N-type　AlGaAs　Bragg　reflectors　(DBRs)　are　an　important　part　of　optoelectronic　devic-type　AlGaAs　Bragg　reflectors　(DBRs)　are　an　important　part　of　optoelectronic　devices　such　as　light-emitting　diodes　and　vertical　cavity　surface　emitting　lasers　and　reducing　the　series　resistance　is　critical　to　the　performance　of　the　device.　In　this　paper,　four　kinds　of　modulation-doped　20-cycle　N-type　Al0.5Ga0.5As/AlAs　DBR　were　grown　on　N-type　GaAs　substrate　by　MOCVD.　The　white　light　reflection　spectrum　measurement　results　show　that　the　peak　wavelength　of　the　epitaxial　wafer　meets　the　requirements　of　red　light　band.　The　upper　and　lower　electrodes　were　prepared　for　each　of　the　four　structures,　and　the　IV　characteristics　were　tested　after　Cleavaged.The　results　show　that　the　series　resistance　of　the　epitaxial　wafer　with　the　AlGaAs　layer　concentration　of　1x10(19)　cm(-3)　and　the　AlAs　layer　doping　concentration　of　5x10(18)　cm(-3)　is　the　smallest.　The　resistance　value　was　1.36x10(-6)　Omega　cm(2).　It　shows　that　the　modulation　doping　method　can　effectively　reduce　the　series　resistance　of　DBR.