A new structure for III-V avalanche photodetectors in which multiplication is dominated by a single-carrier type is proposed. Calculations for a GaAs-AlGaAs detector are reported predicting multiplication dominated by electrons. The reason for this is that electrons are injected into GaAs multiplication layers from high-electric-field AlGaAs layers, while holes are injected into the GaAs layers from low-electric-field AlGaAs layers.