Due　to　the　weak　absorption　and　low　light-matter　interaction　of　MoS2,　intrinsic　MoS2　photodetector　usually　has　low　photoresponse,　thus　limiting　its　real　application.　Herein,　MoS2　homojunction　was　constructed　by　using　the　chemical　vapor　deposition　grown　intrinsic　MoS2　films　and　the　Nb-doped　MoS2　films.　The　results　show　that　the　Nb　doping　will　induce　p-type　doping　in　MoS2,　where　the　electron　concentration　will　decrease　by　2.08　x　10(12)　cm(-2)　after　Nb　doping.　By　investigating　the　photoelectric　effect　of　MoS2/Nb-doped　MoS2　homojunction-based　phototransistor,　the　tunability　of　the　photoresponse,　detectivity　as　the　function　of　the　external　field,　wavelength,　and　power　of　light　have　been　studied　in　detail.　The　results　show　that　the　photoresponse　and　detectivity　are　strongly　dependent　on　the　gate　voltage　due　to　the　external　field　tuned　interlayer　photoexcitation　attributing　to　the　band　bending.　The　maximum　of　photoresponse　can　reach　51.4　A/W,　the　detectivity　can　reach　3.0　x　10(12)　Jones,　which　is　two　orders　higher　than　that　of　intrinsic　MoS2.　Furthermore,　by　correlating　the　photoresponse　and　detectivity　with　the　external　field,　it　is　found　that　the　photodetection　of　MoS2　homojunction　can　be　significantly　tuned　and　exhibit　well　photodetection　in　infrared.　This　comprehensive　work　not　only　sheds　light　on　the　tunable　photoexcitation　mechanism　but　also　offers　a　strategy　to　achieve　a　high-performance　photodetector.　(C)　2022　Published　by　Elsevier　Ltd　on　behalf　of　The　editorial　office　of　Journal　of　Materials　Science　&　Technology.