J. Pezoldt

Cubic GaN epilayers grown by molecular beam epitaxy on thin β-SiC/Si (001) substrates

The molecular beam epitaxy of cubic GaN on Si(001) substrates, which were covered by a 4 nm thick β-SiC layer, is reported. The structural and optical properties of the cubic GaN epilayers were studied by transmission electron microscopy, high-resolution x-ray diffraction, and low-temperature photoluminescence measurements. We find clear evidence for the growth of cubic GaN layers almost free of hexagonal inclusions. The density of extended defects and the near band edge photoluminescence of the cubic GaN layers grown at substrate temperatures of 835 °C is comparable to that of high quality cubic GaN epilayers grown by molecular beam epitaxy on GaAs (001) substrates.

SiC voids, mosaic microstructure and dislocations distribution in Si carbonized layers

Abstract The defect structure of SiC/Si layers obtained by carbonization of Si is reported by means of transmission electron microscopy in high-resolution (HREM) and conventional (CTEM) modes. 3C–SiC was obtained after a rapid thermal annealing treatment and good interfacial quality is reported in terms of small void dimensions and densities. Moreover, high misfit dislocation densities are observed close to the Si/SiC interface and inside the SiC layer without observable generation of threading dislocations. The mosaic grain structure is also evidenced, with low misorientation with respect to the substrate. These results are encouraging for further growth of III–N alloy heterostructures.

Effective collection and detection of airborne species using SERS-based detection and localized electrodynamic precipitation.

Three different delivery concepts (standard diffusion, global electrodynamic precipitation, and localized nanolens-based precipitation) and three different SERS enhancement layers (a silver film, a nanolens-based localized silver nanoparticle film, and the standard AgFON) are compared. The nanolens concept is applied to increase the SERS signal: a factor of 633, when compared to a standard mechanism of diffusion, is observed.

Chemical conversion of Si to SiC by solid source MBE and RTCVD

Abstract The carbonization of (111)Si surfaces exposed to a sublimed carbon molecular beam with carbon fluxes varying ca two orders of magnitude at substrate temperatures between 700 and 1050°C was studied. The structural and morphological evolution was investigated in comparison to the growth under RTCVD conditions. Two different polytype structures, 3C- and 2H-SiC, were grown on 4″ (111)Si wafers. Generally in the investigated parameter range carbonized layers formed by RTCVD have a better crystallinity and a smoother surface.

Aluminium implantation of p-SiC for ohmic contacts

Abstract An important problem is the formation of low-resistance ohmic contacts, especially for p-type SiC. The deposition of all known metals onto p-type SiC will always result in a depletion p-type contact. To obtain an ohmic contact, the depletion zone has to be smaller. This may be achieved by very shallow p-dopant implantation. Another aim of this research was to study the structural and chemical changes of the surface, as well as the interface and bulk after implantation, annealing and contact formation. Specific contact resistance of 5 × 10−4 Ω cm2 was achieved on p-implanted 6H-SiC with Al Ti metallization.

The deposition of aluminum nitride on silicon by plasma-enhanced metal-organic chemical vapour deposition

Abstract Aluminium nitride (AlN) films were deposited by electron cyclotron resonance plasma-enhanced chemical vapour deposition using trimethylaluminum (TMA) as precurser at temperatures from 25 to 600 °C and at different concentrations of TMA. Adhesive layers with a thickness ranging from 100 to 200 nm and a refractive index of 1.65–2.0 are obtained. By Auger electron spectroscopy, reflectum high energy electron diffraction and ellipsometric measurements at 632 nm we found in all layers a high oxygen concentrations only slightly dependent on the deposition conditions. A quadrupole mass spectrometer was used to investigate the composition of the gas phase. The gas spectra did not indicate partial pressures of oxygen and water. Sputtering effects and plasma chemical etching of the microwave window made of quartz glass seem to be the source for the incorporated oxygen.

A growth model for the carbonization of silicon surfaces

Copyright (c) 1997 Elsevier Science S.A. All rights reserved. The kinetics of carbonization of (111)Si by rapid thermal processing with C 3 H 8 diluted in H 2 were investigated and compared with published results on (100)Si. A mathematical description for the saturation behaviour was developed and fitted with the data received by ellipsometry and atomic force microscopy. These parameters are nucleation density, silicon diffusion flux and a ratio between vertical and horizontal growth. The model agrees in the estimation of saturation thickness and time as a function of concentration and temperature. A boundary concentration around 0.1% was found where the surface is already sealed off after heating up. Above this concentration the model failed.

Deposition of aluminium nitride films by electron cyclotron resonance plasma-enhanced chemical vapour deposition

Abstract An electron cyclotron resonance plasma source was used for the deposition of aluminium nitride (AlN). AlN films were grown using trimethyl aluminium in hydrogen as carrier gas and nitrogen or ammonia as a nitrogen source onto silicon, glass and steel substrates. The deposition temperature was ranging from 200 to 600°C, the microwave power was varied from 250 to 400 W and the operation pressure was (1–4) × 10 −3 mbar. Atomic composition of the samples was investigated by Auger electron spectrometry and Fourier transform IR spectrometry and mechanical properties were investigated by a dynamic force-penetration method and scratch test. The influence of the deposition parameters on the structure and hardness were investigated. The incorporation of oxygen into the AlN films after the deposition is caused by diffusion of water along the grain boundaries of textured layers. Universal hardness of 10 000 N mm −2 and critical loads up to 42 N were found for AlN coatings on steel substrates.

Real time spectroscopic ellipsometry monitoring of the SiC growth during the interaction process of elemental carbon with Si surfaces

Abstract 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 7×10 12 – 7×10 14 cm −2 s −1 at 750°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.

α-SiC–β-SiC heteropolytype structures on Si (111)

Nanoscale α-SiC(0001) on β-SiC(111) heterostructures on Si (111) substrates fabricated by ultralow-pressure chemical vapor deposition are demonstrated. The intentional formation of the α-β structure was achieved by adjusting the SiH4 to C2H4 flux ratios to carbon rich conditions and by controlling the diffusion length. The developed method allows the formation of heteropolytypic structures with a controlled thickness of the intermediate cubic β-SiC layer.