We studied the relationship of the superlattice structure with the doping efficiency in detail by semi-classic calculation and follow experiment. The results show that period length of about 9nm and Al content of 30% is optimal. The Hall, AFM and PL measurement show that the best annealing temperature under atmosphere is about 540°C to 580°C. Finally we obtained the sample with resistivity of 0.31Ω·cm. It can be used for fabricating p type ohmic contact and active layer for blue LED.