Silicon carbide layers were grown by solid source molecular beam epitaxy on silicon (111). Prior to the silicon carbide growth different amounts of germanium were predeposited on the silicon surface. Structural and morphological investigations with reflection high energy electron diffraction, x-ray diffraction, atomic force microscopy and spectroscopic ellipsometry revealed an improvement of the surface and interface properties for Ge coverages around and below 1 ML. The improved structural properties of the heterojunction lead to an amendment of the forward and reverse properties of the SiC/Si heterojunction.

Structures grown using the technique of molecular-beam epitaxy during deposition of carbon and/or germanium atoms on an Si(111) surface were investigated experimentally and theoretically. Experimental profiles of in-depth component distribution were obtained using SIMS-profiling, whereas a complex technique of computer simulation taking into account diffusion and ballistic processes was applied for the calculated profiles.

In this work nanostructures based on a 30 nm thick 3C-SiC (100) heteroepitaxially grown on Si(100) are demonstrated. They consist of free standing nanoresonators with dimensions below 50 nm. The free standing nanostructures and resonators were defined by electron beam lithography using hydrogen silsesquioxane (HSQ) as a negative tone e-beam resist acting as a selective etching mask during the anisotropic and isotropic dry etching. The influences of the proximity effect, the crystallographic orientation, the angle of exposing on the feature size are highlighted.

In the present paper we simulate the processes accompanying the SiC/Si epitaxial growth. The model suggested describes the formation and growth of voids at SiC/Si interface. These voids are sources of Si atoms for SiC growth. According to the model the size distribution function was obtained being in good agreement with experimental data. The influence of surfactants on the nucleation and growth of SiC nanoislands on Si was studied as well.

Isotropic etching of silicon carbide was achieved using a capacitive coupled parallel plate reactor in plasma etching mode and SF6 at elevated substrate temperatures. It was observed to be remarkable at substrate temperatures above 350°C. The influence of chamber pressure, masking materials, rf-power and substrate temperature were analyzed. Thereby, 8.5° off-axis oriented 4HSiC wafers exhibit a larger vertical and lateral etching rate compared to on-axis oriented SiC wafers. Additionally, the erosion of nitrogen containing masking material results in a reduction of the etching rates.

In2O3 nanoparticles were deposited by low-temperature metal organic chemical vapor deposition. The response of 10-nm thick In2O3 particle containing layers to NOx and O2 gases is investigated. The lowest detectable NOx concentration is ∼200ppb and the sensor performance is strongly dependent on the gas partial pressure as well as on the operating temperature. The sensor response towards 200ppm of NOx is found to be above 104. Furthermore, the cross-sensitivity against O2 is very low, demonstrating that the In2O3 nanoparticles are very suitable for the selective NOx detection.

The NOx and O2 sensing properties of highly textured indium oxide In2O3 thin films grown by metal organic chemical vapor deposition (MOCVD) technique have been investigated as a function of the operation temperature and partial pressure. The sensor is very sensitive to NOx and its response is strongly dependent on the gas partial pressure and operating temperature. The responses to NOx and O2 have been found to be maximal at 150°C. The optimum detection temperature for NOx occurs in the range 150–200°C considering the response and recovery times. In this range a very low response to O2 is observed indicating that the sensor is very suitable for selective NOx detection.

In 2 O 3 nanoparticles were synthesized at low substrate temperatures by the metal organic chemical vapor deposition technique. Nanoparticles with a mean diameter from 3 to 33 nm can be obtained by varying the growth temperature. Photoreduction and oxidation studies were carried out for particle-containing layers exhibiting a resistance change of more than five orders of magnitude after ultraviolet irradiation and oxidation by ozone. A grain boundary model was proposed to understand the photoreduction and oxidation mechanism for the nanoparticle layers. It was suggested that by photoreduction the nanoparticles are reactivated throughout the layer. The Schottky barrier between the nanoparticles decreases inducing a reduction of the space-charge-limited region. After oxidation, a completely depleted space-charge region covering the whole volume of In2O3 nanoparticles is formed. Furthermore, the bulk diffusion process dominates the response of thick layers during the oxidation process. By decreasing the layer thickness down to 10 nm, surface effects dominate, resulting in an ultrafast response to changes in ozone concentration. The typical response time of very thin In2O3 nanoparticle layers was determined to be less than 1 s.

