Solar-Blind Ultraviolet Photodetectors Based on Vertical Graphene-Hexagonal Boron Nitride Heterostructures
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MRS Advances © 2020 Materials Research Society DOI: 10.1557/adv.2020.331
Solar-Blind Ultraviolet Photodetectors Based on Vertical Graphene-Hexagonal Boron Nitride Heterostructures Jesse E. Thompson, Darian Smalley, Masahiro Ishigami Department of Physics and Nanoscience Technology Center, University of Central Florida, Orlando, FL 32826, U.S.A.
ABSTRACT
Photodetectors operating in the ultraviolet (UV) play a pivotal role in applications such as ozone monitoring and biosensing. One key factor to successfully implementing such photodetectors is that they must be solar-blind to avoid detecting ambient visible and infrared light. Unfortunately, UV photodetectors based on silicon and other typical semiconductors are not natively solar-blind, since their band gap energies are in the visible range. Hexagonal boron nitride (h-BN) is an example of a wide band gap semiconductor which shows promise for use as the absorbing medium in a UV photodetector device, since its band gap is wide enough to make it inherently insensitive to light in the visible range and above. Here we report on the fabrication and characterization of a graphene-h-BN-heterostructure photodetector which utilizes a vertical geometry, in principle allowing for highly scalable production. We find that our device shows a finite photoresponse to illumination by a 254 nm light source, but not to a 365 nm source, thus suggesting that our device is solar-blind.
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INTRODUCTION The sun delivers light with a broad range of wavelengths from the vacuum ultraviolet (UV) into the far infrared [1]. Ozone molecules in the Earth’s stratosphere absorb light in the range of 200 - 280 nm (the UVC range) [2] while other molecular species in air absorb light with wavelengths shorter than 200 nm. As such, the irradiance from the sun is absent below 280 nm at the surface of the Earth and UVC light, which interacts minimally with air, can be exploited for defense, ozone layer monitoring [3-5], and biosensing applications. This has led to a strong interest in developing compact, low cost solar-blind UV detectors operating at wavelengths between 200 nm and 280 nm [612] for terrestrial applications. Recent studies have shown that thin multilayer hexagonal boron nitride (h-BN) can be used as the photo-active material in UV photoconductive detectors [13-15]. These photoelectric devices demonstrated their sensitivities at the wavelengths between 120 nm - 225 nm, since h-BN is a wide band gap semiconductor with a 5.5 - 5.97 eV band gap energy [16-19]. Enhancing sensitivities of h-BN-based UV detectors at longer wavelengths in the useful UVC range with energies below its electronic band gap remains a challenge. However, h-BN may be materially advantageous compared to other wide band gap semiconductors for solar-blind UV detection. h-BN possesses exce
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