Transition metals in GaN

A8.7 Yellow luminescence in GaN A8.8 Hydrogen and acceptor compensation in GaN A8.9 3d transition metals in GaN and related compounds A8.10 Er-doped GaN and AIN... 

In AIN crystals, transition metal PL appears at about the same energetic position as in GaN. In TABLE 1 we summarise 3d transition metal emissions identified in AIN and GaN and corresponding references. The transitions are listed in the last column. It seems that 3d transition metals detected in GaN are generally detected in AIN at nearly the same energetic position. This indicates that the bonding between the four nitrogen ligands and the 3d transition metals in GaN and AIN is very similar. 

The 3d band of the Mn ion is exactly half-filled with five electrons among the 10 available states, with a gap between the upspin ( ) occupied states and empty downspin (J,) states. For other transition metals, such as Fe, Co, and Ni, one of the bands is usually partially filled (up or down), as shown in Figure 5.2. Table 5.1 shows the oxidation and charge states for some of the transition metals in ZnO and GaN [29]. 

Several patents dealing with the use of volatile metal amidinate complexes in MOCVD or ALD processes have appeared in the literature.The use of volatile amidinato complexes of Al, Ga, and In in the chemical vapor deposition of the respective nitrides has been reported. For example, [PhC(NPh)2]2GaMe was prepared in 68% yield from GaMes and N,N -diphenylbenzamidine in toluene. Various samples of this and related complexes could be heated to 600 °C in N2 to give GaN. A series of homoleptic metal amidinates of the general type [MIRCfNROilnl (R = Me, Bu R = Pr, BuO has been prepared for the transition metals Ti, V, Mn, Fe, Co, Ni, Cu, Ag, and La. The types of products are summarized in Scheme 226. The new compounds were found to have properties well-suited for use as precursors for atomic layer deposition (ALD) of thin films. 

In addition to the shallow donor, three transition metals have been observed in thick GaN layers. Maier and co-workers [10] were able to detect and identify Fe3+, in part by comparison of the fine structure interaction with that of Fe3+ in ZnO. Baranov and co-workers [11,12] have identified Mn2+ by the... 

There are a number of IR bands in GaN either due to transition metal impurities or damage centres. Again, the donor and/or acceptor resonances are often observed on these bands in addition to several IR-specific resonances The first work in this spectral regime involved the Fe3+ luminescence at 1.3 eV by Maier, Kunzer and co-workers [10,22], They studied both MOCVD grown layers (-1 pm thick) and one 40 pm thick Fe-doped VPE sample, which, as mentioned above, was also examined by EPR. The resonance spectra is a 5-line structure due to an S = 5/2 centre as would be expected for Fe3+. They noted that the axial fine structure constant was about 20% larger in the VPE layer (D = -707 x 10"4 cm 1) than in the thin fihns, which they attributed to residual lattice strain in the thin films. There is also a PL line at 1.047 eV which, based on their EPR measurements, Baranov and co-workers [12] have associated with Ni3+. 

FIGURE 1 Near-infrared transition metal PL in GaN samples grown (a) on p-SiC substrate by the sublimation sandwich technique, and (b) on sapphire substrate bv HVPE. 

TABLE 1 Comparison of transition metal photoluminescence in AIN and GaN (see also [16]). 

We have developed solvothermal synthesis as an important method in research of metastable structures. In the benzene-thermal synthesis of nanocrystalline GaN at 280°C through the metathesis reaction of GaClj and U3N, the ultrahigh pressure rocksalt type GaN metastable phase, which was previously prepared at 37 GPa, was obtained at ambient condition [5]. Diamond crystallites were prepared from catalytic reduction of CCI4 by metallic sodium in an autoclave at 700°C (Fig.l) [6]. In our recent studies, diamond was also prepared via the solvothermal process. In the solvothermal catalytic metathesis reaction of carbides of transition metals and CX4 (X = F, Cl, Br) at 600-700°C, Raman spectrum of the prepared sample shows a sharp peak at 1330 cm" (Fig. 1), indicating existence of diamond. In another process, multiwalled carbon nanotubes were synthesized at 350°C by the solvothermal catalytic reaction of CgCle with metallic potassium (Fig. 2) [7]. 

Gans P (1965) The bonding of nitric oxide in transition-metal nitrosyl complexes. Chem Commun (London) 144—145... 

Gans P, Sabatini A, Sacconi L (1966) Infrared spectra and bonding in transition metal nitrosyl complexes. Inorg Chem 5 1877-1881... 

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