In this case the atomic thin profile of the 2D material that constitutes the transistor channel with very high mobility and gate-tunable Fermi level has been instrumental in realizing photodetectors with very high gain and sensitivity comparable to that of single crystalline counterparts. There has been a significant body of published literature on 2D material-based photodetectors, a phenomenon quite typical when a new material platform is discovered.
Yet, in the process of maturing, there has to be a progressive focus towards solutions that are uniquely enabled by this innovative platform, instead of competing with existing technologies. When it comes to photodetectors there is a set of key performance indicators that characterize the potential of a new technology to become disruptive.
One important figure of merit is the sensitivity of the detector, in which three metrics have to be carefully measured under the same experimental conditions, and reported as a function of electrical bandwidth, temperature, and optical wavelength.
Photodiode Theory of Operation
These are the quantum efficiency, the responsivity and the noise current of the detector. The responsivity is the electric current that flows per watt of incident optical power, and can reach very high values in the presence of a photoconductive gain mechanism. Yet, what finally determines the sensitivity of a detector is the combination of its responsivity and noise current.
It is noteworthy that in a significant portion of published literature the latter is calculated at the shot noise limit, a condition that is rarely met in photodetectors, in particular photoconductive detectors. A large body of literature has reported the achievement of ultrahigh gain and consequently record high responsivity values 9 , 12 , Yet the cost that needs to be paid for reaching a high gain is often underestimated: that of the photodetector speed, which is of paramount importance for a large number of applications.
In most of the cases the detector itself should be even faster than that in order to allow for real-time read-out and processing in image sensor arrays.
Gain is proportional to the mobility of the transistor channel and the carrier lifetime, the latter determining the speed of the detector. The origin of very high gain is often due to the very long lifetimes, in some cases on the order of seconds or tens of seconds. Such long lifetimes will likely prevent the photodetector from addressing a real world application, thus efforts towards gain improvement should be focused on increasing carrier mobility rather than prolonging carrier lifetime.
Thus, the ultimate figure of merit to be looked upon is the gain bandwidth product, and not the gain itself. Likewise, in the case of photodiodes or graphene-based p - n junction detectors, the speed of a photodetector is of paramount importance especially in time-of-flight remote sensing or data communications.
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Again, the reports on the speed of the detector have to be documented at relevant conditions, and followed by a full characterization of the detector in achieving high speed without sacrificing other key figures of merit such as the quantum efficiency and the sensitivity. A fast photodetector must also be sensitive enough and operate at realistically relevant conditions in terms of temperature, form factor etc. The possibility offered by the 2D materials to operate high sensitivity detectors not in a photodiode mode but in phototransistors may offer additional advantages in achieving compact highly sensitive infrared detectors and bolometers.
Overview of performance metrics of standard and 2D-based photodetector technologies. The top left region corresponds to high gain-bandwidth-product detectors and should be the ultimate performance target of future 2D-based photodetectors. When it comes to disruptive technologies and their entry into existing markets or opening new markets, besides their competitive aspects in key performance indicators or cost, another equally, if not more important, aspect is their manufacturing readiness levels.
This is particularly relevant in the case of 2D materials, in view of their unique form factor and requirements of not-standardized integration processes, especially in CMOS foundries. There are already a few strong examples of their potential to augment or even replace current photodetector technologies 6 , To this end, a consolidated and convincing roadmap is required to warrant the successful adoption of 2D material-based technologies in production lines.
Significant efforts are still needed to address doping non-uniformities, batch-to-batch variability arising from growth or even transfer variability issues, as well as hysteretic effects that are sometimes present in graphene and 2D materials due to their interaction with their local environment. Solutions to those challenges should also be scalable, and should not introduce additional complexity in manufacturing.
There is indeed a substantial potential for 2D materials to play a crucial role in the next generation of photodetectors, image sensors, optical transceivers, spectrometers etc. Whether this becomes a reality will depend largely on the successful rise of those initial demonstrators both in technology- and manufacturing- readiness levels through synergism of researchers with semiconductor foundries and key industrial players. Koppens, F. Photodetectors based on graphene, other two-dimensional materials and hybrid systems.
Xia, F. Ultrafast graphene photodetector.
Mueller, T. Graphene photodetectors for high-speed optical communications. Pospischil, A. CMOS-compatible graphene photodetector covering all optical communication bands. Liu, C. Graphene photodetectors with ultra-broadband and high responsivity at room temperature.
Massicotte, M. Picosecond photoresponse in van der Waals heterostructures. Schuler, S. Controlled generation of a p—n junction in a waveguide integrated graphene photodetector. Konstantatos, G. Hybrid graphene—quantum dot phototransistors with ultrahigh gain. Kufer, D. Huo, N. Goosens, S. Broadband image sensor array based on graphene—CMOS integration.
Made of semi-conductor material and containing a p-n junction, it is designed to function in reverse bias. Current is produced in the photodiode when photons are absorbed and a small amount of current is also produced when there is no light present.go
Emerging technologies for high performance infrared detectors : Nanophotonics
With increase of the surface area, photodiodes have slower response times. Photodiode technology has been successfully and widely used due to its simple and low-cost rugged structure. Photodiodes have two different operation modes, namely photovoltaic mode and photoconductive mode.
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In photovoltaic mode, dependence on light is non-linear and the dynamic range achieved is fairly small. Maximum speed is also not obtained in photovoltaic mode. In photoconductive mode, the dependence on the light is very linear.
Reverse voltage has no significant influence on light, but has a weak influence on dark current current achieved without light. Photodiodes are widely used in the electronics industry, especially in detectors and wide bandwidth optical telecommunications systems. Toggle navigation Menu.
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