ZnO Growth

Fig. 6.3. DEZ consumption Cdez, i.e., percentage of DEZ effectively used for ZnO growth, as a function of the pressure in an LP-CVD chamber, for which DEZ and water vapors are used as precursors...

In the CVD process, the substrate temperature is a key parameter by heating the substrate, one supplies, directly to the growing surface, additional energy that favorably influences the specific chemical reactions that lead to ZnO growth. 

As the speed of the reactions at the growing surface is increased when the temperature is raised, a temperature-dependent growth rate should basically be observed for LP-CVD process. In Fig. 6.19, the deposition rate and the consumption of DEZ (defined as the percentage of DEZ effectively used for ZnO growth, the rest of DEZ being pumped out of the chamber) are shown as a function of the substrate temperature for the LP-CVD process developed at IMT Neuchatel, which operates at 0.5mbar and uses DEZ and water vapors as growth precursors. 

The role of some additional species as Zn, Fe, Cu, C and H2, in the ZnO growth by vapor transport, can be interpreted in this framework. These species would produce a Zn excess, either directly or from an O2 consumption. 

Figure 1 shows cross-section TEM images of a MOVPE-grown ZnO layer on Al203(0001) with a 40 nm GaN buffer layer deposited prior to the ZnO growth. Isopropanol and Diethylzinc were used as precursors for the ZnO deposition with a Vl/II-flux ratio of 36 at total reactor pressure of 400 mbar and hydrogen as a carrier gas. The substrate temperature was 380 °C. 

Abstract Most of the ZnO growth techniques result in -type conductivity of the crystal,... 

The complex structure of the ZnO/Si interface has also directly been observed in cross-sectional TEM micrographs. An example is given in Fig. 5. This micrograph clearly reveals the formation of a thin amorphous fdm on the Si-surface (suboxide phase), the formation of nano-crystalline phases followed by columnar ZnO growth. ... 

An example of polarity determination and its application is the study of the growth mechanism of ZnO nanowires. During ZnO growth, asymmetric side growth is... 

Finally, the selective growth of inorganic crystals was demonstrated on a SAM-templated silver surface. Hsu and coworkers [58] preferentially grew zinc oxide (ZnO) from an aqueous solution on silver surfaces. The silver surface was patterned by 4CP with a carboxyl acid (-COOH)-terminated SAM to inhibit ZnO growth. Figure 5.5.9(b) and (c) contain micrographs that demonstrate ZnO growth only... 

Figure 9.9. (a) TEM images of ZnO growth on mineralization peptide-coated F877 triple helices, (b) Photoluminescence spectrum of (a). 

As alluded to earlier, ZnO is widely used in thin-film form deposited on normative substrates. Therefore, the material quality, actually properties in general, of the ZnO films depends on the properties of the substrates used. Especially, the lattice parameters and thermal expansion coefficients of these substrates are extremely important since reduction of strain and dislocation density in ZnO thin films is the main objective, and substrates with parameters similar to those of ZnO are favorable in this context. Thermal expansion coefficients of various substrates used for thin-film ZnO growth are given in Table 2.3. 

Because ZnO thin films deposited on foreign substrates are used in different applications, thermal conductivities of the substrates would be of concern when designing device structures. A comparison of thermal conductivities for various templates used for ZnO growth is provided in Table 2.3. 

To reduce the strains and dislocation density in epitaxial ZnO and related films, closely lattice-matched substrates are favored for growth. Sapphire substrates are commonly used for ZnO heteroepitaxial growth, primarily on the (0001) orientation (basal or c-plane), and also on the (11 20) o-plane. In addition, ZnO and related oxides have been grown on Si [20], SiC [39], GaAs [21, 22], Cap2 [19], and ScAlMg04 [23]. Lattice parameters of several substrate materials frequently used for ZnO growth and their mismatch to ZnO are listed in Table 2.3. 

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