**6. Conclusion**

Dilute nitride GaAsN and InGaAsN epitaxial layers have been prepared by lowtemperature LPE using polycrystalline GaN as a source for nitrogen. The GaAsN layers, 0.8- 1.5 μm thick, with 0.15-0.6 at. % N content in the solid have been grown from different initial epitaxy temperature varied in the range 650-550 °C. The lowering the epitaxy temperatures favors nitrogen incorporation in the layers. The Hall measurements reveal sharply increase of free carrier concentrations about one order of magnitude and decrease of Hall mobility for GaAsN samples in comparison with undoped GaAs.

Lattice-matched conditions for coherent growth of InGaAsN layers on GaAs have been found. The results suggest preferential In-N bond formation for high quality growth of these alloys. Temperature dependent electronic transport measurements show a thermally activated increase in the free carrier concentration at measurement temperatures higher than 200 K, suggesting the presence of carrier trapping levels below the GaAsN conduction band edge. Nearly lattice matched to GaAs substrate thick InxGa1-xAs1-yNy (x~ 6.4%, y~2.8%) layers exhibit high values over 2000 cm2/ V.s for Hall electron mobility.

Further study is necessary in order to determine the potential of melt-grown quaternary InGaAsN alloys for solar cell application. This will be attained by: study the influence of growth conditions on the material quality in wide temperature range 450-600 °C and differentiation between intrinsic and extrinsic limitations for device performance; finding optimized growth conditions for InGaAsN lattice matched to GaAs with improved material quality ; extending the long-wavelength limit of GaAsN-based materials by the lowering the band gap energy of dilute nitride structure that can be lattice matched grown on GaAs.

The finale goal is a development of single-junction solar cells with high photovoltaic parameters.