Depletion-mode 4H-SiC field effect transistors (FETs) responding down to 0.002mbar of NOx gas at a temperature of 300°C were realized. A mixture of indium oxide (InOx) and vanadium oxide (VOx) was deposited by RF magnetron reactive sputtering as a gate material. The responses to NOx, D2, and O2 gases were investigated as a function of the operating temperature for different partial pressures of the test gases. The sensor is very sensitive to NOx and its performance is strongly dependent on the gas concentrations and operating temperature. The response to D2 has been found to be maximal at room temperature. The optimum detection temperatures occur in the range 275–325°C for NOx with these catalysts. The response to both O2 and D2 is very low in this temperature range, suggesting that the sensor is very suitable for selective detection of NOx. The optimum temperature of operation for detection of D2 is determined to be between 25 and 100°C. In this range no significant responses to O2 and NOx are observed, indicating that the sensor is very suitable for D2 detection at very low temperatures.

There is a high demand for compact low-cost ozone sensors. It has been shown recently that In2O3 nanolayers can act as ozone sensitive films activated at room temperature by ultraviolet light. In the present work, the authors integrate ultrathin layers of In2O3 nanoparticles and a GaInN∕GaN based blue light emitting diode (LED) on a single sensor chip. The integrated sensor was found to be sensitive to O3 concentrations as low as ∼40ppb. These results demonstrate that by integrating GaInN∕GaN based blue LEDs and metal oxide sensing layers back to back on a single chip, compact and robust gas sensors can be realized.

We have fabricated depletion-mode 4H–SiC field effect transistors (FETs) for use as gas sensors. To enable sensitivity to NOx and O2 gases, a mixture of indium oxide (InOx) and tin oxide (SnOx) was deposited by rf magnetron reactive sputtering as a gate material. The chemical composition of the deposited film was examined using Auger electron spectroscopy (AES) combined with depth profiling analysis. The response to NOx and O2 gases was investigated as a function of operating temperature for different concentrations of the test gas. The maximal response to NOx and O2 was observed at 350 and 400°C, respectively.

In 2 O 3 (001) thin films were grown on (0001) sapphire by metal-organic chemical vapor deposition. Highly textured ln 2 O 3 films were tested as ozone sensors based on the photoreduction and oxidation effects. The sensors were found to have the largest sensitivity at room temperature. With such ln 2 O 3 based sensors, the ozone concentrations in a wide range from 15 ppb up to 92 ppm were measured.

Phase selective growth of rhombohedral and cubic indium oxide polytypes was studied. The selective growth of different polytypes was achieved by adjusting substrate temperature and trimethylindium flow rate during metal organic chemical vapor deposition on c-plane sapphire. The optical band gaps of the cubic and rhombohedral phases were determined to be ∼3.7 and ∼3.0eV, respectively. On the basis of the performed structural investigations, a phenomenological model of the nucleation and growth of highly textured cubic In2O3 on Al2O3 (0001) is proposed.

Flash lamp annealing of multilayer stack of the type SiC/Silicon overlayer(SOL)/SiC reduces the defect densities in the 3C-SiC/Si heteroepitaxial structure. Ge and C additions to the SOL lead to a substantial increase of the mass transfer from the upper layer to the lower SiC layer. If the Ge content of the SOL and the flash lamp annealing conditions are properly chosen a homogeneous layer with a 3C-SiC thickness between 150 and 200 nm can be achieved corresponding to a growth rate between 7.5 and 10.0 +m/s. The thickening of the lower layer depends on the SOL composition. Ge and/or C incorporation into the SOL and therefore into the Si melt enhances the mass transport from the upper SiC layer to the lower one.

