Double GaAs/Si Heterojunction Layers in Si Solar Cells Fabricated by Electron Beam Evaporation

We investigated silicon solar cells with double gallium arsenide heterojunctions. Both p-type and n-type GaAs were deposited on the back and front side of the Si pn junction using an electron beam evaporator under a high vacuum condition to fabricate ppnn cells, respectively. The ppnn cell with a micro-textured Si surface showed enhanced quantum efficiency by about 10% in the shorter wavelength region and by about 1% in the longer wavelength region compared to ppnn cell with nanotextured Si surface. Moreover, the average minority carrier lifetime was increased by 1 mu s and conversion efficiency was increased by 0.74% for the micro-ppnn cell despite its high series resistance. Morphological analysis showed that GaAs thin-film on Si surface was As-rich in the as-deposition case. It became distorted at higher annealing temperatures, leading to formation of cracks. Moreover, annealing of the deposited GaAs on a nano-textured Si surface at 100 degrees C for 30 min resulted in formation of GaAs nanodots in an amorphous GaAs matrix.