heterojunction*

The graphene like surface state of topological insulators (TIs) have been attracted plenty of attentions. However, ultra-low saturation absorption resulting from the intrinsic bulk state of TIs limts its application, such as pulse laser. In this work, thickness dependent optical nonlinearity of graphene/Bi₂Te₃ heterojunction saturable absorber is investigated. Unlike the low saturation intensity of Bi₂Te₃ (with order of tens W/cm²), the saturation intensity of graphene/Bi₂Te₃ heterojunction increases dramitically at least 4 order of magnitude. In addition, the increasing modulation depth of around 60% is characterized and the high quality 1um Q-switched solid state laser based on graphene/Bi₂Te₃ heterojunction saturable absorber is accordingly performed. Finally, the possible mechanism of carrier dynamics between p-n heterojunction and guideline for material design are proposed and discussed as well.