Light-emitting device

A light-emitting device, comprising:

• a first multi-quantum well structure comprising a plurality of first well layers and a first barrier layer stacked alternately, wherein the energy gap of the first barrier layer is larger than that of any one of the first well layers;
• a second multi-quantum well structure comprising a plurality of second well layers and a second barrier layer stacked alternately, wherein the energy gap of the second barrier layer is larger than that of any one of the second well layers;
• a third barrier layer disposed between the first multi-quantum well structure and the second multi-quantum well structure, and the third barrier layer connected with the first well layer and the second well layer, wherein the energy gap of the third barrier layer is larger than that of any one of the first well layers and the second well layers, and the thickness of the third barrier layer is larger than that of any one of the first barrier layer and the second barrier layer;
• a first semiconductor layer having a first conductivity type under the first multi-quantum well structure;
• and
• a set of first structures disposed between the first semiconductor layer and the first multi-quantum well structure, wherein the set of first structures comprises a third well layer and an un-doped or unintentionally-doped fourth barrier layer, and the energy gap of the third well layer is larger than any one of those of the first well layers and the second well layers.