Light-modulated vertical heterojunction phototransistors with distinct logical photocurrents

The intriguing carrier dynamics in graphene heterojunctions have stimulated great interest in modulating the optoelectronic features to realize high-performance photodetectors.However,for most phototransistors,the photoresponse characteristics are modulated with an electrical gate or a static field.In this paper,we demonstrate a graphene/C_(60)/pentacene vertical phototransistor to tune both the photoresponse time and photocurrent based on light modulation.By exploiting the power-dependent multiple states of the photocurrent,remarkable logical photocurrent switching under infrared light modulation occurs in a thick C_(60) layer(11 nm)device,which implies competition of the photogenerated carriers between graphene/C_(60) and C_(60)/pentacene.Meanwhile,we observe a complete positive-negative alternating process under continuous 405 nm irradiation.Furthermore,infrared light modulation of a thin C_(60)(5 nm)device results in a photoresponsivity improvement from 3425 A/W up to 7673 A/W,and we clearly probe the primary reason for the distinct modulation results between the 5 and 11 nm C_(60) devices.In addition,the tuneable bandwidth of the infrared response from 10 to 3×10^(3) Hz under visible light modulation is explored.Such distinct types of optical modulation phenomena and logical photocurrent inversion characteristics pave the way for future tuneable logical photocurrent switching devices and high-performance phototransistors with vertical graphene heterojunction structures.