Enhanced efficiency in GaInP/GaAs tandem solar cells using carbon doped GaAs in tunnel junction

摘要

Carbon doping of GaAs using CBr_4 (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, CBr_4 was supplied during the cool down process and produced almost constant hole concentration of 1 × 10~(20) cm~(-3) regardless of the depth, when CBr_4 flow rate was 9.53 μmol/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 GalnP/GaAs tandem solar cells.