Heteroepitaxial diamond

Formation of twin structures on the faces of diamond crystals and films have also been studied by Koidl s group in the early stage of diamond film research [84], So, we begin with reviewing their works, which is then followed by studies of other groups. To make heteroepitaxial diamond films, it is necessary to avoid the formation of twins, and thus the studies on the formation mechanism and morphology of twins are of great importance. 

In Ref. [257], Sii- Cx alloy films with x< 0.1 were deposited on Si by molecular beam epitaxy (MBE) to use them for the substrates of heteroepitaxial diamond films. It was expected that when x = 4.33%, a perfect lattice match of Sii C c D = 2 3 occurs and the degree of orientational alignment could be improved. An EIOD film, grown to a thickness of 20 pm using the BEN process, successfully resulted in a (100)-oriented film with (100) faces at the film surface, but the FWHM of the (111) XPF was 6°, the same value as when the direct nucleation of diamond was done on Si using BEN. The results of Raman spectroscopy and XRD of the diamond films were not dependent on the x value. It was thus confirmed that the orientational characteristics of the HOD films had no significant dependence on the C content of the Sii C,v layers. This work can be compared with that of Ref. [258], where layers with x= 1.4 and 3.5% were deposited on Si(lOO) by... 

Figure 12.6. Schematic diagram on heteroepitaxial diamond growth on Pt(lll) [383].

Most recently, heteroepitaxial diamond films were deposited on Ir(lOO)/ a-sapphire 1120). The orientational relationships between Ir and a-sapphire, and diamond and Ir were as follows Ir 100 //Al203 1120, lr[011]//Al203[ll00], D 001 //Ir 001 and D[100]//Ir[100]. The heteroepitaxial area was 50mm [410, 411]. 

So far, growth processes of oriented diamonds and diamond films have been reviewed by focusing on the process conditions. In this section, properties and applications of heteroepitaxial diamond films thus produced will be reviewed. 

The electrical properties of single crystal diamond will be useful to study those of heteroepitaxial diamond films. As a reference. Figures 13.1 (a)-(c) show the resistivity, mobility, and carrier density of single crystal diamond as a function of temperature [107]. Figures 13.2 (a) and (b) are the resistivity and mobility as a function of the carrier density. A more thorough study on B-doped homoepitaxial diamond is presented in Ref. [416], where AFM observation of the layer surface. Hall measurements at different temperatures, and other data are presented. 

Figure 13.23. Field emission properties from a heteroepitaxial diamond film grown on Ir(lll). The inset shows the experimental setup [442],...

Among diamond films with various morphologies, HOD and heteroepitaxial diamond films will provide us with the best material for highest value-added, high performance applications. In this sense, the works reviewed in this monograph have given a great contribution. 

Table E.l. Crystal structures of diamond and substrate materials for heteroepitaxial diamond growth (data taken from Ref. [205]).

The primary difficulty inherent in this issue is the small niunber of materials with suitable crystal structures and lattice constants. Some transition metals and ceramics, such as Ni, Cu, Fe, and cBN (Table 5, Ch. 3), are the few isostructural materials with sufficiently similar lattice constants (mismatch <5%). In addition, the extremely high surface energies of diamond (ranging from 5.3 to 9.2 J m for the principle low index planes) and the existence of interfacial misfit and strain energies between diamond films and non-diamond substrates constitute the primary obstacles in forming oriented two-dimensional diamond nuclei. Earlier attempts to grow heteroepitaxial diamond on the transition metals were not successful. The reasons may be related to the high solubility/ mobility of C in/on the metals (for example, Fe, Co, or the... 

Heteroepitaxy of diamond on cBN powder has been achieved by Yarbroughl l and others. Heteroepitaxial diamond films, 0.7 to... 

X. Jiang, K. Schiffmann, A. Westphal, and C. P. Klages, Atomic-force-microscopic study of heteroepitaxial diamond nucleation on (100) silicon, Appl. Phys. Lett, 63(9) 1203-1205 (1993)... 

Figure 7. SEM micrograph of a heteroepitaxial diamond film obtained on (001) silicon by bias-induced nucleation, film thickness s=6.5pm. Vertical and horizontal edges of the photograph are orientated parallel to the Si [110] and [ilO] directions, respectively (by courtesy of X. Jiang).

The most important crystallographic surface of CVD diamond is the (100) surface. Quasi-heteroepitaxial diamond films with smooth (100) surfaces can meanwhile be deposited on siHcon [65], silicon carbide [66], or iridium [67]. Also, the homoepitaxial growth of diamond is much less susceptible to the incorporation of stacking faults or creation of twin crystals in case of (100) as compared to (111). The (100) surface as illustrated in Figure 10.6 reflects the cubic symmetry of the lattice along the 100 direction. The top three atomic layers are shown in the figure along with... 

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