Group III nitrides

AlGaAs Heterostmcture lasers, solar cells, field effect transistors (FETs) 

GaSb/AlGaSb Thermal imaging devices, environmental sensors 

However, high-quality GaN growth was achieved by depositing a very thin AIN (from Mc3Al and NH3) or GaN layer at low temperature. 

Further information about the surface chemistry occurring during the MOCVD of AIN was provided by Fourier-transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) studies on mixtures of Mc3Al 

Trimethylsilylazide (MesSiNs) has been utilized as an alternative nitrogen source for the formation of AIN films, when used in combination with MesAl. AIN films were deposited by atmospheric pressure MOGVD at 300-450 °C, and notably no silicon was detected by AES. The proposed mechanism for the formation of AIN from MesSiNs and MesAl involved the formation of [Me2AlN3] 3 in the gas phase with concomitant production of tetramethylsilane 

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Gillis H P, Choutov D A and Martin K P 1996 The dry etching of Group iii-Nitride wide bandgap semiconductors J. Mater. 48 50-5... 

S. F. DenBaars and S. Keller, Metalorganic Chemical Vapor Deposition (MOCVD) of Group III Nitrides... 

A. Trampen, O. Brandt, and K. H. Ploog, Crystal Structure of Group III Nitrides... 

W. R. L. Lambrechl, Band Structure of the Group III Nitrides N. E. Christensen and P. Perlin, Phonons and Phase Transitions in GaN S. Nakamura, Applications of LEDs and LDs /. Akasaki and H. Amano, Lasers... 

The second contribution by A. Devi, R. Schmid, J. Muller and R. A. Fischer entitled Materials Chemistry of Group 13 Nitrides reviews the organometalHc precursor chemistry of group-III nitride OMCVD. The authors discuss the various efforts undertaken in the past decade to come up with alternative precursors to compete with the classical system of Ga(CH3)3 and NH3 to grow GaN, which is commercially employed in industry. The potential of the rather exotic organometallic azide compounds as precursors for the nitride materials is critically discussed, showing the limitations and prospects of that approach as well as representing one of the few examples of comprehensive studies on... 

Neumayer DA, Ekerdt JG (1996) Growth of group III nitrides. A review of precursors and techniques. Chemistry of Materials 8(1), 9-25... 

STRUCTURAL, MECHANICAL AND THERMAL PROPERTIES OF GROUP III NITRIDES... 

A1.1 Common crystal structures of the group III nitrides A1.2 Lattice parameters of the group III nitrides A1.3 Mechanical properties of the group III nitrides A1.4 Thermal properties of the group III nitrides... 

A 1.1 Common crystal structures of the group III nitrides B HETEROEPITAXIAL LAYERS... 

The mechanical properties of materials involve various concepts such as hardness, shear and bulk modulus. The group III nitrides are now mostly used as fihns or layers grown by metal organic vapour phase epitaxy (MOVPE) or molecular beam epitaxy (MBE) on sapphire, GaAs or SiC. The lattice parameters of the substrate do not generally match those of the deposited layer, and therefore, stresses appear at the interface and in the layer and modify its physical properties. Hence, it is necessary to have a good knowledge of these properties. 

From the results presented in this Datareview, the quality of the crystals is clearly one of the main problems for the precise determination of the physical properties of the group III nitrides. This is especially true for indium nitride, where no elastic moduli could be measured, due to the lack of single crystals. The differences between the elastic moduli measured with the same technique (Brillouin scattering) in GaN is further proof that the quality and the nature (bulk single crystals or epitaxial layer) of the samples is of primary importance. 

Nevertheless, some conclusions may be drawn from the set of results presented here. First, with the notable exception of InN, the group III nitrides form a family of hard and incompressible materials. Their elastic moduli and bulk modulus are of the same order of magnitude as those of diamond. In diamond, the elastic constants are [49] Cu = 1076 GPa, Cn = 125 GPa and Cm = 577 GPa, and therefore, B = (Cn + 2Ci2)/3 = 442 GPa. In order to make the comparison with the wurtzite structured compounds, we will use the average compressional modulus as Cp = (Cu + C33)/2 and the average shear modulus as Cs = (Cu + Ci3)/2. The result of this comparison is shown in TABLE 8. 

TABLE 8 Elastic moduli of diamond and group III nitrides (averaged - see text) in GPa. 

In this Datareview, we have reviewed the mechanical properties of the group III nitrides. From this point of view, they form a very homogeneous family of compounds, with large elastic moduli, both compressional and shear, and bulk moduli of the same order of magnitude as that of diamond. 

The specific heat of a semiconductor has contributions from lattice vibrations, free carriers and point and extended defects. For good quality semi-insulating crystals only the lattice contribution is of major significance. Defect-free crystals of group III nitrides are difficult to obtain, and thus the specific heat measurements are affected by the contributions from the free carriers and the defects. While the specific heat of AIN is affected by the contribution of oxygen impurities, the data for GaN and InN are affected by free electrons, especially at very low temperatures. 

The experimentally measured specific heat of metal group III nitrides and the phonon determined specific heat for several chosen Debye temperatures are presented in FIGURE 1. 

For most group III nitride crystals, their perfection is still far from ideal. Therefore, the thermal conductivity is determined by point defects in the case of single crystals and by point defects and grain... 

Thermal expansion of a semiconductor depends on its microstructure, i.e. stoichiometry, presence of extended defects, ffee-carrier concentration. For GaAs [24] it was shown that for samples of free-electron concentrations of about 1019 cm"3, the thermal expansion coefficient (TEC) is bigger by about 10% with respect to the semi-insulating samples. Different microstructures of samples examined in various laboratories result in a large scatter of published data even for such well known semiconductors as GaP or GaAs. For group III nitrides, compounds which have been much less examined, the situation is most probably similar, and therefore the TECs shown below should not be treated as universal values for all kinds of nitride samples. It is especially important for interpretation of thermal strains (see Datareview A 1.2) for heteroepitaxial GaN layers on sapphire and SiC. 

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