History-Dependent Impact Ionization Theory Applied
to HgCdTe e-APDs |
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Authors: | Johan Rothman Laurent Mollard Sylvain Goût Leo Bonnefond Jerôme Wlassow |
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Affiliation: | (1) CEA/LETI/DOPT 17, rue des Martyrs, 38054 Grenoble Cedex 9, France; |
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Abstract: | The variation of the gain and the excess noise factor in HgCdTe avalanche photodiodes (APDs) with different junction geometries
are compared with published theoretical and numerical work. It is shown that, although some features of the gain curves are
reproduced, such as the constant exponential increase in the gain, the theoretical work fails to predict the observed variation
of the gain as a function of multiplication layer width. In contrast, a new analytical gain model based on local impact ionization
coefficients and a first direct comparison of the prediction of history-dependent impact ionization theory are shown to give
a good general fit to the experimental gain data. A generic model of the gain in HgCdTe APDs has been obtained by fitting
the analytical local model to gain curves of APDs with various geometries and cut-off wavelengths. The study of different
hypotheses on the electric field dependence of the dead-space length and the saturation value of the impact ionization coefficient
has shown that a variable dead-space effect has a direct impact on the excess noise of APDs, which is why exact excess noise
measurements are necessary to achieve a pertinent estimation of the nonlocal impact ionization function. |
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