We have investigated the lattice site location of B in Si using ion channeling in combination with nuclear reaction analysis (NRA). Silicon samples implanted with Boron at an energy of 10 keV and a dose of 5 × 1014 cm−2 (low dose samples) or 5 × 1015 cm−2 (high dose samples) were annealed at 1000 °C for 10 seconds (RTA) or at 800 °C for 10 minutes (FA). The activation efficiencies of these samples were estimated from the B atomic concentration and the hole concentration obtained by secondary ion mass spectrometry (SIMS) and spreading resistance profiling (SRP), respectively. We also studied the ion implantation damage of Si crystals using ion channeling combined with Rutherford backscattering spectrometry (RBS). We found that the activation efficiency is proportional to the substitutionality, meaning that substitutional B is fully activated without any carrier compensation. We also found that B atoms go to the substitutional sites and are activated up to the solubility limit in the high dose samples. However, the ion implantation damage of the crystalline Si in the high dose samples increases somewhat after annealing.
We report a GaAs tunnel junction grown by all-solid-state molecular beam epitaxy (MBE), using tellurium (Te) and magnesium (Mg) as n- and p-type dopants, respectively. The growth conditions, including V/III ratio, and growth rate, growth temperature, were optimized. Through these optimizations, Te- and Mg-doped GaAs with high carrier concentrations as well as good mobilities were obtained. A GaAs tunnel junction with a peak current density of 21 A/cm2 was demonstrated.
We have developed III-V compound semiconductor multi-junction solar cells by a room-temperature wafer-bonding technique to avoid the formation of dislocations and voids due to lattice mismatch and thermal damage during a conventional high-temperature wafer-bonding process. First, we separately grew an (Al)GaAs top cell on a GaAs substrate and an InGaAs bottom cell on an InP substrate by metal solid source molecular beam epitaxy. Thereafter, we successfully bonded these sub-cells by the room-temperature wafer-bonding technique and fabricated (Al)GaAs k InGaAs wafer-bonded solar cells. To the best of our knowledge, the obtained GaAs k InGaAs and AlGaAs k InGaAs wafer-bonded solar cells exhibited the lowest electrical and optical losses ever reported. The AlGaAs k InGaAs solar cells reached the maximum efficiency of 27.7% at 120 suns. These results suggest that the room-temperature wafer-bonding technique has high potential for achieving higher conversion efficiencies.
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