Effects of various dopants on properties of GaAs tunneling junctions and p–i–n solar cells

Several GaAs tunneling junctions (TJs) and p–i–n single junction solar cells grown using a planetary metalorganic vapor phase epitaxy (MOVPE) reactor utilizing various dopant species including Zn, C, S, and Te were investigated. The incorporation of Te atoms into GaAs was approximately two orders larger than that of S atoms. Although only 30% of Te atoms could be electrically activated, a carrier concentration of 10 19 cm −3 was achieved. Highly C-doped GaAs was successfully obtained by decreasing the growth temperature and increasing the amount of H 2 carrier gas in order to prevent the predecomposition of CBr 4 dopant gas. A hole concentration of about 10 20 cm −3 was realized with a growth temperature of 450 °C. The C–Te-doped GaAs TJ exhibited the best ohmic tunneling behavior with a resistivity of 12.5 mΩ·cm 2 , while the others had diode characteristics. The GaAs solar cell grown with the Zn–S dopant showed the highest conversion efficiency ascribed to a longer minority carrier lifetime.