3C-(Si1-xC1-y)Gex+y ternary alloys were grown on 8.5° off axis 4H-SiC substrates by solid source molecular beam epitaxy in a temperature range between 750°C and 950°C. Energy dispersive X-ray (EDX) analysis revealed a decrease of the Ge incorporation versus substrate temperature. This effect is due to the fixed Si/Ge ratio during the epitaxial growth. The Ge distribution within the grown epitaxial layers was found to be nearly homogeneous. The investigations by atomic location by channeling enhanced microanalysis allowed the conclusion that Ge is located mainly at Si lattice sites.

An alternative route to improve the epitaxial growth of 3C-SiC(100) on Si(100) was developed. It consists in covering the silicon wafers with germanium prior to the carbonization step of the silicon substrate. Transmission electron microscopy and μ-Raman investigations revealed an improvement in the residual strain and crystalline quality of the grown 3C-SiC layers comparable to or better than in the case of 3C-SiC grown on silicon on insulator substrates. These beneficial effects were reached by using a Ge coverage in the range of 0.5–1 monolayer.

In this work, 120 nm cubic SiC layers have been grown on Si (111) by SSMBE, depositing 1ML of Ge at different temperatures before carbonization. In every case, SiC was epitaxially grown on Si (111) showing characteristic defects and more relaxation than a reference sample where Ge was not employed. Depending on the temperature of Ge predeposition, a reduction of voids or stacking faults was achieved. The residual strain depended on this temperature, as was confirmed by electron diffraction and infrared ellipsometry measurements.

In this work we evaluate the strategy of using 3C-SiC as a substrate for III-V nitrides heteroepitaxy (AlN, GaN…). Our methodology is based on the elasticity theory of strained interfaces and involves not only geometric parameters of host materials but also parameters related to their elastic properties. The basic physics involved in the theory correlates lattice dynamics and strain gradients via effective elastic constants associated with the host materials forming the heterosystem (S factor). Within this approach, the optimization of the IIIV/ 3C-SiC interface is achieved by applying, at the interface, continuity conditions to the host material S factors and the related geometric features. An alloyed layer, i.e. Al x Ga 1−x N, simulates the III-V compound. We find out that the optimizing composition of this layer is x=1 corresponding to a stoechiometric AlN layer. This is consistent with the result showing that AlN presents the closest structural characteristic to SiC. Our results also predict that, when used as a buffer layer, AlN may provide a mean to optimize the GaN/SiC interface.

We studied the interaction of elemental carbon with Si(111) and Si(100) surfaces with in situ real time spectroscopic ellipsometry at different C exposures ranging from 7 x 10(12)-7 x 10(14) cm(-2) s(-1) at 750 degrees C under UHV conditions in a molecular beam epitaxy equipment. The optical investigations were accompanied by real time RHEED studies. Using an optical three layer model (surface roughness, SiC layer, interface) on Si substrate the ellipsometric response allowed us to determine and quantify the different stages of the process: the nucleation, the coalescence, the growth kinetics, and the surface and interface evolution. The SiC film growth depends on C exposure and weakly on substrate orientation. The results obtained were compared to the RHEED observations. (C) 2000 Elsevier Science S.A. All rights reserved.

The interaction of ethene with silicon (111) surfaces at different process temperatures (580°C, 680°C, 780°C) was monitored in situ by spectroscopic ellipsometry. It is shown that spectroscopic ellipsometry is a reliable method to monitor the carbonization process of silicon surfaces. Different SiC formation stages (incubation time, √3×√3)R30° reconstruction, 2D growth and 3D growth) were observed using complimentary analyzing techniques. The change of the ellipsometric signal as a function of process time is related to these stages and was interpreted using an optical model which consists of four layers (surface roughness, SiC layer, interface layer, Si substrate).