Photocurrent of 1 eV GaInNAs Lattice-Matched to GaAs

The spectral photocurrent response, or quantum efficiency, of GaInNAs lattice-matched to GaAs with a bandgap of 1 eV has been measured in an electrochemical cell in order to optimize material quality for use in a multijunction solar cell lattice-matched to GaAs or Ge. GaInNAs with about 3% nitrogen grown by MOVPE using dimethylhydrazine as a nitrogen source was found to be p-type with hole concentrations of about 1 × 10¹⁷ cm^-3, possibly due to unintentional carbon doping as observed by SIMS. This unintentionally doped material typically had up to 20% internal quantum efficiencies and an absorption coefficient of about 10 000 cm^-1, 200 meV above the bandedge. By doping the material with Si, Se, or Zn, we find that the quantum efficiency is strongly correlated with the carrier concentration because the quantum efficiency is limited by the junction depletion width rather than the bulk minority carrier diffusion length. Low minority carrier lifetimes and mobilities both appear to contribute to these short diffusion lengths. We have observed significant increases in temperature dependent Hall mobilities and photoluminescence intensities due to changes in growth conditions and post-growth anneals.