Abstract
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/C60/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 C60 layer (11 nm) device, which implies competition of the photogenerated carriers between graphene/C60 and C60/pentacene. Meanwhile, we observe a complete positive-negative alternating process under continuous 405 nm irradiation. Furthermore, infrared light modulation of a thin C60 (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 C60 devices. In addition, the tuneable bandwidth of the infrared response from 10 to 3 × 103 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.
Highlights
Graphene has promising potential in fabricating phototransistors and photodetectors owing to its unique band structure with prominent optoelectronic and charge transport properties[1,2,3]
We demonstrate a light modulation method to adjust the response magnitude, speed, and direction of photocurrents based on graphene/C60/pentacene phototransistors with different thickness C60
The bilayer heterojunction C60/pentacene acts as the main light-absorbing layer, which allows photogenerated free carriers to be injected into graphene, modulating the conductance of the channel
Summary
Graphene has promising potential in fabricating phototransistors and photodetectors owing to its unique band structure with prominent optoelectronic and charge transport properties[1,2,3]. The inferior light absorption of single atomic layer graphene limits the phototransistor performance. Some typical 2D localized field methods incorporating 2D, organic, perovskite, and Dirac materials were subsequently proposed to realize high-performance phototransistors[23,24,27,28,29,30,31,32,33]. Numerous localized field-enhanced phototransistors have been integrated with an electrostatic field to achieve distinct features such as a floating-gate structure[27,28], a builtin field[19], a photogating electric field[23,24,29,30] and a ferroelectric field[31]. The ferroelectric field aims to suppress the dark current, and the floating gate aims to promote the light sensitivity
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