Low-Acceptor-Concentration GaInNAs Grown by Molecular-Beam Epitaxy for High-Current p-i-n Solar Cell Applications

We report GaInNAs grown by solid-source molecular-beam epitaxy (MBE) with background acceptor concentrations less than 1014 cm-3, yielding depletion widths in excess of 3 μm. GaInNAs p-i-n solar cells fabricated from this low-acceptor-concentration material show greatly increased photocurrents and internal quantum efficiencies close to unity for band gaps as low as 1.15 eV. The low acceptor concentrations may be due to low levels of background impurities, such as hydrogen and carbon, in the MBE-grown layers. We discuss the dependence of the acceptor concentration on the substrate temperature used for GaInNAs growth.