Ionization energies in Cd_xHg_1-xTe avalanche photodiodes

Abstract

The Cd,Hg, -;re avalanche photodiodes present hole or electron majority mu!!iplicationi depending on the r valuesl with a ratio of infiizattion fa.ctQrs k = ?,I%, maximum for x = 0.6 and minimum for x = 0.4. This behaviour is explained by a simulation of the multiplication phenomenon. Monte Carlo electron traiectories are averaged to obtain ionization factors ah and G. This model introduces a linear relationship between the logarithm of k and the ionization energy difference for holes and electrons: AE, = E,, -E,-. We compute this energy difference in an empirical tight binding band structure and show that its variation versus x agrees with experimental k(x) variations. The hole multiplication maximum at x = 0.6 is explained as the effect of transitions issued from the

HgCdTe MWIR Back-Illuminated Electron-Initiated Avalanche Photodiode Arrays

“…The advantages of the HgCdTe energy band structure for APDs were elucidated through the theoretical analyses of Leveque et al 1 They describe two regimes in which the ratio k = a h /a e of the hole ionization coefficient a h to the electron ionization coefficient a e is either much greater or much less than unity. For cutoff wavelengths shorter than approximately 1.9 lm (x = 0.56 at 300 K), they predict a h >> a e because of resonant enhancement of the hole ionization coefficient when the energy bandgap is near or equal to the spin-orbit splitting energy 2 D 0 ( = 0.938 eV).…”

Infrared Avalanche Photodiode Detectors

“…Asymmetry between effective mass of electron in the conduction band and heavy hole results in the unequal ionisation coefficient for electron and hole in HgCdTe material [25][26][27][28] . Electron mobility is two orders of magnitude higher than holes in HgCdTe due to their different scattering rates in HgCdTe.…”

“…High avalanche gain with low noise is obtained as impact ionisation process is initiated by one type of carriers, electron injection for lower x-values (x < 0.6) or hole injection for 25 0.6 < x < 0.7. The composition dependence of ionisation coefficient ratio in Hg 1-x Cd x Te is described as (a) when Δ > E g , composition x < 0.6, and 0 ≤ k < 1; electron is dominant in the multiplication process (Δ=spin-orbit splitting energy), (b) when Δ < E g , composition x > 0.7 and k >> 1; hole is dominant in the multiplication process, (c) when Δ ≈ E g (at resonance), composition 0.6 < x < 0.7 and k~1; hole is dominant in the multiplication process 25,28 . The excess noise and bandwidth (BW) of APD are determined by α e and α h in the multiplication region, which are the characteristics of the material 2 .…”

Experimental Performance and Monte Carlo Modeling of Long Wavelength Infrared Mercury Cadmium Telluride Avalanche Photodiodes

“…A quasi-single impact ionization process in Hg 1Àx Cd x Te is possible with electrons (very low hole to electron impact ionization coefficient ratio k < 0.1 for x < 0.53, corresponding to a cut-off wavelength k c ‡ 2 lm) as well as with holes (high k % 30 around x = 0.6-0.7, corresponding to 1.5 lm < k c < 1.8 lm). 1 Hence, Hg 1Àx Cd x Te electron-injected avalanche photodiodes are exceptional amplifiers for incoming photon flux in short-wavelength infrared (SWIR), MWIR and LWIR 2-10 for cut-off wavelengths from 2.2 lm to 11 lm (x from 0.7 to 0.2). The overall sensitivity of such detectors is enhanced by reduction of the contribution of the noise introduced by readout integrated circuits and front-end amplifiers.…”