Organometallic Chemical Vapor Deposition Technique Research Articles

Development of hydrogen-free fully amorphous silicon oxycarbide coating by thermal organometallic chemical vapor deposition technique

In this study, a dense fully amorphous (hydrogen-free) silicon oxycarbide (SiOC) coating was successfully deposited by thermal organometallic chemical vapor deposition (thermal MOCVD) technique using mixtures of liquid hexamethyldisiloxane (HMDSO) and ethanol. The nature of chemical bonding, microstructure and mechanical properties of the prepared coating were studied using field emission scanning electron microscopy (FESEM), scanning transmission electron microscopy (STEM), 29Si magic-angle-spinning nuclear magnetic resonance (MAS NMR), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and nano indentation techniques. The results showed that the prepared silicon oxycarbide coating is fully amorphous and it is composed of SiO4 and SiO3C structural units. The hardness (11.0 GPa) and elastic modulus (96.0 GPa) of the prepared coating were comparable or even better than other SiOC ceramic materials prepared by traditional high temperature processing techniques.

Characteristics of ZnO Nanowall Structures Grown on GaN Template Using Organometallic Chemical Vapor Deposition

Uniformly distributed ZnO nanowall network structures were grown at 550 degrees C by organometallic chemical vapor deposition technique on the GaN/sapphire substrate without using any catalysts. In this research, we discussed the nanostructures and optical properties of ZnO samples grown under the same conditions but on different underlying materials (GaN/sapphire and sapphire). By adjusting the growth parameters, ZnO nanowall networks with a honeycomb-like pattern without using any metal catalysts were successfully fabricated on the GaN/sapphire and sapphire substrates. Since the lattice mismatch between ZnO and GaN is only about 1.8% while the lattice mismatch between ZnO and sapphire is about 18.4%. Lattice mismatch may not be the decisive factor in the formation process of ZnO nanowall networks. The ZnO grown on GaN epilayer had smaller full width at half maximum value than that of ZnO grown under the same growth condition on the sapphire substrate, indicating a higher crystal quality in the sample of ZnO on GaN. The room temperature PL measurement of both ZnO nanostructures grown on GaN and sapphire show strong ultraviolet peak intensity and high intensity ratio of the near band emission to the deep-level emission in a PL spectrum.

Film texture evolution in plasma treated TiN thin films

In semiconductor technology, TiN thin film elements can be used as diffusion barrier between a metallic layer and a silicon oxide dielectric. Plasma application during the growth of TiN thin films modifies the microstructure of these films and consequently alters their physical properties. But details of the effect of plasma application on the evolution of the film microstructure and correlations between this evolution and the physical properties are still unclear. To clarify the correlations, the microstructure of a series of TiN thin films, deposited using an organometallic chemical vapor deposition technique combined with plasma treatments has been analyzed by transmission electron microscopy (TEM). The films were obtained by repeated fabrication sequences consisting of limited film growth followed by the application of a N2/H2 gaseous plasma with various powers and duration times and are actually stackings of plasma-treated elementary layers. TEM analysis shows that these films are made of nanocrystallites and that whereas crystallites are randomly oriented when no plasma is applied, short-time plasma treatments induce a tendency to 〈200〉 texture and longer treatments progressively rotate the direction of texture to 〈220〉.

Synthesis of CdSe quantum dot–ZnS matrix thin films via electrospray organometallic chemical vapor deposition

A modified organometallic chemical vapor deposition technique is used to incorporate luminescing II–VI nanocrystals (NCs) into ZnS thin films. The NCs are synthesized in organic solution and consist of a CdSe core and ZnS shell. The ZnS matrix is deposited by OMCVD from diethyl zinc and hydrogen sulfide while the NCs are delivered to the film surface via electrospray. Varying the size of the CdSe NC core enables tunable emission from the blue to the red. The ZnS shell provides electronic and chemical passivation of the CdSe core improving its luminescence and thermal stability. The thin films exhibit room temperature photoluminescence (PL) and cathodoluminescence (CL) dominated by emission from the NCs. PL quantum efficiencies greater than 10% have been achieved. The dependence of thin film luminescence and microstructure on deposition temperature is studied using optical photoluminescence and X-ray diffraction. Particular emphasis is placed on the relationship between the host ZnS structure and the optical properties of the NC–ZnS composite thin film.

