Exponential-gain values well in excess of 1,000 have been obtained in HgCdTe high-density, vertically integrated photodiode (HDVIP) avalanche photodiodes (APDs) with essentially zero excess noise. This phenomenon has been observed at temperatures in the range of 77-260 K for a variety of cutoff wavelengths in the mid-wavelength infrared (MWIR) band, with evidence of similar behavior in other IR bands. A theory for electron avalanche multiplication has been developed using density of states and electron-interaction matrix elements associated with the unique band structure of HgCdTe, with allowances being made for the relevant scattering mechanisms of both electrons and holes at these temperatures. This theory is used to develop an empirical model to fit the experimental data obtained at DRS Infrared Technologies. The functional dependence of gain on applied bias voltage is obtained by the use of one adjustable parameter relating electron energy to applied voltage. A more quantitative physical theory requires the use of Monte Carlo techniques incorporating the preceding scattering rates and ionization probabilities. This has been performed at the University of Texas at Austin, and preliminary data indicate good agreement with DRS models for both avalanche gain and excess noise as a function of applied bias. These data are discussed with a view to applications at a variety of wavelengths.

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.

This paper reports results obtained on mid-wave infrared (MWIR) x=O.3 Hg1CdTe avalanche photodiodes (APDs) that utilize a cylindrical "p-around-n" front side illuminated n+In-/p geometry. This "p-around-n" geometry favors electron avalanche gain. These devices are characterized by a uniform, exponential, gain voltage characteristic that is consistent with a hole to electron ionization ratio, k=ahlcte, of zero. At 6 V bias and 77 K, gains are typically near 50, and gains of over 100 have been measured at higher biases. Response times have been modeled and measured on these devices. The modeling indicates that the geometry and dimensions of the diode control the diffusion limited device bandwidth. Rise times of less than 0.35 nsec (1GHz bandwidth) should be possible according to this analysis. To date 10% to 90% rise times as low as 1 nsec have been measured. The gain is approximately noiseless up to gains of over fifty which is consistent with insignificant hole ionization (k=0). The noiseless gain behavior reported here is inconsistent with the original theory of McIntyre that predicts an excess noise factor of 2 for the k=0 case. The explanation for these results will require application of the modified "history dependent" theory for excess noise later proposed by McIntyre.

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

No abstract