A Theoretical Model for the HgCdTe Electron Avalanche Photodiode |
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Authors: | Michael A Kinch |
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Affiliation: | (1) DRS Infrared Technologies, Dallas, TX 75243, USA |
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Abstract: | A ballistic model is presented for electron avalanche multiplication in the conduction band of HgCdTe, based upon the concept
of an optical phonon limited mean free path for the electron, λ
e. The model predicts avalanche gain as a function of applied bias voltage V, and a threshold voltage for impact ionization V
th. Impact ionization probabilities are calculated analytically using a simplified band structure model for HgCdTe and used
to estimate values for the threshold energy for impact ionization. A simple ballistic model is developed to correlate the
relationship between electron energy and applied bias voltage, based upon the relevant electron scattering mechanisms in HgCdTe.
A comparison with published gain–voltage data suggests that the process is limited by optical phonon scattering, and the relationship
between electron energy and applied bias voltage, for a uniform electric field F = V/W, across a diode depletion width W, is given by E = α(E)V, where α(E) = λ
e(E)/W]. For high electron energies λ
e(E) is independent of E and α(E) depends only on the dielectric parameters of the material. Using this simple model it is easy to predict electron avalanche
gain versus voltage for any parametric combination of diode geometry, bandgap, and operating temperature. |
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Keywords: | HgCdTe electron avalanche photodiode optical phonon mean free path impact ionization |
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