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Resonant ionization of shallow donors in electric field

In short: It is well known that semiconductors are non-conductive at low temperatures because the electrons freeze in their lowest energy state at impurities. However, a sudden rise of the conductivity can anyway occur at high electric fields due to resonant ionization. We discuss this effect using a simplified model of the energy states of donor impurities, and our results are similar to the predictions of more advanced models and in very good agreement with our experiment.

We report on our experimental observations of the resonant ionization of a phosphorus donor in silicon in a homogeneous electric field. It is well known that at low temperatures the donor electrons freeze in their lowest energy state at the donor atoms, hence the semiconductor (silicon in our case) becomes non-conductive. The effect of resonant ionization is expressed in the sudden rise of the conductivity of the sample at low temperature when the electric field approaches the critical value of ∼3.2 MVm−1 . This effect is discussed in our work in terms of field-induced interaction of the donor states using a simplified model based on the effective-mass theory. The model predicts that the binding of the electrons to the donors at low temperature weakens strongly in the vicinity of the critical field, the electrons are released from the donors and the material becomes conductive despite the low temperature. The results from our model are qualitatively similar to the previously published advanced model (based on the first-principles calculation), which predicts ionization thresholds at approximate fields of 2.45 and 3.25 MVm−1, the latter being in very good agreement with our experiment.

Details of the research are described in Physica Scripta 89, 085802 (2014)
doi:10.1088/0031-8949/89/8/085802

Authors

Ivan Ivanov and Erik Janzén

Contact

Ivan Ivanov, associate professor
Phone: +46 (0)13 28 25 32
E-mail: iiv@ifm.liu.se

 


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Last updated: 09/05/14