InxGa1-xAs/InyGa1-yP Multiple Quantum Wells for Multijunction Solar Cells

In this work, we report results on the growth and characterization of In _x Ga _1-x As/In _y Ga _1-y P multiple quantum wells on GaAs substrates to be used in a triple junction solar cell for spatial applications. The stack of several periods of quantum wells and barriers are intended to compose the active region of the intermediate junction of such device. The structure parameters, such as the layers' thicknesses and alloy contents should be defined to provide an effective bandgap energy, which matches the optimum value of 1.18 eV. Moreover, such parameters are correlated by the condition of strain compensation in order to avoid defect formation due to the large difference in lattice parameters. For this specific material to match the above mentioned requirements, x =0.27 and y =0.25, which are substantially different from the lattice matched values of x = 0 and y =0.48, are needed, according to theoretical simulations. The systematic characterization by x-ray, photoluminescence and reflectance spectroscopies of various MQW structures with increasing x and decreasing y values allowed us to successfully reach x and y equal to 0.16 and 0.35, respectively, demonstrating that our reported approach to reach the ideal alloys' composition using the strain balance technique has great potential.