In-situ Proton Radiation Testing of 2.4 Micron Wavelength Extended InGaAs Photodiodes at Dry Ice and Room Temperatures (2021)


Abhay M. Joshi *1 , Shubhashish Datta 1 , Jeff Mertz 1 , Nilesh Soni 1 , Michael Sivertz 2 , Adam Rusek 2 , C. Pearson 2 , James Jardine 3
1 Discovery Semiconductors Inc., Ewing, NJ, USA
2 NASA Space Radiation Laboratory, Brookhaven National Laboratory, Upton, NY, USA.
3 Brookhaven National Laboratory, Upton, NY, USA.


We have successfully tested 290 µm diameter, 2.4 micron wavelength, Extended InGaAs photodiodes coupled with single mode fiber using 50 MeV Protons at both dry ice temperature (-75 °C) and room temperature (20 °C). The devices were reverse biased at 100 mV during the radiation run and their leakage current was continuously monitored insitu during the exposure. These devices find multiple applications in space for spectroscopy & sensing, inter-satellite optical communication links, rapid Doppler shift LIDAR, as well as inter-planetary and Earth-to-Moon communication links.

Several photodiodes were tested using 50 MeV Protons with an average flux level of 2.11 × 107 protons/cm2/s, for a total fluence of 1.0 × 1011 protons/cm2 and total dose of 20 krad (water). Pre- and post-radiation results were also measured for leakage current vs. voltage, responsivity (quantum efficiency), and bandwidth of the Extended InGaAs photodiodes. All devices were found to be fully functional at normal operating conditions and at both dry ice and room temperature.


Space-based spectroscopic missions, such as NASA’s upcoming Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) mission, require short-wave infrared (SWIR) photodiodes covering spectrum ranging from 900 nm to 2300 nm [1]. These instruments are based on direct detection sensors that operate at very low light levels from back-scattered sunlight. This leads to several competing requirements, especially for the longer wavelength spectral bands. It is desirable to increase the detector’s active area to improve its optical collection efficiency, while minimizing its leakage current to improve the signal-to-noise ratio (SNR). The photodiode’s leakage current may be reduced by operating it at low reverse bias; however, this may increase its capacitance and elevate the kTC noise in the post-detection read-out circuit to unacceptably high levels. The leakage current may be reduced by cooling the sensors, which in turn, increases the detector’s bandgap and reduces its cut-off wavelength. This additional design challenge requires the SWIR detectors to have smaller bandgap than would be required for higher temperature applications operating at, say 300 K. Smaller bandgap photodiodes not only have a propensity to have a high generation-recombination leakage current, but may be more susceptible to radiation damage in space.

Dual-Depletion Region (DDR) InP / InGaAs photodiode structure lends itself to lower leakage current, low capacitance, and increased resilience to radiation. Our prior work on Standard InGaAs and 2.2 micron wavelength Extended InGaAs DDR photodiodes has addressed a number of challenging space applications for wavelengths ranging from 800 nm to 2200 nm [2 - 6]. Here, we present a 290 µm Extended InGaAs DDR photodiode having a cut-off wavelength of 2400 nm at 300 K, and >80% quantum efficiency measured at 2050 nm wavelength. These photodiodes demonstrate nanoampere level dark current at 100 mV reverse bias when cooled below -50 °C, which is more than adequate to meet the SNR specifications for space-based spectroscopy, e.g. NASA’s PACE mission. Such moderate cooling blue-shifts the cut-off wavelength by ~80 nm and assures high quantum efficiency up to 2300 nm wavelength. Owing to the low-capacitance DDR photodiode structure, the device capacitance is less than 20 pF at 100 mV reverse bias for 290 µm diameter photodiode. All these features make these Extended InGaAs DDR photodiodes a prime candidate for inclusion in spectroscopic space missions.

Space qualification of these devices will not only enable spectroscopic missions, but also have an impact on other space applications, such as LIDAR and optical communication links, which operate at higher temperatures and higher optical power levels. Therefore, we proceeded to comprehensively test these devices for harsh space environment by subjecting them to 50 MeV Protons, Gamma rays, 1 GeV/n Alpha particles (He ions), and 1 GeV/n Fe ions. These tests were successful and performed on multiple devices biased at 100 mV at ambient room temperature as well as -75 °C temperature using dry ice. The dark current was monitored in-situ during radiation to corroborate extensive pre- and post-radiation measurements and to rule out any potential room temperature annealing effects. The scope of this paper is limited to narrating the successful 50 MeV Proton radiation tests up to a fluence of 1.0 × 1011 protons/cm2. The Gamma, Alpha particle, and heavy ion radiation test results will be presented elsewhere.


Event: SPIE Defense + Commercial Sensing, 2021, Online Only


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