MOCVD technique

The most extensively studied of these complexes for use in CVD are the diethyldichalcogeno-carbamates [M(E2CNEt2)2] (M = Zn, Cd E = Se, S). These complexes are air-stable solids, and are dimeric in the solid state175,176 but monomeric in the vapor phase, as judged from mass spectra. Thin films of CdS, CdSe, ZnS, and ZnSe have been grown by a number of different MOCVD techniques using these complexes as single-source precursors they are listed in Table 11. 

In this work, Pradhan et al. demonstrated the encapsulation of crystalline Fe404 nanoparticles into the uniform carbon nanotubes by the MOCVD technique using ferrocene and that the size and number of such nanoparticles can be easily controlled by changing the MOCVD temperature or its period. At a proper MOCVD condition, Fe404 nanocrystals could be introduced into all of the nanotubes to different degrees, and more than 20% of the total volume of the tube hollow was filled with the nanoparticles. 

Mononuclear complexes in the cases when the number of donor atoms in the ligands is not less than is necessary for the saturation of the coordination sphere of the central atom. These compounds are of interest as molecular precursors of oxide materials in the MOCVD technique, such as,... 

The intensive development of the chemistry of homo- and heterometallic alkoxides of copper started more than 10 years ago in connection with the prospects of their application in the preparation of materials and initially in high temperature superconductors. In the search for the appropriate precursors in sol-gel and MOCVD techniques, attention was focused on the alkoxides of copper (I) and the fluorinated alkoxides of copper (II) — oligomeric derivatives soluble in non-polar solvents and existing not only in condensed but also in the gas phase. The derivatives of copper (II) and aliphatic alcohols, even rather branched or functional ones (such as alkoxyalkoxides) turned out to be polymeric substances uninteresting for further application. 

The MOCVD technique has also been used to deposit a number of refractory compounds for a wide range of applications. One of the advantages of this technique is the lower deposition temperature, which makes it very suitable for deposition on substrates, which are thermally sensitive, such as steels. Wear - resistant tungsten carbide coatings have been deposited on steel, using WF6 and suitable hydrocarbon gases at temperatures below 873 K.4,5... 

There have been relatively few metal-organic precursors reported for chromium materials. Cr(acac)3 and other diketonate derivatives have been employed for the growth of oxide phases by MOCVD techniques. " Cr(CO)6... 

MOCVD techniques for BST capacitor technology for next-generation ULSI DRAMs were reviewed. Although it has been proven that the material properties of BST films are good enough for DRAM applications, integration of the BST film into the devices requires further research, especially in terms of BST film deposition techniques and electrode fabrication technologies. 

Metalloorganic Chemical Vapor Deposition (MOCVD) Technique... 

Because of the growing importance of homo- and heterometallic alkoxides (3, 24) as precursors for ceramic materials by the MOCVD technique (cf. Section VIII), their mass spectroscopic studies should be very useful in ascertaining their applicability. 

Although MBE continues to be the best technique for controlled deposition of thin layers (10-100 A) of materials, the MOCVD process does offer the advantage for rapid deposition over large areas of substrates. The basic principles of the MOCVD technique is the thermal decomposition of volatile molecular precursors to the desired combined form (or even the constituent metal itself) on a selected substrate at not too high a temperature. In addition to the volatility of the precursor and its facile decomposition to the desired combined form for deposition, the whole operation should not, from the practical point of view, involve any toxic/hazardous byproducts, that might entail any environmental problems. 

Although metal alkoxides proved to be excellent precursors for the preparation of ceramics by the sol-gel process, their applications in the MOCVD technique are not as widespread, in spite of the attractive features of their volatility and tendency to decompose to the metal oxides. Both of these desirable prerequisites appear to be enhanced, as discussed earlier, by choosing more ramified alkoxide groups. Despite these attractive features, the MOCVD applications of metal alkoxides appear to be limited by (a) their commercial nonavailability, (b) handling difficulties arising from their ready hydrolyzability, and (c) the lack of a clear understanding of their decomposition pathways, which could lead to improvement(s) in the purity of the deposited material. 

Figure 83. Different steps involved in MOCVD technique.

Obviously, the lower oligomerization tendencies of the branched alkoxides of metals in valence states 5,4, and 3 endow upon them sufficient volatility to make them useful in the MOCVD technique. Generally however, the lower... 

Obtaining electrooptical thin films by MOCVD techniques has been less investigated, although volatile oxide precursors—alkoxides or 3-diketonates— exist for nearly all elements. For PbTiOs films titanium isopropoxide has been... 

III-V nitrides (InN, GaN and AIN) are made by CVD using (CH3)3M (M=In, Ga and Al) and NH3 as precursors [6]. HgCdTe, which is used in infrar (IR) detectors, is made by the reaction of the dimethyl derivatives of the metals [7]. PbSnTe is also synthesized by CVD [8]. High-quality thin films of superconducting YBa CUjO,. have been prepared by metal organic chemical vapour deposition (MOCVD) techniques using p-diketonate derivatives of Y, Ba and Cu as precursors [9]. 

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