Growth and evaluation of lpe graded composition AlxGa1−xAs layers for high efficiency graded bandgap solar cells

A melt-mixing LPE growth technique to obtain a graded composition Al_xGa_1−xAs layer is described. The graded bandgap AlGaAs/GaAs solar cell requires the Al fraction (x) in the Al_xGa_1−xAs surface layer to increase from the junction towards the surface. The graded composition Al_xGa_1−xAs layer creates a built-in electric field for minority carriers which improves the carrier collection process. This graded bandgap solar cell should enable one to realize the full potential of GaAs as a material for solar energy conversion. Quantitative evaluation of the composition profile for these graded layers is needed to develop the proper growth technique and to understand the resulting solar cell characteristics. Rutherford backscattering analysis technique is described which has been successfully used to profile such layers.