfaces of SiO2/n-type SiC consist of two different kinds of interface traps.

Due to the large differences in lattice parameters and thermal expansion coefficients, the heteroepitaxial growth of 3C-SiC on Si mainly results in highly defective layers on strongly bent wafers. The defects may not be detrimental for very basic applications, but the bow is. In this article, we review several attempts to reduce the final curvature after epitaxial growth of 3C-SiC. One is the use of the "checkerboard" carbonization process which creates a macroscopic balance of the stress by the formation of a regular network of compressed and tensed areas. Another approach proposes to create, in situ, a random patchwork of tensed and compressed areas during the carbonization step. The other attempts use substrates other than standard Si, namely silicon on insulator and Si-Ge substrates for compliance effect and closer thermal expansion mismatch with SiC, respectively. All techniques provoke a significant reduction of the strain in the deposited 3C-SiC layers.

Vapor–liquid–solid mechanism was used for growing epitaxial SiC layers on on-axis 6H–SiC and 4H–SiC substrates. By feeding Al70Si30 melts with propane, homoepitaxial growth was demonstrated on both polytypes down to 1100 °C, which is the lowest temperature ever reported for growing homoepitaxial layers on low tilt angle SiC substrates. However, at this temperature, the surface morphology is rough and non-uniform with spiral growth, forming large hillocks at the places where screw dislocation emerges from the substrate. Raman spectroscopy confirms the absence of 3C–SiC polytype and shows the high Al doping of the layers. Increasing temperature to 1200 °C eliminates these hillocks but creates other morphological features due to fast substrate etching at this high temperature before growth starts. These defects were reduced in size by introducing propane at 1100 °C before ramping to 1200 °C and completely eliminated by increasing the Si content of the melt to 50 at%.

Epitaxial 3C-SiC(1 1 1) films were grown on 6H-SiC(0 0 0 1) Si face on axis substrates by chemical vapor deposition under H 2 , SiH 4 and C 3 H 8 in a cold wall vertical reactor. Two temperatures were studied (1450 and 1700 °C) with various C/Si ratio and deposition time. It was found that under conditions giving high lateral growth (low C/Si and/or high temperature), homoepitaxial growth occurred even at temperatures as low as 1450 °C. For other conditions, the 3C-SiC polytype was detected and always together with the formation of double positioning boundaries whose density was found to depend on the growth conditions but not on the initial surface reconstruction. Single domain enlargement was observed when growth was performed at 1700 °C over a nucleation layer grown at 1450 °C.

Owing to the lack of available thermodynamic data based on experimental measurements of heat capacity, decomposition reaction or vapour pressure measurements, the problem of BAs stability is considered. We propose a new set of thermodynamic data for enthalpy of formation, entropy and Gibbs free energy of Bas compound. By using thermodynamic database, our approach is based on the semi-empirical trends and analogy in the variation of those quantities for several binary series in different III–V systems like arsenides, nitrides and phosphides. Thus, the values for BAs were derived by extrapolation from Al to boron-based compounds (BAs, BP and, BN). For pure BAs(s), we predict a low enthalpy of formation in the standard state of Δ f H 0 ( BAs ) ≈ - 30 kJ / mol at 300 K and a Gibbs free energy of Δ f G 0 ( BAs ) ≈ - 40 ± 5 kJ / mol indicating a lower stability of this compound than GaAs. Those values are contradictory discussed with trends in the cohesive energy of several III–V systems. A cohesive energy of ∼900 kJ/mol (9.4 eV) is proposed in agreement with Philips's rule.

Optical studies of B x Ga 1− x As/GaAs epilayers grown by Metal Organic Chemical Vapor Deposition (MOCVD), with boron composition ≤ 7%, have been achieved by photoluminescence spectroscopy (PL) as a function of the excitation density and the sample temperature (10–300 K). The Raman scattering have shown a linear variation between boron composition and Raman shift of the optical phonons modes. It has shown that the BGaAs PL band shifts to low energy side when the boron composition is ≤ 2.5% compared to the GaAs one. But this band increases slowly as the boron content increases in range 2.5% to 7%. Blue shifts of the PL bands were observed when increasing the excitation density. The temperature dependence of the PL peak energy has shown an S-shaped behavior. Based on these experimental results, we have suggested that the carrier recombination mechanisms in the BGaAs epilayer result from exciton-localization like mode. These experimental results show that boron incorporation does not cause a great modification of the band structure in B x Ga 1− x As alloys compared to the pure GaAs.

An approach for the defect density reduction in 3C-SiC epitaxially grown on Si is to improve the quality of the carbonized layer during the early stage of growth. For this reason the conventional carbonization process was replaced by a slower and nearer equilibrium carbonization method. Carbon is introduced by implantation into oxide of an oxidized Si substrate, near the SiO2/Si interface, and then it is transferred to the Si surface by annealing. Good quality 3C-SiC grains are formed embedded into the Si substrate, which are absolutely flat at the SiO2/Si interface. Another advantage of the new carbonization process is the elimination of the cavities due to the suppression of Si out-diffusion.

