Electron injection avalanche photodiodes in short-wave infrared (SWIR) to long-wave infrared (LWIR) HgCdTe show gain and excess noise properties indicative of a single ionizing carrier gain process. The result is an electron avalanche photodiode (EAPD) with ''ideal'' APD characteristics including near noiseless gain. This paper reports results obtained on long-, mid-, and shortwave cutoff infrared Hg 1ÿ x Cd x Te EAPDs (10 mm, 5 mm, and 2.2 mm) that use a cylindrical ''p-around-n'' front side illuminated n1/n-/p geometry that favors electron injection into the gain region. These devices are characterized by a uniform, exponential, gain voltage characteristic that is consistent with a hole-to-electron ionization coefficient ratio, k 5 a h /a e , of zero. Gains of greater than 1,000 have been measured in MWIR EAPDS without any sign of avalanche breakdown. Excess noise measurements on midwave infrared (MWIR) and SWIR EAPDs show a gain independent excess noise factor at high gains that has a limiting value less than 2. At 77 K, 4.3-mm cutoff devices show excess noise factors of close to unity out to gains of 1,000. A noise equivalent input of 7.5 photons at a 10-ns pulsed signal gain of 964 measured on an MWIR APD at 77 K provides an indication of the capability of this new device. The excess noise factor at room temperature on SWIR EAPDs, while still consistent with the k 5 0 operation, approaches a gain independent limiting value of just under 2 because of electron-phonon interactions expected at room temperature. The k 5 0 operation is explained by the band structure of the HgCdTe. Monte Carlo modeling based on the band structure and scattering models for HgCdTe predict the measured gain and excess noise behavior.
An overview of recent improvements in our understanding of, and the maturity of, linear-mode photon counting with the HgCdTe electron-initiated avalanche photodiode is presented. In 2010 DRS fabricated an experimental 2 9 8 array with (64 lm) 2 pixels which enabled, for the first time, linear-mode photon counting by use of the MWIR cutoff HgCdTe electron-initiated avalanche photodiode. The device had a high single-photon signal-to-noise ratio of 13.7, an excess noise factor of 1.3-1.4, a 7 ns minimum time between events, and a broad spectral response extending from 0.4 lm to 4.2 lm. DRS recently fabricated a new set of devices with improved yield and performance compared with the first device: the false event rate was reduced by a factor of almost 10 to 150 kHz, the photon detection efficiency was increased from 50% to >60%, and the APD gain was increased by a factor of 4 to over 1900.
Electron injection avalanche photodiodes in SWIR to LWIR HgCdTe show gain and excess noise properties indicative of a single ionizing carrier gain process. The result is an electron avalanche photodiode (EAPD) with "ideal" APD characteristics including near noiseless gain. This paper reports results obtained on mid-wave, short-wave, and long-wave cutoff infrared
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