In this work, we have proposed a model for the ultimate physical limit on the sensitivity of the heterojunction bipolar phototransistors (HPTs). Based on our modeling we have extracted the design criteria for the HPT for high sensitivity application. HPT with the submicron emitter and base area has the potential to be used for the low number photon resolving in near-infrared (NIR) wavelength. However, in practice, the quality of materials, processing, and the passivation plays an important role in the realization of the highly sensitive HPT. For short wave infrared (SWIR) HPTs based on lattice matched InGaAs to InP is studied. For these devices, conditions to reach to the highest possible sensitivity is examined. We have made an HPT based on InGaAs collector and base on the InP substrate. After developing proper processing combination of wet and dry etching and the surface passivation for the device we made an imager with 320x256 pixels based with a 30m pixel pitch. The imager shows the sensitivity less the 30 photons for each pixel with the frame rate more than 1K frames per second.
This article reports the progress on the development of a novel detector with the promise of addressing the needs of extreme AO (ExAO) in the near-IR band (NIR), 0.9-1.7 μm. The camera is based on the electron injection mechanism which resembles how the human eye processes light. The camera design allows high sensitivity operation at TEC reachable temperatures for ExAO at 1-4 kHz frame rates, and at the same time the concept produces sufficient gain to overcome the read noise of the device. Here we present the overall design, test results on Gen-1 (outdated but operable) camera, along with early results of our next generation of detectors.
Our recently published results show a much reduced dark current and enhanced speed from our second-generation electron-Injection detectors, due to the introduction of an isolation method. However, these results have been limited to single-element detectors. A natural next step is to incorporate these new devices into a focal plane array (FPA), since we have already achieved very attractive results from an FPA based on the first-generation devices. Despite the high-performance characteristics of second generation devices, isolation introduces new processing steps and a robust procedure is required for realization of focal plane arrays (FPA) with good uniformity and yield. Here we report our systematic evaluation of the processing steps, and in particular the effect of the processing temperature, on the device dark current and uniformity. Our goal is to produce ultra-low dark current FPA based on isolated electron-injection detectors, and to approach single-photon sensitivity.
An ultra-small telecentric lens with sub-millimeter thickness is proposed. This lens with 0.2 numerical aperture and high field of view is a good candidate to be used in multi-aperture super resolution imagers. Point spread function and the telecentricity of the lens is extracted numerically and measured experimentally. The ray-optics simulation results show nearly diffraction limited performance for the lens.
A thermal photovoltaic cell (TPV) is an optical heat engine that can extract energy from an emitter with elevated temperature. In theory, the efficiency of a TPV can reach to 80% by wavelength conversion, yet in practice, only 3.2% efficiency has been achieved. The main physical drawback is to maintain the device operation at very high temperature while managing total solar spectrum absorption and efficient coupling of the narrow-band thermal radiation into the photovoltaic cell. In this vein, utilizing of a nanophotonic structure to undergo the wavelength conversion of solar energy is inevitable. Furthermore, low cost, large area and high throughput realization of such a structure brings TPV beyond the research lab.
Simultaneous tailoring of UV/visible and mid-infrared spectrums requires sub-100-nm feature size, which is challenging with conventional photolithography if it is not impossible. We have developed a microsphere deep-UV lithography that can produce minimum feature size of ~ 50 nm at extremely low cost and high throughput. In this work, we demonstrate a metasurface platform fabricated with this lithography technique which has omni-polarization and -angle absorption in visible spectrum and efficient emission at mid-infrared as confirmed both by FDTD simulation and Fourier transform infrared spectroscopy (FTIR) measurement. The developed technique is promising technology to expedite TPV in real-life energy harvesting applications.
We have introduce optomechanical nanoantennae, which showed dramatic changes in scattering
properties by minuscule changes in geometry. These structures are very compact, with a volume 500
times smaller than free space optical wavelength volume. Through these optical elements, far-field can
directly control the near-field of antenna by mechanical reconfiguration. Here we present the functionality
of the optomechanical nanoantenna and challenges in fabricating and measuring these devices.
Nano-fabrication technologies are usually associated with complication, high cost, and limited area of coverage.
However, advances in optics and nanophotonics constantly demand novel fabrications for nano-manufacturing
systems with extraordinary optical, electrical, mechanical, or thermal responses. While, these properties are vital for
health, energy, and information technology applications, proposing new methods of fabricating nanostructures that
can be compatible with high throughput and large scale manufacturing is quite desirable. Here, we propose a deep
ultra-violet (DUV) photolithography technique that can produce a variety of periodic nanostructure clusters with
sub-100 nm feature sizes. The method is based on microsphere nanolithography, which focuses DUV field into a socalled
photonic nano-jet – a propagative intensive field underneath the sphere. The position of a photonic nano-jet
can be moved by changing the angle of exposure. The DUV microsphere nanolithography is inherently self-aligned,
mask-less and optics-less (the bulky optical element such as lens is not required), which makes this method
attractive for low-cost and high-throughput nano-manufacturing schemes, such as roll-to-roll production. Here, we
present fabricated arrays of nanoscale complex structures to demonstrate the capabilities of this nanolithography