The so-called VLS (Vapour-Liquid-Solid) mechanism in an Al-Si melt has recently demonstrated the capability to grow at low temperature single crystalline 4H-SiC layers, with a high Al content. Using the newly developed VLS technique, we have deposited several 4H-SiC layers and determined the incorporated Al level by SIMS (Secondary Ion Mass Spectroscopy). Depending on the sample, we have found that the SIMS doping level ranges from 5x1019 to 1x1021 at.cm-3. This last value is the highest one reported so far for in-situ doped SiC:Al. From TEM (Transmission Electron Microscopy) analyses we show that the layers are single crystals, with a high density of defects located only at the lower interface and no foreign phase inclusion. These results compare well with the ones obtained in previous works using alternative doping techniques, like ion implantation, chemical vapour deposition or sublimation. It thus suggests that Al solubility limit in SiC is rather temperature independent.

One of the problems with Si(001)/3C-SiC templates is that they involve highly defective interfaces due to the presence of misfit dislocations, voids and planar defects that degrade the SiC layer quality. A way to accommodate the high lattice mismatch between these materials and reduce the voids density is to carbonize the Si substrate before the epitaxial growth. In this contribution an alternative way to reduce planar defects density is presented by analyzing the relationship between planar defects and voids. Planar view and cross section transmission electron microscopy micrographs show a diminution of planar defects in the regions surrounding the voids. Due to the lower elastic energy over the voids and/or to a lateral growth in these regions, the generation of planar defects is partially deactivated, improving locally the crystalline quality of the SiC layer. The introduction of such cavities can be thus seen as a new parameter of Si/SiC templates design.

We report on the study of the p-type doping of 4H-SiC material using HexaMethylDiSilane/TriMethylAluminium/Propane (HMDS/TMA/P) system in place of the usual Silane/TriMethylAluminium/Propane (S/TMA/P) precursors. The influence of growth parameters such as TMA flow, growth rate or C/Si ratio is investigated. The aluminium incorporation level is deduced from both by C(V) (mercury probe) and SIMS measurements. The presence of aluminium in the layers is confirmed by non-destructive optical micro-Raman experiments. Good quality p-type, aluminium doped 4H-SiC layers can be grown using HMDS/TMA/P system. The amount of aluminium in the layers can be controlled by choosing the growth conditions and an aluminium concentration as high as 2x1019 at.cm-3 has been reached.Finally, comparing the two HMDS/TMA/P and S/TMA/P systems, no difference in aluminium incorporation has been found.

Al-Si patterns were formed on n-type 4H-SiC substrate by a photolithographic process including wet Al etching and Si/SiC reactive ion etching (RIE) process. RF 1000°C annealing under C3H8 flow was performed to obtain p+ SiC layers by a Vapour-Liquid-Solid (VLS) process. This method enables to grow layers with different width (up to 800 µm) and various shapes. Nevertheless the remaining Al-based droplets on the largest patterns are indicators of crack defects, going through the p+ layer down to the substrate. SIMS analyses have shown an Al profile with high doping concentration near the surface, high N compensation and Si/C stoechiometry variation between the substrate and the VLS layer. The hydrogen profile follows the Al profile in the VLS layer with an overshoot at the VLS/substrate interface. I-V measurements performed directly on the semiconductor layers have confirmed the formed p-n junction and allowed to measure a sheet resistance of 5.5 kW/ı

We report an experimental investigation of the residual (n-type) and intentional (p-type) doping level of epitaxial layers grown on a-cut 4H-SiC substrates. Using SIMS, C(V) measurements, low temperature photoluminescence and Hall effect investigations, we show that nitrogen incorporates 3 times more than usually found for surfaces. Conversely, aluminum incorporates 8 times less. Altogether, this is in excellent agreement with previous results from stepcontrolled epitaxy.

The evolution of defects versus thickness has been investigated in three different freestanding 3C-SiC samples, using TEM (Transmission Electron Microscopy) and LTPL (Low Temperature Photo-Luminescence) spectroscopy. In all samples, the stacking fault density reduces rapidly within the first 20 µm of the growth. Then it remains constant, at about 5x103 cm-1 up to the end. This behavior is attributed to the easy generation of stacking faults, even under a very low thermal stress, as in-situ experiments reveal. On the opposite the elimination of inversion domains, by bending boundaries during the growth, is found to be sample dependant. This is in good agreement with LTPL results.

In the so called FLASiC process, due to the transparency of the 3C-SiC, the irradiated energy is selectively absorbed at the SiC/Si interface where the most defected part of the 3C-SiC film exists. The Si at the interface melts up to a depth depending on the energy density of the flash pulse. Thus the lower part of the SiC film is dissolved into the melted Si substrate, then during the solidification phase separation occurs and the SiC is recrystallized forming high quality 3C-SiC trapezoidal pyramids (TPs) on the backside of the non-dissolved SiC film. 1. However due to significant Si mass transport the Si-surface is seriously undulated. Also the SiC film is mainly improved from the backside, which cannot be used for further epitaxial growth. For these reasons an improved method was developed with the aim, to (i) minimize the undulations of the Si substrate, and to (ii) improve the quality of the SiC film at the front interface. This method involves the deposition of a silicon overlayer (SOL) onto the SiC, followed by an additional SiC layer on the SOL. The new method is called i-FLASiC where the “i” stands for “inverse”.

