L. Imhoff

Thermal effects on the growth by metal organic chemical vapour deposition of TiO2 thin films on (100) GaAs substrates

Abstract TiO 2 thin films were deposited on (100) GaAs substrates by LP-MOCVD with deposition temperatures ( T d ) ranking from 450 to 750 °C. The structure of these layers was studied by X-ray diffraction (XRD) and Raman spectroscopy. The growth of the TiO 2 anatase phase was observed for T d T d >600 °C. Finally, X-ray photoelectron spectrometry (XPS) and secondary ion mass spectroscopy (SIMS) experiments showed the presence of small quantities of Ga and As through the whole film thickness, slightly increasing at the surface of the layers. This result was related to the SEM observations and explained by considering the growth conditions.

Coexistence of several structural phases in MOCVD TiO2 layers: evolution from nanometre to micrometre thick films

The morphology and the structure of TiO2 films, grown on Si (1 0 0) substrates by metal organic chemical vapour deposition (MOCVD) was investigated in 5–500 nm thick films. It was shown that the TiO2 layer is mainly amorphous at the first stages of deposition. The growth of nanocrystallites begins inside the amorphous TiO2 layer, and it continues at the expense of the amorphous phase until the crystallized grains occupy the whole layer. Then, the film growth continues with a columnar structure. The coexistence of anatase and rutile phases was evidenced from the beginning of the growth by high resolution transmission electron microscopy and grazing incidence x-ray diffraction. However, the anatase growth overcomes that of rutile, leading to an inhomogeneous phase distribution as a function of the film thickness.

Elaboration and characterization of barium silicate thin films

Room temperature depositions of barium on a thermal silicon oxide layer were performed in ultra high vacuum (UHV). In-situ X-ray photoelectron spectroscopy (XPS) analyses were carried out as well after exposure to air as after subsequent annealings. These analyses were ex-situ completed by secondary ion mass spectrometry (SIMS) profiles and transmission electron microscopy (TEM) cross-sectional images. The results showed that after air exposure, the barium went carbonated. Annealing at sufficient temperature permitted to decompose the carbonate to benefit of a barium silicate. The silicate layer was formed by interdiffusion of barium with the initial SiO2 layer.

Structural characterization of TiNxOy/TiO2 single crystalline and nanometric multilayers grown by LP-MOCVD on (110)TiO2

TiO2/TiNxOy superlattices were grown by Low Pressure-Metal-Organic Vapor Phase Epitaxy (LP-MOVPE) technique at deposition temperatures ranking from 650 to 750°C. The growth was performed on top of TiO2(110) rutile substrates. Intense peaks observed in the X-rays rocking curves and θ-2θ diffraction patterns show the presence of crystalline epilayers. The TiNxOy layers were grown in a (200) cubic structure on the (110) quadratic TiO2 epilayer structure. Transmission electron microscopy confirmed the XRD results and showed the formation of periodic and well structured epilayers.

Structural and in depth characterization of newly designed conducting/insulating TiNxOy/TiO2 multilayers obtained by one step LP-MOCVD growth

Abstract TiNxOy/TiO2 multilayers have been grown by LP-MOCVD using titanium isopropoxide (TIP) precursor during the whole growth, but with an ammonia flow interrupted for the TiO2 layers. The one step growth process used to grow these structures allowed to stack the conducting and insulating layers without any growth breakdown. SIMS and TEM analyses showed the presence of an alternated insulating/conducting layers structure. Moreover, electrical measurements allowed to measure the dielectric part of insulating TiO2 stacked in these structures, whose permittivity was found to be about 80 for a MOS structure. Thus, such multilayers may lead to very promising applications in the microelectronics field.

Novel three dimensional Ga structures on GaAs (100) substrates obtained by MOVPE

Novel three dimensional (3D) gallium structures are presented by using commercial organometallics and conventional metal−organic vapour phase epitaxy system (MOVPE). These 3D structures grow up naturally on GaAs substrates and their shapes depend on the growth conditions and principally on the growth temperature. Introduction The (Ga, Al, In)N system represents a very important kind of materials for optoelectronic visible devices applications (1). Shortening the size of optoelectronics devices is an important step within the industrial application and its improvement (2). Gallium metal−organic (TMGa) precursor was used to allow for the growth of these structures. The growth temperature was varied between 500 to 750 °C and the reactor pressure varied between 100 to 760 torr. Nitrogen was utilized as carrier gas. Reactor growth conditions can be found elsewhere and commercial organometallic gallium precursors can be used as well (3). Results By using the MOVPE conventional conditions many 3D Ga structures were obtained : montgolfier, cylinder, scepter and cauli−flower like structures (Figure 1). The morphology depends principally on the growth temperature and substrate surface conditions. These structures stick to the substrate by a very thin base. Micrometer structure size can be obtained (.1 to 5 μm diameter). The montgolfier point density at 650 °C is around 10 /cm. 3D Ga selective growth could also be obtained principally on line substrate defects (fig. 1c). EDX elemental analysis results show that these 3D structures are mainly gallium composed (fig.2). It should be noticed that, for these experiments, silicon was used as a substrate instead of GaAs in order to get rid of any interference with gallium from the substrate. Moreover it was evidenced using X−ray diffraction (XRD) that these gallium structures are meta−stable gallium phases as presented in figure 3 (4). Conclusion This paper presents the growth and characterization of novel Ga metallic 3D structures, obtained by the conventional MOVPE technique. To support this 3D Ga structures, GaAs (100) substrates were utilized. These 3D structures can be suitable for nitrogen incorporation to obtain GaN like structures (5, 6). 10th European Workshop on MOVPE, Lecce (Italy) 8−11 June 2003 PS.VI.15