SBIR/STTR Award attributes
This proposal seeks to address the need for improved performance in infrared imaging systems by developing an unconventional infrared detector technology. We seek to demonstrate performance improvements based on an emerging class of novel materials, namely bismuth chalcogenides, and a detector architecture employing graphene / bismuth chalcogenide heterointerfaces to facilitate efficient charge transfer. In contrast to many traditional II-VI and III-V semiconductor-based infrared detector materials, bismuth chalcogenides (bismuth telluride, bismuth selenide, and their alloys) exhibit highly complex non-parabolic band structure and have therefore received significant interest in the last decade as topological insulator (TI) materials. A small but compelling body of literature has examined the possibility of combining TI bismuth chalcogenides with another material such as silicon or graphene to form a novel and viable alternative technology for efficient optical detection. TI Surface states have been found to exhibit high absorption coefficients, and they allow for absorption of photons with sub-bandgap energy, resulting in extremely broadband response into and far beyond the MWIR (3-5 micron) and LWIR (8-12 micron) spectral ranges. However, these same TI surface states also permit rapid recombination of photo-generated electron-hole pairs, which decreases detector responsivity. The problem of low responsivity has previously been addressed through the formation of a heterointerface between the TI and another material such as silicon or graphene, where a built-in electric potential separates photo-generated carriers before they recombine. We wish to emphasize that prior work has focused on demonstrating strong photoresponse rather than high signal-to-noise ratio (SNR), which is ultimately required for good detector performance. Indeed, TI-based photodetector results obtained thus far are encouraging in terms of high speed and broadband response, but these detectors usually exhibit low quantum efficiency (QE) due to the necessary use of very thin absorbing layers. TI photodetectors can possess substantial photoconductive gain, which can produce large effective QE and high responsivity, however the intrinsically low QE of thin absorbers is still a fundamental limitation for good SNR. Such a level of performance is clearly insufficient for the applications targeted by this proposal. The goal of this work is to explore the viability of semiconducting, rather than TI, bismuth chalcogenides as MWIR and LWIR absorption materials, while retaining their ability to form efficiently charge-coupled hybrid interfaces with graphene, thus enabling a new type of highly efficient, bismuth chalcogenide-based, charge-transfer-mediated infrared detector.
