Four tunnel junction (TJ) designs for multijunction (MJ) solar cells under high concentration are studied to determine the peak tunnelling current and resistance change as a function of the doping concentration. These four TJ designs are: AlGaAs/AlGaAs, GaAs/GaAs, AlGaAs/InGaP and AlGaAs/GaAs. Time‐dependent and time‐average methods are used to experimentally characterize the entire current–voltage profile of TJ mesa structures. Experimentally calibrated numerical models are used to determine the minimum doping concentration required for each TJ design to operate within a MJ solar cell up to 2000‐suns concentration. The AlGaAs/GaAs TJ design is found to require the least doping concentration to reach a resistance of <10−4 Ω cm2 followed by the GaAs/GaAs TJ and finally the AlGaAs/AlGaAs TJ. The AlGaAs/InGaP TJ is only able to obtain resistances of ≥5 × 10−4 Ω cm2 within the range of doping concentrations studied. Copyright © 2010 John Wiley & Sons, Ltd.

Low-energy ͑18 keV͒ phosphorus ion implantation and rapid thermal annealing at 650°C for 120 s were used to create point defects and promote intermixing in InAs/ InP quantum stick structures grown by molecular beam epitaxy. With these soft conditions for ion-implantation-induced intermixing, photoluminescence measurements at low temperature show a very large blueshift up to 350 nm and a narrow emission linewidth ͑down to 30 nm for ion dose equal to 5 ϫ 10 13 cm −2 ͒. The band gap tuning limit in this system was evaluated using implantation of phosphorus ions at various doses ͑1 ϫ 10 11-5 ϫ 10 14 cm −2 ͒, at a temperature of 200°C followed by rapid thermal annealing.

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