High-performance graphene/InSb heterojunction photodetectors for high-resolution mid-infrared image sensors

Abstract

Graphene/semiconductor heterojunction photodetectors have the potential to outperform conventional infrared (IR) sensors. A high-performance graphene/indium antimonide (InSb) heterojunction photodetector for high-resolution mid-IR image sensors was developed using an undoped InSb substrate with low carrier density. The width of the depletion layer at the graphene/InSb interface was increased because of the low carrier density of undoped InSb, which resulted in a low dark current for the proposed device. In addition, the low carrier density resulted in an increased capacitance change due to photocarrier generation for the depletion layer upon light irradiation. As a result, the carrier density modulation effect of graphene was also amplified owing to the photogating effect. Consequently, low dark currents on the order of nanoamperes and high responsivities of over 2 A/W were achieved over a wide voltage range of −0.05 to −0.5 V using our proposed photodetector. The best performance achieved for the developed photodetector corresponded to a specific detectivity (D*) of 2.28 × 1010 cm Hz1/2/W and a noise-equivalent-power of 0.13 pW/Hz1/2, which makes these detectors suitable for use in mid-IR image sensors, realizing a low dark current of just −7.5 nA over the wide wavelength range of 3–5 μm. These results demonstrate that an IR image sensor with detection performance better than those developed using existing graphene-based photodetectors can be obtained by adopting a simple graphene/InSb heterojunction with undoped InSb, owing to the photogating effect.