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We review recent progresses on in-situ observation of lattice relaxation of III-V lattice-mismatched system and analyses of defect properties in III-V-N solar cell materials. We found that there were five phases during the InGaAs growth on GaAs substrate. The transition point of the dominant dislocation behavior could be determined precisely. We also found that compositionally step-graded InGaAs/GaAs(001) buffers with overshooting (OS) layers were effective to control the strain of the top layer from tensile to compression. To understand the defect properties that dominate the electrical property of CBE-grown GaAsN films, we characterized deep levels in CBE-grown GaAsN films by DLTS. In this characterization, a well-known electron trap E1 (Ec-0.33eV) center in n-GaAsN and p-GaAsN was confirmed to be non-radiative recombination center by using double-carrier pulse DLTS.

III-V compound multi-junction solar cells have high efficiency potential of more than 50% due to wide photo response, while limiting efficiencies of single-junction solar cells are 31-32%. In order to realize high efficiency III-V compound multi-junction solar cells, understanding and controlling imperfections (defects) are very important. This paper reviews fundamentals of defects and defect management for III-V compound materials, single-junction, multi-junction, space and concentrator solar cells.

The in situ X-ray reciprocal space mapping (in situ RSM) of symmetric diffraction measurements during lattice-mismatched InGaAs/GaAs(001) growth were performed to investigate the strain relaxation mechanisms. The evolution of the residual strain and crystal quality were obtained as a function of InGaAs film thickness. Based on the results, the correlation between the strain relaxation and the dislocations during the film growth were evaluated. As a result, film thickness ranges with different relaxation mechanisms were classified, and dominant dislocation behavior in each phase were deduced. From the data obtained in in situ measurements, the quantitative strain relaxation models were proposed based on a dislocation kinetic model developed by Dodson and Tsao. Good agreement between the in situ data and the model ensured the validity of the dominant dislocation behavior deduced from the present study.

The amount of residual carbon in the GaAsN film deposited by chemical beam epitaxy (CBE) is decreased by the flow rate modulation growth method (FM-CBE). The number of carbon atoms remained in the grown film increases as the growth temperature decreases. At low temperatures below 440°C, the carbon atoms are mainly originated from the nitrogen source gas mono-methylhydrazine. However, increasing the substrate temperature during the growth causes the deterioration of film qualities and the high growth temperature is not the solution for reducing the impurities. On the other hand, by intermitting the supply of gallium source triethylgallium while the arsenic and nitrogen sources are continuously supplied, the carbon concentration drastically decreases as compared with that grown by the conventional CBE growth. The results of temperature programmed desorption and ab initio calculations suggest that the desorption of adsorbates that contain C atom, such as, NHCH3, is enhanced by the FM-CBE growth, resulting in the decrease of the residual C concentration.

Physical properties of multiple-energy B-ion implanted C60 thin films were investigated for various doses. Fourier Transform Infra-red Spectroscopy (FTIR) results indicate the structural transformation of C60 to amorphous carbon phase during implantation. The conductivity type of the implanted films is found to be p-type and the conductivity measurements reveal a dramatic increase in the conductivity with ion implantation. Temperature dependent conductivity shows the semiconducting nature of the B-ion implanted films. The optical absorption coefficient and optical gap of the implanted films have been observed as a function of B-ion dose. Measurements on implanted films subjected to thermal annealing indicate the removal of the defects caused during the implantation. Ion implantation-induced defects are found to partially annihilate with the annealing temperature. Electrical conductivity and optical gap are determined in the post-implanted films. The observation of the systematic increase in the conductivity of the annealed films is due to the removal of the defects and the formation of defect free boron impurity acceptor.

The important intermediates in the Ti plasma-enhanced CVD using TiCl4/Ar/H2 are investigated by ab initio molecular orbital (MO) calculations. From the experimental point of view, it is pointed out that'TiCls is a key species for the Ti deposition reaction. So, its reactivity with the Si and SiO2 substrates is estimated theoretically from the stabilization energy. The difference of the stabilization energies of TiCl3 between them, which is 12.3kcal/mol in Hartree-Fock level calculations with using the on-top deposition reaction model, indicates a longer existing time by the factor of 102 on SiO2 than on Si. In addition to these calculations, the stabilization energies on the suicide substrates are also calculated and compared with the results on the Si and Si02 substrates. But other reaction paths may have to be considered because the growth rates of Ti thin films onto between Si and SiO2 don't necessarily coincide with the tendency of calculated results.

Copper films are etched at a low temperature of 60 °C using a Cl2 plasma etching method with IR light irradiation. The etch rate is as high as 1 μm/min. The anisotropic Cu line patterns are obtained independent of the Cl2 gas flow rate and the etching pressure conditions. Moreover, there is no corrosion on the etched sample.

Role of in-situ heavy As doping in Si selective growth is studied using the SiH2Cl2/H2/HCl/AsH3 gas system. By increasing AsH3 flow rate, the growth rate decreases in proportion to In (AsH3 flow rate). This result is explained well using a Frumkin-Temkin adsorption model. The As concentrations in grown films depend on surface orientation. Moreover, the maximum As concentration is about ten times lower than the solubility limit at a given temperature. These results are able to be explained qualitatively, if equilibrium concentrations of impurities at the Si(100), the Si(111), and the bulk are assumed to be different from one another, and that the concentration at the surface is frozen in the grown film.

β -SiC is grown on a Si(100) substrate by chemical vapor deposition method under reduced pressure using SiH2 Cl2/C3H8/HCl/H2 gas system. The addition of HCI to SiH2 Cl2/C3H8/HCl/H2 gas system makes it possible to obtain a stoichiometric β -SiC film with a mirror surface at low growth temperature of 900°C. Moreover, β -SiC selective growth on Si(100) surface, with no nucleation on SiO2 surface, is achieved. According to the increase of the HCI flow rate, the density of SiC nucleation on SiO2 surface is greatly decreased. Perfect selective β -SiC film is obtained for HCI concentrations greater than 1.2%.

Silicon vapor phase epitaxial growth with SiH2Cl2 is theoretically studied. The optimized geometries and total energigs of the species, generated from SiH2Cl2, are calculated by using ab initio molecular orbital method. As the intgraction between silicon surface and SiCl2 the charge transfer is considered. Based on the computational result that SiCl2 - has the lower total energy than SiCl2, a new adsorption mechanism, named, charge transfer adsorption, is p~oposed. By using this charge transfer adsorption followed by the surface reaction at the hollow bridge site, the epitaxial growths on the silicon (001), (111), and (110) surfaces are discussed.