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.

The heterostructure formed by cubic silicon carbide/silicon (3C-SiC/Si) is very promising as substrate for cubic III-N growth and for SiC devices. Optimized Si substrate carbonization process before the epitaxial growth of SiC, leads to a higher quality of the layer. In this paper, transmission electron microscopy is used to analyze the defect morphology and strain of SiC layers grown by chemical vapor deposition on two differently carbonized substrates, with tensile and compressive strain state. Misfit dislocations, stacking faults and antiphase domains are observed in this heteroepitaxial system. Irrespective of the substrate used, the epitaxial relationship between Si and SiC is good. However, the grain misorientation of the mosaic structure and the strain of the overgrowth layer depend drastically on the carbonization conditions of the silicon substrate.

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.

Due to the large difference in lattice parameters and thermal expansion coefficients, the hetero-epitaxial growth of 3C-SiC on Si mainly results in highly defective layers on strongly bent wafers. The defects may not be detrimental for very basic applications, but the bow is. In order to solve this problem, we have developed a technique called checker-board carbonization which, basically, balances a compressive (interfacial) stress by a tensile one. In this way, the overall bending is effectively reduced. In this work, we will report on the effect of polishing the thick, as-grown, 3C-SiC layers deposited on top and results from, both, infrared and Raman spectroscopy collected on 35 mm diameter wafers will be presented. From DDX and low temperature photoluminescence measurements, we will show that a similar 3C-SiC quality can be achieved on, both, parts of the initially compressive and tensile re-grown layers.

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.

The so-called VLS (Vapour-Liquid-Solid) mechanism in an Al-Si melt has recently demonstrated the capability to grow at low temperature single crystalline 4H-SiC layers, with a high Al content. Using the newly developed VLS technique, we have deposited several 4H-SiC layers and determined the incorporated Al level by SIMS (Secondary Ion Mass Spectroscopy). Depending on the sample, we have found that the SIMS doping level ranges from 5 × 1019 to 1 × 1021 at.cm–3. This is the highest value reported so far for in-situ doped SiC:Al. From TEM (Transmission Electron Microscopy) analyses we show that the layers are single crystals, with a high density of defects at the lower interface but no foreign phase inclusion. These results compare well with the ones obtained in previous works using alternative doping techniques, like ion implantation, chemical vapour deposition or sublimation. It thus suggests that Al solubility limit in SiC is rather temperature independent. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The growth features of the nitrogen incorporation into GaAs grown by metalorganic vapour phase epitaxy (MOVPE) are presented, with a comparison between experimental results and a kinetic model. The so-called ‘distribution coefficient’ of nitrogen varies in the range 180–1000 depending essentially on growth temperature. Experimental results were analysed with a schematic process of surface reaction kinetics for controlling the mass transfer. Some kinetic rate constants are proposed. The modelling of N incorporation at 520–560°C allows an identification of species coming from the DMHy thermal decomposition. Surprisingly, this study shows that the rate of N incorporation weakly depends on the arsenic precursor at low growth temperatures.

Optical studies of GaAs1−xNx/GaAs and BxGa1−xAs/GaAs epilayers grown by metal organic chemical vapour deposition (MOCVD), with various nitrogen (N) and boron (B) compositions, have been achieved by photoluminescence spectroscopy (PL) as a function of the excitation density and the sample temperature (10–300 K). The experiments have shown that the GaAsN PL band emission presents a more significant red shift than the BGaAs emission. For the GaAsN a reduction of 110 meV/1%N is shown, but for the BGaAs the PL band emission shifts to the low-energy side by up to 2.5%. A more significant blue shift of the PL bands with increasing the excitation density has been observed for GaAsN compared to BGaAs epilayer structures. The temperature dependence of the PL peak energy has shown S-shaped behaviour for both structures, but the localisation effects are more important in GaAsN than in BGaAs. Based on these experimental results, it is shown that B incorporation does not cause large modification of the band structure in BxGa1−xAs alloys compared to pure GaAsN structures.

We report an experimental investigation of the growth and characterization of low-doped 4H-SiC epitaxial layers deposited on a-cut 4H-SiC substrates. The growth was carried out using standard procedures for optimized {0,0,0,1} 4H-SiC surfaces. The resulting sample thickness was 6-10 mum and, excepting few pyramidal defects, the surface was mirror-like with AFM surface roughness similar to 0.6 nm. Optical investigations have been done using, both, micro-Raman scattering and low temperature photoluminescence spectroscopy. They show a low level of residual doping with only nitrogen and aluminum acting as impurity. Electrical investigations confirm these results.