Towards Fast Multicolor Photodetectors based on Graphene Contacted   Vertical p-GaSe/n-InSe van der Waals Heterostructure
  We investigated the electronic and optoelectronic properties of vertical van der Waals heterostructure photodetectors using layered p type GaSe and n type InSe, with graphene as the transparent electrodes. Not only the photocurrent peaks from the layered GaSe and InSe themselves were observed, also the interlayer optical transition peak was observed, which is consistent with the first-principles calculation. The built-in electric field between p-n heterojunction and the advantage of the graphene electrodes can effectively separate the photo-induced electron-hole pairs, and thus lead to the response time down to 160 {\mu}s. Making use of the interlayer as well as intralayer optical transitions of the vertical layered p-n heterostructure and graphene electrodes, we could achieve high performance multi-color photodetectors based on two-dimensional layered materials, which will be important for future optoelectronics. 
Faguang Yan, Dong Zhang, Wengang Luo, PingAn Hu, Qi Feng, Chao Shen,   Xia Wei, Kai Chang and Kaiyou Wang
cond-mat.mes-hall cond-mat.mtrl-sci