Growth and characterization of high efficiency GaAIAs/GaAs/Ge solar cells

The nucleation stage of the GaAs/Ge growth has been investigated in the growth rate range 2-20 mu m/h. Nearly perfect surface morphology can be obtained on sample thicker than the critical thickness for the generation of misfit dislocation for deposition rate of 16 mu m/h. It is shown that V-shaped defects, typically found on GaAs/Ge LP-MOVPE grown heterostructures can be eliminated by selecting low V/III ratio. The growth rate of solar cell buffer layer is found to play an important role for increasing the open circuit voltage (Voc) of the device: Voc as high as 1079 mV are reported for AlGaAs/GaAs/Ge solar cell with temperature coefficient of -1.98 mV/degrees C. The presence of the cascade effect related to GaAs/Ge solar cell is disussed and the influence of misfit dislocation density on the open circuit voltage of the device is shown.