Carbon Nanotube - Silicon Heterojunction Hyperspectral Photocurrent Response
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0963-Q22-01
Carbon Nanotube - Silicon Heterojunction Hyperspectral Photocurrent Response Teng-Fang Kuo1, Daniel A. Straus1, Marian Tzolov2, and Jimmy Xu1 1 Division of Engineering, Brown University, Providence, RI, 02912 2 Department of Geology and Physics, Lock Haven University of Pennsylvania, Lock Haven, PA, 17745-9988
ABSTRACT Carbon nanotubes (CNT) have been studied intensively for explorations of their unique electrical and mechanic properties in many applications. However, direct and functional integration of carbon nanotubes with silicon to form an electronically functional structure or device has remained a great challenge. Whereas vertically aligned bundles of nanotubes have been grown previously on silicon, the integration is mechanical, rather than electronical, in nature and the application of such mechanical integration is rather limited. In this work, we report on electronically functional integration of carbon nanotube with silicon, i.e., the formation of an electronic heterojunction by controlled growth of vertical and highly ordered array of ícarbon nanotube - siliconí (CNTS) heterojunctions of uniform diameter, length, and alignment. Moreover, we examine it as a hyperspectral photodiode. From the measured spectral dependence of the photocurrent, one may also extract the band gap of the nanotubes, which we find to be in agreement with that determined from conductance measurements. Mechanism of the infrared photocurrent response is elucidated by the current-voltage (I-V) and radiation intensityphotoresponse measurements. The linear intensity dependence of the photoresponse in the absorption ranges of Silicon and CNTs and the measured I-V characteristics all suggest that the photocurrent responses corresponding to the Silicon and CNT bands both originate from the intrinsic functionality of the heterojunction.
INTRODUCTION Carbon nanotubes (CNT) have been studied intensively since their discovery due to their unique electrical[1-6] and mechanic properties, which are being pursued for applications in field emission displays, bio-sensors, molecular scale electronic device. Moreover, the semiconducting CNTs are direct bandgap materials with very similar effective masses for holes and electrons; this makes them very attractive for optical detection applications. Indeed, first principle considerations suggest that a nanotube-based optical detector could be advantageous in several aspects - scalability of detection wavelength range, potential high performance, and mechanical durability[7]. The inverse relationship between nanotube diameter and bandgap is of primary benefit, and it arises from local coupling between the electronic degree of freedom and the mechanic one. As such, it is present even in imperfect, amorphously graphitic nanotubes[8]. Since nanotubes can be made to have any diameter within a continuous range, their bandgaps and hence the wavelength range can be chosen within a proportionately large continuous spectral range, from a few meV to 1 or even 2 eV. Of special interest are the optical
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