Abstract
The photoresponse mechanism of graphene/InSb heterojunction middle-wavelength infrared (MWIR) photodetectors was investigated. The devices comprised a graphene/InSb heterojunction as a carrier-injection region and an insulator region of graphene on tetraethyl orthosilicate (TEOS) for photogating. The MWIR photoresponse was significantly amplified with an increase in the graphene/TEOS cross-sectional area by covering the entire detector with graphene. The graphene-channel dependence of the MWIR photoresponse indicated that the graphene carrier density was modulated by photocarrier accumulation at the TEOS/InSb boundary, resulting in photogating. The dark current of the devices was suppressed by a decrease in the graphene/InSb carrier-injection region and the formation of the heterojunction using an n-type InSb substrate. The results indicate that photocarrier transportation was dominated by the formation of a Schottky barrier at the interface of the graphene/InSb heterojunction and a Fermi-level shift under bias application. The high-responsivity and low-dark-current photoresponse mechanism was attributed to the graphene/InSb heterojunction diode behavior and the photogating effect. The devices combining the aforementioned features had a noise equivalent power of 0.43 pW / Hz1/2. The results obtained in our study will contribute to the development of high-performance graphene-based IR image sensors.
Highlights
Graphene-based infrared (IR) photodetectors are promising devices that take advantage of the unique optoelectronic properties of graphene such as broadband light absorption,[1,2,3] high carrier mobility,[4] high thermal conductivity,[5,6,7] gate-tunable plasmons,[8,9] and strong nonlinear optical response,[10,11,12] as well as its excellent chemical stability
Photoelectrons excited in the InSb under the graphene/tetraethyl orthosilicate (TEOS) contact region accumulate at the TEOS/InSb interface owing
The remaining TEOS region can provide additional photogating by the photocarriers generated in the TEOS/InSb depletion layer, it may be less effective for photoresponse enhancement because the carrier diffusion distance of the InSb is short, at around a few micrometers,[41] and the effective photocarrier region is situated only in the vicinity of the graphene/TEOS region
Summary
Graphene-based infrared (IR) photodetectors are promising devices that take advantage of the unique optoelectronic properties of graphene such as broadband light absorption,[1,2,3] high carrier mobility,[4] high thermal conductivity,[5,6,7] gate-tunable plasmons,[8,9] and strong nonlinear optical response,[10,11,12] as well as its excellent chemical stability. We have proved the graphene/insulator layer region underwent photogating,[3,17,39,40,41,42,43,44] which is one of the most effective responsivity enhancement candidates among possible techniques, such as pn junctions;[45] turbostacking of graphene;[40] plasmonic metamaterial absorbers;[46,47,48] the addition of photosensitizers including MoS2,49,50 ZnO,[51,52] organic semiconductor,[53] and quantum dots;[54,55,56,57] and optical waveguides.[58] Photogating modulates the surface carrier density of graphene by locating a photosensitizer in the vicinity of the graphene This multiplies the photocarrier transport from the graphene/semiconductor heterojunction region. The MWIR photoresponse performance of the devices that combined the features above was evaluated
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