The design, growth by metal-organic chemical vapor deposition, and processing of an Ino,07G~~93As0~98N0~02 solar cell, with 1 .O eV bandgap, lattice matched to GaAs is described. The hole diffusion length in annealed, n-type InGaAsN is 0.6-0.8 p, and solar cell internal quantum efficiencies > 70% are obtained. Optical studies indicate that defects or impurities, from InGaAsN doping and nitrogen incorporation, limit solar cell performance.Multi-junction tandem solar cells are being developed as power sources for satellite systems operating in air mass zero (AMO) solar radiation. Models indicate that record efficiencies (= 38%) would be obtained for tandem cells where a 1.0 eV bandgap cell is added in series to proven InGaP-GaAs tandem structures.' The In,Ga,~,As,.,N, alloy system appears ideal for this application. Bandgaps of 5 1.0 eV are obtained for In,Ga,~,As,.,N, with minimal N concentrations ( y > 0.02), and the quaternary is latticematched to GaAs for compositions with x = 3y. '' Even at these low concenuations, N incorporation has proven problematic, and it remains a challenge to demonsuate thick (2-3 pm), high quality, In,Ga,.,As,.,N, (y > 0.02) epilayers needed for solar cell development. In this paper, we present a status report on In,Ga,~,As,.,N, properties, growth, and solar cell performance. , Under specialized conditions, we demonstate internal quantum efficiencies >70 9 ' 0 for I . O eV bandgap solar cells.The structures in this work were grown in a vertical flow, high speed rotaling disk, Emcore GS/3200 metalorganic chemical vapor deposition (MOCVD) reactor.In,Ga,-,As,,N, films were grown using trimethylindium (TMIn). lriniethylgallium (TMG), 100% arsine and dimethylhydrazine (DMf-Iy). Dirnetfiylhydrazine wits used x the nitrogen source since it has a lower disassociation temperature than ammonia and has a vapor pressurc or approximately 1 10 torr at 18°C. A significant increase in photoluminescence intensity was observed from these films following a post-growth anneaL4 Ex-situ, post -growth anneals were carried out in a rapid thermal anneal system under nitrogen using a sacrificial GaAs wafer in close proximity to the InGaAsN sample. The photoluminescence intensity was a maximum for samples annealed for either 700OC for 2 minutes or 65OOC for 30 minutes. Secondary ion mass spectrometry measurements showed the residual carbon concentration of similar films to be 6 -8~1 0 '~ cm". Carbon is incorporated during growth at sufficiently high levels to possibly cause the background p-type conductivity and the observed ex-situ annealing behavior.The optical properties of the InGaAsN films were extremely sensitive to N content, ex-situ annealing, and doping. Photoluminescence and optical absorption