III-V semiconductors, GaAs and in particular InGaP, are used in many different electronic applications, such as high power and high frequency devices, laser diodes and high brightness LED. Their direct bandgap and high reliability make them ideal candidates for the realisation of high efficiency solar cells: in the past years they have been successfully used as power sources for satellites in space, where they are able to produce electricity from sunlight with an overall efficiency of around 30%. Nowadays, the use of arsenides and phosphides as photovoltaic (PV) devices is confined only to space applications since their price is much higher than conventional Si flat panel modules, the leading PV market technology. But with the introduction of multijunction solar cells capable of operating in high concentration solar light, the area and, therefore, the cost of these cells can be reduced and will eventually find an application and market also on Earth. This article will review the situation of semiconductor solar cell materials, focusing on Si, GaAs, InGaP and multijunction solar cells and will discuss future trends and possibilities of bringing III-V technology from space to Earth

A Raman spectroscopy study on highly mismatched GaAs layers with thickness ranging from 15 nm to 6.6 μm and grown by metal-organic vapor-phase epitaxy on InP (001) substrates, is reported. Both LO and TO GaAs phonons have been observed in backscattering and Brewster geometries. In the thinnest samples large frequency red shifts with respect to the bulk are measured indicating large residual tensile strains. The Raman measurements agree with x-ray-diffraction measurements and confirm that layers thinner than 30 nm exhibit a 3D growth mechanism as suggested by transmission electron microscopy investigations.

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The chemically sensitive (200) diffraction in the dark field (DF) mode of transmission electron microscopy has been used to detect, identify, and evaluate the composition of the parasitic interlayer at the GaAs-on-InGaP interface in metallorganic vapor-phase epitaxy (MOVPE) normalInxnormalGa1−xP∕GaAs heterostructures. The latter were grown at 600°C with no growth interruption. The composition range determined by (200) DF was further refined by using the X-ray diffraction result that the interlayer has a negative lattice mismatch to GaAs. The parasitic interlayer can be either GanormalAs0.45normalP0.55 or normalInxnormalGa1−xnormalAs1−ynormalPy with 0⩽x<0.069 and 0.55⩽y<0.707 . P∕As intermixing and In segregation are assumed to drive the formation of the interlayer. The low In content in the quaternary is ascribed to the reduced In segregation at 600°C . In segregation is likely favored by the tensile strain associated with the interlayer in its process of growth.

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