We report on a technique for optimizing transport properties in p- and n-type AlGaN/GaN and GaN/InGaN superlattices. As we show highly conductive heterostructures can be obtained by inserting a graded doped layer, which reduces the barrier height while maintaining high sheet carrier density. For optimized p-type AlGaN/GaN SL, an eight fold reduction of the barrier height and a 1.5 times increase in sheet hole density is obtained compared to typical SL. The optimized structure yields 13 orders of magnitude improvement in vertical conductivity (σ<sub>V</sub>) compared to typical SL, and 35 times improvement in lateral conductivity (σ<sub>L</sub>) compared to bulk p-GaN. For optimized p-type GaN/InGaN SL, an improvement of more than 10 orders of magnitude in σ<sub>V</sub> compared to typical SL is obtained with σ<sub>L</sub> better than that of bulk p-InGaN. We also investigate n-type SLs as current spreading layers. A significant improvement in current distribution is obtained for the optimized SLs.