Enhanced efficiency in GaInP/GaAs tandem solar cells using carbon doped GaAs in tunnel junction
Carbon doping of GaAs using CBr4 (carbon tetrabromide) in metal-organic chemical vapor deposition (MOCVD) was investigated to obtain very high and sharp doping profiles required for tunnel junction in tandem solar cells. It was found that the hole concentration increased with decreasing growth temperature and V/III ratio. Hole doping profiles versus distance from the sample surface showed that the hole concentration near the surface was very low in comparison with that far below the surface. As a post-growth treatment, CBr4 was supplied during the cool down process and produced almost constant hole concentration of 11020cm?3 regardless of the depth, when CBr4 flow rate was 9.53?mol/min. Based on these results, solar cells were fabricated using both carbon (C) and zinc (Zn) as a p-type dopant. It was shown that C doping exhibits higher efficiency and lower series resistance than those of Zn doping in GaInP/GaAs tandem solar cells.
gaas tandem solar cells carbon doping mocvd