Properties of 'bulk' GaAsSbN/GaAs for multi-junction solar cell application: Reduction of carbon background concentration

GaAsSbN epitaxial films on GaAs substrate grown by metalorganic vapor phase epitaxy (MOVPE) were investigated for integration into multi-junction solar cells. These films are nominally lattice-matched to the GaAs substrate with band gap energies (E_g) in the 1-1.3 eV range. The high background carbon concentrations often observed in MOVPE-grown dilute-nitride materials are correlated with poor minority carrier lifetime and hence low photoluminescence (PL) intensity. In the MOVPE growth of dilute-nitride materials, this background hole concentration is quite sensitive to the selection of the gallium and antimony precursor, and the growth temperature. The lowest background carbon concentration is achieved in the dilute-nitride-antimonide alloys when triethyl gallium (TEGa) and Tris-dimethylamino antimony (TrisSb) sources are utilized. Based on GaAsSb/GaAs superlattice (SL) growth, higher-Sb incorporation efficiency occurs when TEGa and TrisSb are utilized compared to films grown using trimethyl gallium (TMGa) and trimethly antimony (TMSb) precursors. The background hole concentration of GaAsSbN (E_g ∼1.23 eV) grown using TEGa and TrisSb is an order of magnitude lower than that observed when using TMGa and TMSb. Hall measurements indicate a background hole concentration of ∼8.5×10¹⁷ cm^-3 (E_g ∼1.23 eV) from the thermally annealed GaAsSbN films grown at 525 °C using TEGa and TrisSb. In addition, higher growth temperature 610 °C is utilized for further reducing the background hole concentration (3.2×10¹⁷ cm^-3). Carrier lifetimes of up to ∼448 psec were obtained from thermally annealed GaAsSbN double hetero (DH) structure samples with energy bandgap ∼1.25 eV.