InAs avalanche photodiodes (APDs) can be designed such that only electrons are allowed to initiate impact ionization, leading to the lowest possible excess noise factor. Optimization of wet chemical etching and surface passivation produced mesa APDs with bulk dominated dark current and responsivity that are comparable and higher, respectively, than a commercial InAs detector. Our InAs electron-APDs also show high stability with fluctuation of ~0.1% when operated at a gain of 11.2 over 60 s. These InAs APDs can detect very weak signal down to ~35 photons per pulse. Fabrication of planar InAs by Be implantation produced planar APDs with bulk dominated dark current. Annealing at 550 °C was necessary to remove implantation damage and to activate Be dopants. Due to minimal diffusion of Be, thick depletion of 8 μm was achieved. Since the avalanche gain increases exponentially with the thickness of avalanche region, our planar APD achieved high gain > 300 at 200 K. Our work suggest that both mesa and planar InAs APDs can exhibit high gain. When combined with a suitable preamplifier, single photon detection using InAs electron-APDs could be achieved.
Sensitive detection of mid-infrared light (2 to 5 μm wavelengths) is crucial to a wide range of applications. Many of the applications require high-sensitivity photodiodes, or even avalanche photodiodes (APDs), with the latter generally accepted as more desirable to provide higher sensitivity when the optical signal is very weak. Using the semiconductor InAs, whose bandgap is 0.35 eV at room temperature (corresponding to a cut-off wavelength of 3.5 μm), Sheffield has developed high-sensitivity APDs for mid-infrared detection for one such application, satellite-based greenhouse gases monitoring at 2.0 μm wavelength. With responsivity of 1.36 A/W at unity gain at 2.0 μm wavelength (84 % quantum efficiency), increasing to 13.6 A/W (avalanche gain of 10) at -10V, our InAs APDs meet most of the key requirements from the greenhouse gas monitoring application, when cooled to 180 K. In the past few years, efforts were also made to develop planar InAs APDs, which are expected to offer greater robustness and manufacturability than mesa APDs previously employed. Planar InAs photodiodes are reported with reasonable responsivity (0.45 A/W for 1550 nm wavelength) and planar InAs APDs exhibited avalanche gain as high as 330 at 200 K. These developments indicate that InAs photodiodes and APDs are maturing, gradually realising their potential indicated by early demonstrations which were first reported nearly a decade ago.
KEYWORDS: Indium arsenide, Photodiodes, Sensors, Black bodies, Temperature metrology, Radiation thermometry, Signal to noise ratio, Diodes, Photodetectors, Optical amplifiers
We report on the evaluation of InAs photodiodes and their potential for low temperature sensing. InAs n-i-p photodiodes were grown and analyzed in this work. Radiation thermometry measurements were performed at reference blackbody temperatures of 37 to 80°C to determine photocurrent and temperature error. The uncooled InAs photodiodes, with a cutoff wavelength of 3.55 μm, detect a target temperature above 37°C with a temperature error of less than 0.46°C. When the photodiode was cooled to 200 K, the temperature error at 37°C improves by 10 times from 0.46 to 0.048°C, suggesting the potential of using InAs for human temperature sensing.
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