Diffusion-enhanced epitaxial growth of thickness-modulated low-loss rib waveguides on patterned GaAs substrates

Rib waveguides have been fabricated without any post-crystal growth processing steps. The ribs are defined by the two nongrowth (111)B surfaces that develop at each edge of (011) mesas on a patterned GaAs substrate during organometallic chemical vapor deposition (OMCVD) of GaAs/AlGaAs structures. Propagation losses as low as 0.6 dB/cm at 1.52 μm wavelength have been obtained, which is attributed to the smoothness of the (111)B facets defining the GaAs guiding layer. This study revealed the importance of surface diffusion-enhanced crystal growth when a growth surface is adjacent to a nongrowth surface such as a (111)B facet. This effect was quantified here and its magnitude suggests that the OMCVD technique would be well suited for the growth of structures tapered in three dimensions, of interest for integrated optics applications.

GaAs/AlGaAs quantum wells and double-heterostructure lasers grown by chemical beam epitaxy

The growth system and growth kinetics of chemical beam epitaxy (CBE) are briefly described and its differences from molecular beam epitaxy (MBE) and organometallic chemical vapor deposition (OMCVD) are discussed. We characterize the capability of this technique in preparing high quality multilayer heterostructures by growing GaAsAl x Ga 1− x As single and multiquantum wells and double-heterostructure lasers. Studies using low-temperature photoluminescence and excitation spectroscopy techniques show that on the average the quantum wells are similar in quality to similar structures from the laboratory grown by MBE and in some important respects, superior to those grown by OMCVD. An interface roughness of δ L ≲± a/2, where a is the lattice constant, and very square wells (undistorted) even with continuous growth, in contrast to OMCVD, are inferred from the excitation spectra. Unusually sharp exciton transition peaks up to E 3h including forbidden transitions were obtained in single quantum wells. Such high quality lineshape has not been obtained in MBE- or OMCVD-grown wafers so far. The excitation spectra also show no evidence of band filling due to holes or electrons from the Al x Ga 1− x As layers which is a common problem with the OMCVD technique. From this study, it is also shown that the GaAs and Al x Ga 1− x As materials are of very high purity. The first GaAs/Al x Ga 1− x As double-heterostructure lasers grown by CBE is also achieved. Very low averaged current threshold densities of ≌ 500 A/cm 2 were obtained for wafers with active layer thicknesses of ∼ 500–1000 Åand confinement layers of Al 0.5Ga 0.5As. Such current threshold densities were similar to those obtained from the best wafers grown by other techniques. The present results unequivocally established that CBE is capable of producing high optical quality multi-layer heterostructures for state-of-the-art device applications.

Very high quality single and multiple GaAs quantum wells grown by chemical beam epitaxy

High quality GaAs/AlxGa1−xAs single and multiquantum well heterostructures were grown for the first time by chemical beam epitaxy. Studies using low-temperature photoluminescence and excitation spectroscopy techniques show that on the average these samples are similar in quality to similar structures from this laboratory grown by molecular beam epitaxy (MBE) and in certain specific characteristics superior to the MBE ones. Furthermore, in some important respects, they are also superior to those grown by organometallic chemical vapor deposition (OMCVD). The very small red shifts observed between emission and n=1 exciton transition E1h with continuous growth show that the emission is dominated by E1h excitons. An interface roughness of δL≲±a/2, where a is the lattice constant, and very square wells (undistorted) even with continuous growth, in contrast to OMCVD are inferred from the excitation spectra. Unusually sharp exciton transition peaks up to E3h including forbidden transitions were obtained in single quantum wells. Such high quality line shape has not been obtained in MBE or OMCVD grown wafers so far. The excitation spectra also show no evidence of band filling due to holes or electrons from the AlxGa1−xAs layers which is a common problem with the OMCVD technique. From this study, it is also shown that the GaAs and AlxGa1−xAs materials are of very high purity.