Recently, subwavelength plasmonic nanostructure gratings have been identified as promising candidates for realising high-speed improved-responsivity metal-semiconductor-metal photodetectors (MSM-PDs).
A subwavelength plasmonic nanostructure grating interacts strongly with the incident light and potentially traps it inside the subsurface region of semiconductor substrates. MSM-PDs are very promising candidates for a wide range of applications, such as optical fibre communication, high-speed chip-to-chip interconnects, and high-speed sampling.
MSM-PDs have a much smaller capacitance per unit area due to their lateral geometry. They have response times in the range of a few tens of picoseconds, due to the nano-scale spacings between the electrode fingers. However, the downsizing of the electrode spacing leads to a decreased active area, resulting in a degraded responsivity.
Recently, the use of surface plasmon-assisted effects for the design of such photodetectors has led to the development of MSM-PDs having a high responsivity-bandwidth product, well beyond that of conventional PIN photodetectors, thus attracting a great deal of interest.
The use of surface plasmon polaritons (SPPs) for light absorption enhancement using subwavelength metal gratings promises an increased enhancement in light collection efficiency. In the past decade, there have been several experimental and theoretical research and development activities reported on extraordinary optical transmission through subwavelength metallic apertures as well as through periodic metal grating structures.
Simulation results based on finite-difference time-domain (FDTD) method have shown significant enhancement of light absorption through interaction with SPPs, and this has direct application to the design of MSM-PDs. An accurate modelling of MSM-PDs will open the way for the development of high responsivity-bandwidth-product photodetectors that are attractive for many practical applications.
At the Electron Science Research Institute, our researchers are using FDTD analysis to predict the performance of a novel MSM-PD structure employing a single metal layer deposited onto a GaAs substrate and a nano-engineered metal grating etched lithographically into the metal (Au) layer above an unperturbed part of the same metal layer.
Particularly, we are focusing on the grating groove-shape-dependent properties of these MSM-PD devices, in order to evaluate the effects of device manufacturing technology-related limitations on the performance of these nano-grating patterns.
Our modelling results have shown that the novel MSM-PD structures can attain a maximum light absorption near 850 nm which is almost 50 times better than that achieved with conventionally-designed MSM-PDs.
Our researchers have manufactured several test samples of nanograting-assisted MSM-PDs using the Institute’s FIB lithography and are currently characterising the typical nano-grating groove profiles obtained using AFM imaging.
Dr Narottam Das
Professor Kamal Alameh
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