Slow and fast light processes,based on both structural and material dispersions,are realized in a wide tuning range in this article.Coherent population oscillations (CPO) in electrically tunable quantum dot semiconductor optical amplifiers lead to a variable group index ranging from the background index (nbgd) to ～ 30.A photonic crystal waveguide is then dispersion engineered and a group index of 260 with the normalized delay-bandwidth product (NDBP) of 0.65 is achieved in the proposed waveguide.Using comprehensive numerical simulations,we show that a considerable enhancement of slow light effect can be achieved by combining both the material and the structural dispersions in the proposed active QDPCW structure.We compare our developed FDTD results with analytical results and show that there is good agreement between the results,which demonstrates that the proposed electrically-tunable slow light idea is obtainable in the QDPCW structure.We achieve a total group index in a wide tuning range from nbgd to ～ 1500 at the operation bandwidth,which shows a significant enhancement compared with the schemes based only on material or structural dispersions.The tuning range and also NDBP of the slow light scheme are much larger than those of the electrically tunable CPO process.