Th. Stauden

Phase selective growth and properties of rhombohedral and cubic indium oxide

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.

Integration of In2O3 nanoparticle based ozone sensors with GaInN∕GaN light emitting diodes

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.

Initial stages in the carbonization of (111)Si by solid-source molecular beam epitaxy

Silicon carbide can be reproducibly grown on (111)Si below 600 °C by carbonization using an elemental solid carbon source in molecular beam epitaxy. The initial stages were observed by in situ reflection high-energy electron diffraction. Prior to silicon carbide growth, the continuous carbon flux lead to a transition from the (7×7) reconstruction of clean (111)Si to a carbon-induced (∛×∛)R30° structure. Above 660 °C, the silicon carbide growth starts directly on the silicon surface via three-dimensional nucleation. Below 660 °C, first a thin silicon–carbon alloy was formed by diffusion of carbon into the surface near the region with a concentration exceeding the bulk solubility in silicon.

The role of Si as surfactant and donor in molecular-beam epitaxy of AlN

The growth of Si-doped AlN(0001) thin films on Al2O3(0001) substrates by plasma-induced molecular-beam epitaxy is reported. We have found that Si positively affects the epitaxy being an effective surfactant for AlN growth with a remarkable impact on the crystal quality. It was proven that the characteristic surface reconstruction sequences frequently related to the Al adatoms are obviously Si induced on AlN(0001) surfaces. It was also observed that heavy doping conditions result in volume segregation of Si on the threading dislocation network and in the formation of an amorphous (AlO)(SiO)N cap layer caused by surface oxidation of the accumulated Al and segregated Si. The electron affinity was measured to be smaller than 0.5eV on the clean AlN surface after removing of the cap layer using Ar+ sputtering.

Ge-modified Si(100) substrates for the growth of 3C-SiC(100)

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.

Photoreduction and oxidation behavior of In2O3 nanoparticles by metal organic chemical vapor deposition

In2O3 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 t...

Investigation of the nucleation and growth of SiC nanostructures on Si

Using in situ reflection high energy electron diffraction (RHEED), ex situ atomic force microscopy (AFM) and transmission electron microscopy (TEM) the early stages of SiC growth on Si during the carbonisation were investigated in a solid source molecular beam epitaxy equipment. Different mechanisms of SiC precipitate growth by SSMBE were found. The SiC growth during carbonisation of Si(111) at 600°C is controlled by diffusion and at higher temperatures by a two-dimensional nucleation process, which is mononuclear at 660°C and polynuclear above 750°C. At temperatures greater than 750°C and 850°C three-dimensional nucleation occurs at (111) and (100) surfaces, respectively.

Influence of the heating ramp on the heteroepitaxial growth of SiC on Si

The influence of the heating rate on the initial growth of SiC on silicon by carbonization was investigated for two strongly differing methods: solid source molecular beam epitaxy and rapid thermal chemical vapour deposition. An improvement of the structural and morphological properties can be obtained by a two dimensional nucleation stimulated by a defined heating cycle in a (hydro-) carbon flux. This improvement is strongly associated with a decreased diffusion coefficient for silicon through the grown layer.

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.

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.